ICE CREAM MANUFACTURE

Friandise

ingredients makes about 48 oil for greasing 8 cherries 8 grapes 8 small strawberries 8 cherries 1 satsuma, in segments 8 Brazil nuts 7/8 cup (200 g) 7 oz granulated sugar method 1. Prepare the fruit, leaving the stems on the cherries, grapes, strawberries and cherries. 2. Remove any pith from the satsuma segments. 3. Generously grease a large baking sheet and have ready 2 oiled forks. 4. Put the sugar in a heavy bottomed saucepan and add 175 ml (6 fl oz) water. 5. Heat gently, stirring until the sugar has dissolved. Increase the heat and boil the syrup until it turns a pale gold in colour. 6. Immediately remove the pan from the heat and dip the bottom of the pan in cold water to prevent the syrup from darkening any further. 7. Spear a fruit or nut on a fork, dip it in the hot caramel syrup, then allow the excess caramel to drip back into the pan. 8. Use the second fork to ease the fruit or nut on to the baking sheet. 9. Continue until all the fruits and nuts have been glazed, warming the syrup gently if it becomes too thick to use. 10. When the coating on all the fruits and nuts has hardened, lift them carefully off the baking sheet. 11. Serve in paper sweet cases.

Orange friandises 

Ingredients

• 125gground almonds
• 60gcake flour, sifted
• 70gicing sugar, sifted
• 6egg whites
• 180gbutter, melted
• 15mlgrated orange peel
• icing sugar for dusting

Method

Combine almonds, flour and icing sugar in a mixing bowl, whisk egg whites in a separate bowl, preferably with a balloon whisk, until soft peaks form. Fold into flour mixture with melted butter. Stir in grated orange peel and mix well. Spoon mixture into greased tartlet pans. Bake at 200 ºC for 15 to 20 minutes. Dust with icing sugar and serve warm or cool, with coffee or tea.

Ice Cream Manufacture

The basic steps in the manufacturing of ice cream are generally as follows:

• blending of the mix ingredients
• pasteurization
• homogenization
• aging the mix
• freezing
• packaging
• hardening

Process flow diagram for ice cream manufacture: the red section represents the operations involving raw, unpasteurized mix, the pale blue section represents the operations involving pasteurized mix, and the dark blue section represents the operations involving frozen ice cream.

Blending

First the ingredients are selected based on the desired formulation and the calculation of the recipe from the formulation and the ingredients chosen, then the ingredients are weighed and blended together to produce what is known as the "ice cream mix". Blending requires rapid agitation to incorporate powders, and often high speed blenders are used.

Pasteurization

The mix is then pasteurized. Pasteurization is the biological control point in the system, designed for the destruction of pathogenic bacteria. In addition to this very important function, pasteurization also reduces the number of spoilage organisms such as psychrotrophs, and helps to hydrate some of the components (proteins, stabilizers).

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Pasteurization (Ontario regulations): 69° C/30 min. 80° C/25s

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Both batch pasteurizers and continuous (HTST) methods are used.
Batch pasteurizers lead to more whey protein denaturation, which some people feel gives a better body to the ice cream. In a batch pasteurization system, blending of the proper ingredient amounts is done in large jacketed vats equipped with some means of heating, usually steam or hot water. The product is then heated in the vat to at least 69 C (155 F) and held for 30 minutes to satisfy legal requirements for pasteurization, necessary for the destruction of pathogenic bacteria. Various time temperature combinations can be used. The heat treatment must be severe enough to ensure destruction of pathogens and to reduce the bacterial count to a maximum of 100,000 per gram. Following pasteurization, the mix is homogenized by means of high pressures and then is passed across some type of heat exchanger (plate or double or triple tube) for the purpose of cooling the mix to refrigerated temperatures (4 C). Batch tanks are usually operated in tandem so that one is holding while the other is being prepared. Automatic timers and valves ensure the proper holding time has been met.
Continuous pasteurization (see schematic diagram for mix here) is usually performed in a high temperature short time (HTST) heat exchanger following blending of ingredients in a large, insulated feed tank. Some preheating, to 30 to 40 C, is necessary for solubilization of the components. The HTST system is equipped with a heating section, a cooling section, and a regeneration section. Cooling sections of ice cream mix HTST presses are usually larger than milk HTST presses. Due to the preheating of the mix, regeneration is lost and mix entering the cooling section is still quite warm.

Homogenization

The mix is also homogenized which forms the fat emulsion by breaking down or reducing the size of the fat globules found in milk or cream to less than 1 µ m. Two stage homogenization is usually preferred for ice cream mix. Clumping or clustering of the fat is reduced thereby producing a thinner, more rapidly whipped mix. Melt-down is also improved. Homogenization provides the following functions in ice cream manufacture:

• Reduces size of fat globules
• Increases surface area
• Forms membrane
• makes possible the use of butter, frozen cream, etc.

By helping to form the fat structure, it also has the following indirect effects:

• makes a smoother ice cream
• gives a greater apparent richness and palatability
• better air stability
• increases resistance to melting

Homogenization of the mix should take place at the pasteurizing temperature. The high temperature produces more efficient breaking up of the fat globules at any given pressure and also reduces fat clumping and the tendency to thick, heavy bodied mixes. No one pressure can be recommended that will give satisfactory results under all conditions. The higher the fat and total solids in the mix, the lower the pressure should be. If a two stage homogenizer is used, a pressure of 2000 - 2500 psi on the first stage and 500 - 1000 psi on the second stage should be satisfactory under most conditions. Two stage homogenization is usually preferred for ice cream mix. Clumping or clustering of the fat is reduced thereby producing a thinner, more rapidly whipped mix. Melt-down is also improved.

Ageing

The mix is then aged for at least four hours and usually overnight. This allows time for the fat to cool down and crystallize, and for the proteins and polysaccharides to fully hydrate. Aging provides the following functions:

• Improves whipping qualities of mix and body and texture of ice cream

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It does so by:

• providing time for fat crystallization, so the fat can partially coalesce;
• allowing time for full protein and stabilizer hydration and a resulting slight viscosity increase;
• allowing time for membrane rearrangement and protein/emulsifier interaction, as emulsifiers displace proteins from the fat globule surface, which allows for a reduction in stabilization of the fat globules and enhanced partial coalescence.

Aging is performed in insulated or refrigerated storage tanks, silos, etc. Mix temperature should be maintained as low as possible without freezing, at or below 5 C. An aging time of overnight is likely to give best results under average plant conditions. A "green" or unaged mix is usually quickly detected at the freezer.

Freezing and Hardening

Following mix processing, the mix is drawn into a flavour tank where any liquid flavours, fruit purees, or colours are added. The mix then enters the dynamic freezing process which both freezes a portion of the water and whips air into the frozen mix. The "barrel" freezer is a scraped-surface, tubular heat exchanger, which is jacketed with a boiling refrigerant such as ammonia or freon. Mix is pumped through this freezer and is drawn off the other end in a matter of 30 seconds, (or 10 to 15 minutes in the case of batch freezers) with about 50% of its water frozen. There are rotating blades inside the barrel that keep the ice scraped off the surface of the freezer and also dashers inside the machine which help to whip the mix and incorporate air.

Ice cream contains a considerable quantity of air, up to half of its volume. This gives the product its characteristic lightness. Without air, ice cream would be similar to a frozen ice cube. The air content is termed its overrun, which can be calculated mathematically.
As the ice cream is drawn with about half of its water frozen, particulate matter such as fruits, nuts, candy, cookies, or whatever you like, is added to the semi-frozen slurry which has a consistency similar to soft-serve ice cream. In fact, almost the only thing which differentiates hard frozen ice cream from soft-serve, is the fact that soft serve is drawn into cones at this point in the process rather than into packages for subsequent hardening.

Hardening

After the particulates have been added, the ice cream is packaged and is placed into a blast freezer at -30° to -40° C where most of the remainder of the water is frozen. Below about -25° C, ice cream is stable for indefinite periods without danger of ice crystal growth; however, above this temperature, ice crystal growth is possible and the rate of crystal growth is dependant upon the temperature of storage. This limits the shelf life of the ice cream.

A primer on the theoretical aspects of freezing will help you to fully understand the freezing and recrystallization process.
Hardening invloves static (still, quiescent) freezing of the packaged products in blast freezers. Freezing rate must still be rapid, so freezing techniques involve low temperature (-40oC) with either enhanced convection (freezing tunnels with forced air fans) or enhanced conduction (plate freezers).

The rate of heat transfer in a frezing porcess is affected by the temperature difference, the surface area exposed and the heat transfer coefficient (Q=U A dT). Thus, the factors affecting hardening are those affecting this rate of heat transfer:

• Temperature of blast freezer - the colder the temperature, the faster the hardening, the smoother the product.
• Rapid circulation of air - increases convective heat transfer.
• Temperature of ice cream when placed in the hardening freezer - the colder the ice cream at draw, the faster the hardening; - must get through packaging operations fast.
• Size of container - exposure of maximum surface area to cold air, especially important to consider shrink wrapped bundles - they become a much larger mass to freeze. Bundling should be done after hardening.
• Composition of ice cream - related to freezing point depression and the temperature required to ensure a significantly high ice phase volume.
• Method of stacking containers or bundles to allow air circulation. Circulation should not be impeded - there should be no 'dead air' spaces (e.g., round vs. square packages).
• Care of evaporator - freedom from frost - acts as insulator.
• Package type, should not impede heat transfer - e.g., styrofoam liner or corrugated cardboard may protect against heat shock after hardening, but reduces heat transfer during freezing so not feasible.

Ice cream from the dynamic freezing process (continuous freezer) can also be transformed into an array of novely/impulse products through a variety of filling and forming machines, which have ben identified on a separate page.

Ice Cream Ingredients

Ice cream has the following composition:

• greater than 10% milkfat by legal definition, and usually between 10% and as high as 16% fat in some premium ice creams
• 9 to 12% milk solids-not-fat: this component, also known as the serum solids, contains the proteins (caseins and whey proteins) and carbohydrates (lactose) found in milk
• 12 to 16% sweeteners: usually a combination of sucrose and glucose-based corn syrup sweeteners
• 0.2 to 0.5% stabilizers and emulsifiers
• 55% to 64% water which comes from the milk or other ingredients

These percentages are by weight, either in the mix or in the frozen ice cream. Please remember, however, that when frozen, about one half of the volume of ice cream is air (overrun, for definition, see ice cream processing, for calculation, see overrun), so by volume in ice cream, these numbers can be reduced by approximately one-half, depending on the actual air content. However, since air does not contribute weight, we usually talk about the composition of ice cream on a weight basis, bearing in mind this important distinction. All ice cream flavours, with the possible exception of chocolate, are made from a basic white mix.
Formulations can be derived from a number of different starting points. Details and suggested formulas are detailed on the formulations page, but turning the formulation into a recipe depends on the ingredients used to supply the components, and it is then necessary to do a mix calculation to determine the required ingredients based on the formula. Ice milk and light ice creams are very similar to the composition of ice cream but in the case of ice milk in Canada, for example, it must contain between 3% and 5% milkfat by legal definition.
The ingredients to supply the desired components are chosen on the basis of availability, cost, and desired quality. These ingredients will now be examined in more detail.

Milkfat (or "Butterfat") / Fat

Milkfat, or fat in general, including that from non0dairy sources, is important to ice cream for the following reasons:

• increases the richness of flavour in ice cream
• produces a characteristic smooth texture by lubricating the palate
• helps to give body to the ice cream, due to its role in fat destabilization
• aids in good melting properties, also due to its role in fat destabilization
• aids in lubricating the freezer barrel during manufacturing (Non-fat mixes are extremely hard on the freezing equipment)

The limitations of excessive use of butterfat in a mix include:

• cost
• hindered whipping ability
• decreased consumption due to excessive richness
• high caloric value

The best source of butterfat in ice cream for high quality flavour and convenience is fresh sweet cream from fresh sweet milk. Other sources include butter or anhydrous milkfat.

During freezing of ice cream, the fat emulsion which exists in the mix will partially destabilize or churn as a result of the air incorporation, ice crystallization and high shear forces of the blades. This partial churning is necessary to set up the structure and texture in ice cream, which is very similar to the structure in whipped cream. Emulsifiers help to promote this destabilization process, which will be discussed below.
The triglycerides in milkfat have a wide melting range, +40° C to -40° C, and thus there is always a combination of liquid and crystalline fat. Alteration of this solid: liquid ratio can affect the amount of fat destabilization that occurs. Duplicating this structure with other sources of fat is difficult.
Vegetable (non-dairy) fats are used extensively as fat sources in ice cream in the United Kingdom, parts of Europe, the Far East, and Latin America but only to a very limited extent in North America. Five factors of great interest in selection of fat source are the crystal structure of the fat, the rate at which the fat crystallizes during dynamic temperature conditions, the temperature-dependent melting profile of the fat, especially at chilled and freezer temperatures, the content of high melting triglycerides (which can produce a waxy, greasy mouthfeel) and the flavor and purity of the oil. It is important that the fat droplet contain an intermediate ratio of liquid:solid fat at the time of freezing. It is difficult to quantify this ratio as it is dependent on a number of composition and manufacturing factors, however, 1/2 to 2/3 crystalline fat at 4-5oC is a good, working rule. Crystallization of fat occurs in three steps: undercooling to induce nucleation, heterogeneous or homogeneous nucleation (or both), and crystal propagation. In bulk fat, nucleation is predominantly heterogeneous, with crystals themselves acting as nucleating agents for further crystallization, and undercooling is usually minimal. However, in an emulsion, each droplet must crystallize independently of the next. For heterogeneous nucleation to predominate, there must be a nucleating agent available in every droplet, which is often not the case. Thus in emulsions, homogeneous nucleation and extensive undercooling may be common. Blends of oils are often used in ice cream manufacture, selected to take into account physical characteristics, flavor, availability, stability during storage and cost.
We have recently completed a study on the use of non-dairy fats in frozen desserts, which is available here. A blend of 75% of either fractionated palm kernel oil or coconut oil and 25% of an unsaturated oil, like high oleic sunflower oil, was shown to produce optimal levels of fat destabilization, meltdown and flavour, although coconut oil may take longer to crystallize during aging. Blends of 50% milkfat, 37.5% fractionated palm kernel or coconut oil, and 12.5% high oleic sunflower oil were also shown to be very acceptable.

Milk Solids-not-fat

The serum solids or milk solids-not-fat (MSNF) contain the lactose, caseins, whey proteins, minerals, and ash content of the product from which they were derived. They are an important ingredient for the following beneficialreasons:

• improve the texture of ice cream, due to the protein functionality
• help to give body and chew resistance to the finished product
• are capable of allowing a higher overrun without the characteristic snowy or flaky textures associated with high overrun, due also to the protein functionality
• may be a cheap source of total solids, especially whey powder

The limitations on their use include off flavours which may arise from some of the products, and an excess of lactose which can lead to the defect of sandiness prevelant when the lactose crystallizes out of solution. Excessive concentrations of lactose in the serum phase may also lower the freezing point of the finished product to an unacceptable level.

The best sources of serum solids for high quality products are:

• concentrated skimmed milk
• spray process low heat skimmilk powder

Other sources of serum solids include: sweetened condensed whole or skimmed milk, frozen condensed skimmed milk, buttermilk powder or condensed buttermilk, condensed whole milk, or dried or condensed whey. Superheated condensed skimmed milk, in which high viscosity is promoted, is sometimes used as a stabilizing agent but does, then, also contribute to serum solids.

It has recently become common practice to replace the use of skim milk powder or condensed skim with a variety of milk powder replacers, which are blends of whey protein concentrates, caseinates, and whey powders. These are formulated with less protein than skim powder, usually 20-25% protein, and thus less cost, but are blended with an appropriate balance of whey proteins and caseins to do an adequate job. Caution must be exercised in excessive use of these powders, experimentation with your own mix is the best answer.
See the section on Concentrated and Dried Dairy Products for a description of the manufacture of all of the above ingredients.
The proteins, which make up approximately 4% of the mix, contribute much to the development of structure in ice cream including:

• emulsification properties in the mix
• whipping properties in the ice cream
• water holding capacity leading to enhanced viscosity and reduced iciness

Lactose Crystallization

1. A decrease in temperature favours rapid crystallization insofar as it increases the supersaturation.
2. A decrease in temperature favours slow crystallization insofar as it increases the viscosity, reduces the kinetic energy of the particles, and decreases the rate of transformation from beta to alpha lactose.

Supersaturated state can exist, however, due to extreme viscosity, and it is likely that much of the lactose in ice cream is non-crystalline. Stabilizers help to hold lactose in supersaturated state due to viscosity enhancement. Fruits, nuts, candy - add crystal centers and may enhance lactose crystallization. Nuts pull out moisture from ice cream immediately surrounding the nut thus concentrating the mix.

Citrate and phosphate ions decrease tendency for fat coalescence (Sodium citrate, Disodium Phosphate). They prevent churning in soft ice cream for example, producing a wetter product. These salts decrease the degree of protein aggregation. Calcium and magnesium ions have the opposite effect, promote partial coalescence. Calcium sulfate, for example, results in a drier ice cream. Calcium and Magnesium increase the degree of protein aggregation.
Salts may also influence electrostatic interactions. Fat globules carry a small net negative charge, these ions could increase or decrease that charge as they were attracted to or repelled from surface.

Sweeteners

A sweet ice cream is usually desired by the consumer. As a result, sweetening agents are added to ice cream mix at a rate of usually 12 - 16% by weight. Sweeteners improve the texture and palatability of the ice cream, enhance flavors, and are usually the cheapest source of total solids.

In addition, the sugars, including the lactose from the milk components, contribute to a depressed freezing point so that the ice cream has some unfrozen water associated with it at very low temperatures typical of their serving temperatures, -15° to -18° C. Without this unfrozen water, the ice cream would be too hard to scoop. See also the discussion of freeze concentration in the ice cream structure section. The effect of sweeteners on freezing characteristics of ice cream mixes is demonstrated by the plot shown on the ice cream freezing curve.
Sucrose is the main sweetener used because it imparts excellent flavour. Sucrose is a disaccharide made up of glucose (dextrose, cerelose), and fructose (levulose). Sucrose is dextrorotatory - meaning it rotates a plane of polarized light to the right, + 66.5° . With hydrolyzed sucrose the plane of polarization is to the left, "inverted" -20° . An acid, plus water, plus heat treatment, at concentrations above 10%, yields invert sugar and increases the sweetness.
It has become common in the industry to substitute all or a portion of the sucrose content with sweeteners derived from corn syrup. This sweetener is reported to contribute a firmer and more chewy body to the ice cream, is an economical source of solids, and improves the shelf life of the finished product. Corn syrup in either its liquid or dry form is available in varying dextrose equivalents (DE). The DE is a measure of the reducing sugar content of the syrup calculated as dextrose and expressed as a percentage of the total dry weight. As the DE is increased by hydrolysis of the corn starch, the sweetness of the solids is increased and the average molecular weight is decreased. This results in an increase in the freezing point depression, in such foods as ice cream, by the sweetener. The lower DE corn syrup contains more dextrins which tie up more water in the mix thus supplying greater stabilizing effect against coarse texture.
An enzymatic hydrolysis and isomerization procedure can convert glucose to fructose, a sweeter carbohydrate, in corn syrups thus producing a blend (high fructose corn syrup, HFCS) which can be used to a much greater extent in sucrose replacement. However, these HFCS blends further reduce the freezing point producing a very soft ice cream at usual conditions of storage and dipping in the home.
Here is a diagram illustrating the effect of DE and maltose or fructose conversion on the properties of corn starch hydrolysates as used in ice cream.
A balance is involved between sweetness, total solids, and freezing point.

Stabilizers

The stabilizers are a group of compounds, usually polysaccharide food gums, that are responsible for adding viscosity to the mix and the unfrozen phase of the ice cream. This results in many functional benefits, listed below, and also extends the shelf life by limiting ice recrystallization during storage. Without the stabilizers, the ice cream would become coarse and icy very quickly due to the migration of free water and the growth of existing ice crystals.

Effect of stabilizer on ice crystal size in ice cream 17 KB
The smaller the ice crystals in the ice cream, the less detectable they are to the tongue. Especially in the distribution channels of today's marketplace, the supermarkets, the trunks of cars, and so on, ice cream has many opportunities to warm up, partially melt some of the ice, and then refreeze as the temperature is once again lowered (see also the discussion on the fundamental aspects of freezing and ice cream shelf life for a more in-depth look at this process, and some discussion regarding the role of stabilizers in inhibiting it). This process is known as heat shock and every time it happens, the ice cream becomes more icy tasting. Stabilizers help to prevent this.
The functions of stabilizers in ice cream are:

• In the mix: To stabilize the emulsion to prevent creaming of fat and, in the case of carrageenan, to prevent serum separation due to incompatibility of the other polysaccharides with milk proteins, also to aid in suspension of liquid flavours
• In the ice cream at draw from the scraped surface freezer: To stabilize the air bubbles and to hold the flavourings, e.g., ripple sauces, in dispersion
• In the ice cream during storage: To prevent lactose crystal growth and retard or reduce ice crystal growth during storage (see also the discussion on ice cream shelf life, which discusses the mode of action of stabilizers in affecting ice recrystallization), also to prevent shrinkage from collapse of the air bubbles and to prevent moisture migration into the package (in the case of paperboard) and sublimation from the surface
• In the ice cream at the time of consumption: To provide some body and mouthfeel without being gummy, and to promote good flavour release
• (Note: all of the above, except perhaps for their role in retarding ice crystallization, can be attributable to the viscosity increase in the unfrozen phase of the ice cream)

Limitations on their use include:

• production of undesirable melting characteristics, due to too high viscosity
• excessive mix viscosity prior to freezing
• contribution to a heavy or chewy body

The stabilizers in use today include:

Locust Bean Gum:

soluble fibre of plant material derived from the endosperm of beans of exotic trees grown mostly in Africa (Note: locust bean gum is a synonym for carob bean gum, the beans of which were used centuries ago for weighing precious metals, a system still in use today, the word carob and Karat having similar derivation)

Guar Gum:

from the endosperm of the bean of the guar bush, a member of the legume family grown in India for centuries and now grown to a limited extent in Texas

Carboxymethyl cellulose (CMC):

derived from the bulky components, or pulp cellulose, of plant material, and chemically derivatized to make it water soluble

Xanthan gum:

produced in culture broth media by the microorganism Xanthaomonas campestris as an exopolysaccharide, used to a lesser extent

Sodium alginate:

an extract of seaweed, brown kelp, also used to a lesser extent

Carrageenan:

an extract of Irish Moss or other red algae, originally harvested from the coast of Ireland, near the village of Carragheen but now most frequently obtained from Chile and the Phillipines

Each of the stabilizers has its own characteristics and often, two or more of these stabilizers are used in combination to lend synergistic properties to each other and improve their overall effectiveness. Guar, for example, is more soluble than locust bean gum at cold temperatures, thus it finds more application in HTST pasteurization systems. Carrageenan is not used by itself but rather is used as a secondary colloid to prevent the wheying off of mix which is usually promoted by one of the other stabilizers.

Gelatin, a protein of animal origin, was used almost exclusively in the ice cream industry as a stabilizer but has gradually been replaced with polysaccharides of plant origin due to their increased effectiveness and reduced cost.

Emulsifiers

The emulsifiers are a group of compounds in ice cream that aid in developing the appropriate fat structure and air distribution necessary for the smooth eating and good meltdown characteristics desired in ice cream. Since each molecule of an emulsifier contains a hydrophilic portion and a hydrophobic portion, they reside at the interface between fat and water. As a result they act to reduce the interfacial tension or the force which exists between the two phases of the emulsion. This causes a desorption of protein from the fat droplet surface, which promotes a destabilization of the fat emulsion (due to a weaker membrane) leading to a smooth, dry product with good meltdown properties. Their action will be more fully explained in the structure of ice cream section.

The original ice cream emulsifier was egg yolk, which was used in most of the original recipes. Today, two emulsifiers predominate most ice cream formulations:

mono- and di-glycerides:

derived from the partial hydrolysis of fats or oils of animal or vegetable origin

polysorbate 80:

a sorbitan ester consisting of a glucose alcohol (sorbitol) molecule bound to a fatty acid, oleic acid, with oxyethylene groups added for further water solubility

Other possible sources of emulsifiers include buttermilk, and glycerol esters. All of these compounds are either fats or carbohydrates, important components in most of the foods we eat and need. Together, the stabilizers and emulsifiers make up less than one half percent by weight of our ice cream. They are all compounds which have been exhaustively tested for safety and have received the "generally recognized as safe" or GRAS status.

Mix Calculations for Ice Cream and Frozen Dairy Desserts

The general objective in calculating ice cream mixes is to turn your formula into a recipe based on the ingredients you intend to use and the amount of mix you desire. The formula is given as percentages of fat, milk solids-not-fat, sugar, corn syrup solids (glucose solids), stabilizers and emulsifiers. The ingredients to supply these components are chosen on the basis of availability, quality and cost. The following table illustrates the relationship between the major components, the main ingredients that supply the major components, and the minor components that are supplied with the major ones for each ingredient.

Component and Ingredients to supply that component (but note that each of these ingredients also supplies the following other components):
Milkfat, supplied by Cream (which also supplies SNF and water) or Butter (which also supplies SNF, water);
Milk solids-not-fat (SNF, or sometimes also called serum solids, S.S.), supplied by any of the following:

• Skim powder (which also supplies water, about 3%)
• Condensed skim (which also supplies water)
• Condensed milk (which also supplies water and fat)
• Sweetened condensed (which also supplies water and sugar)
• Whey powder (which also supplies water)

Water, supplied by Skim milk (which also supplies msnf), or milk (which also supplies fat and msnf), or pure water.
Sweetener, supplied by dry or liquid (which also then supplies water) sucrose or corn syrup solids.
The first step in a mix calculation is to identify for each ingredient we intend to use its components. If there is only one source of the component we need for the formula, for example the stabilizer or the sugar, we determine it directly by multiplying the percentage we need by the amount we need, e.g., 100 kg of mix @ 10% sugar would require 10 kg sugar. If there are two or more sources, for example we need 10 % fat and it is coming from both cream and milk, then we need to utilize an algebraic method.
Computer programs developed for mix calculations generally solve a simultaneous equation based on mass and component balances. To solve simultaneous equations, you need as many independent equations as you have unknowns. For an example of a free on-line mix calculator, see http://www.dairyscience.info/newcalculators/calculator/index.php.
For manual calculations, a method known as the "Serum Point" method has been derived. This method has solved the simultaneous equations in a general way so that only the equations need to be known and not resolved each time.
In standardizing mixes, the composition of the various ingredients used must be known. In some cases the percentage of solids contained in a product is taken as constant, while in others the composition must be obtained by analysis. Information on the various ingredients is given below:
(a) Skim milk - can be determined by analysis or assumed at 9 percent serum solids. Fat (0.01% - 0.10%) should be taken into account if significant.
(b) Dried products, e.g. skim milk powder, whey powder, WPC, milk powder blends, usually taken to be 97 percent solids as they retain some moisture.
(c) Cream - Percent fat usually measured by an acceptable method.
Percent MSNF found by formula as follows: (100 - percent fat) x .09 = % snf (assuming that the "skim milk" contains 9% total solids). Example: In cream testing 30% fat, the percent snf would be (100 - 30) x .09 = 6.3% snf
(d) Milk - Percent fat measured by an acceptable method.
Percent snf may be found same as for cream or by making a total solids test and deducting the percent fat.
(e) Condensed Milk Products - Composition of these products should be obtained by the supplier.
(f) Sweeteners - Sucrose - Dry 100% solids
Sucrose - Liquid 66% solids
Dextrose - Dry 100% solids
Corn Syrup Solids 100% solids
Corn Syrup Liquid 80% solids
Glucose 80% solids
Honey 80% solids
(g) Stabilizers and Emulsifiers (if solid) - Because of the small percentage used may be figured as 100 percent solids.
(h) Egg Products - Fresh whole eggs: 10% fat, 25% solids
Fresh egg yolk: 33% fat, 50% solids
Frozen egg yolk: 33% fat, 50% solids
Dried egg yolk: 60% fat, 100% solids

Below are some example problems to look at, if you are interested in the mathematics of mix calculations.

• Example 1. Basic mix using butter, skim powder, and water (only one source of each component). (Algebraic Method)
• Example 2. Mix using cream, skim, and skim powder (three sources of milk SNF, three sources of water). (Algebraic and Serum Point Methods)
• Example 3. Mix using cream, milk, and skim powder (three sources of milk SNF, three sources of water, and two source of fat). (Algebraic and Serum Point Methods)
• Example 4. Mix using cream, milk, and sweetened, condensed skim (three sources of milk SNF, three sources of water, two sources of fat, and two sources of sugar). (Serum Point Method)
• Example 5. Mix using cream, milk, and sweetened, condensed milk (three sources of milk SNF, three sources of water, three sources of fat, and two sources of sugar). (Serum Point Method)
• Example 6. Mix using a given amount of cream and skim, with the balance coming from butter, milk, and skim powder. (Serum Point Method)
• Example 7. Mix using cream, milk, condensed skim, and liquid sweeteners (water needs to be accounted for). (Serum Point Method)

After completing a problem, you should do a proof of your calculation, by ensuring that the mass sums to the desired value, and that the mass fraction of all components also sum to the desired value - see all the examples below. There is only one unique solution, so you know by calculation if you have it right or not!
Note: these are all solved on the basis of 100 kg. If you are making more or less than that, you can still solve on the basis of 100 kg and then scale up or down your answer accordingly, or you can use the desired weight directly in the calculations, but be careful with the serum point method equations - see Example 3 below. If you have scaled up or down from 100 kg, you should do the proof total on the desired weight, and ensure it meets the desired percentage - see Example 3 or 6 below.

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PROBLEM 1

Desired: 100 kg mix testing 14% fat, 10% MSNF, 15% sucrose, 0.4% stabilizer/ emulsifier.

Ingredients on hand: Butter 80% fat, skim milk powder 97% solids, water sucrose, stabilizer/emulsifier.
Solution:
1. Find the amount of butter required to supply 14 kg of fat/ 100 kg mix,
14 kg fat x 100 kg butter/80 kg fat = 17.5 kg butter
2. Find the amount of skim milk powder needed to supply a total of 10 kg of snf/ 100 kg mix.
The butter contributes 17.5 kg butter x 1.8 kg s.s / 100 kg butter = 0.315 kg s.s.
Powder must contribute 10 kg snf - 0.315 kg = 9.685 kg s.s.
9.685 kg snf x 100 kg powder/97 kg snf = 9.98 kg powder
3. Sucrose required will be 15.0 kg/ 100 kg mix.
4. Stabilizer/ emulsifier required will be 0.4 kg/ 100 kg mix.
5. The amount of water required will be equal to 100 minus the sum of the weights of the other ingredients, thus,
100 - (17.5 + 9.98 + 15 + 0.4) = 57.12 kg water
Note: In Problem 1, the serum solids content of the butter was calculated as follows: butter at 80% fat, remaining 20% skim milk at 9% milk solids-not-fat, therefore msnf in butter = 20% x 9% = 1.8%.
In the manufacture of butter, fat is churned from cream (which can be thought of as a mixture of fat and skim milk). If no washing of the butter is performed after churning, the above assumption of 1.8% msnf in 80% fat butter is correct. However, the 20% skim milk could be substituted wholly or in part with wash water, which would reduce the msnf level to anywhere between 1.8% and 0%. Each butter sample either needs to be analyzed for solids or an assumption of no msnf should be made to assure that at least the required msnf is supplied from other ingredients.

PROOF:

Ingredient	Total wt. (kg)	Wt. of Fat (kg)	Wt. of SNF (kg)	Wt. of Total Solids (kg)
Butter	17.50	14.00	0.32	14.32
Skim powder	9.98	--	9.68	9.68
Sucrose	15.00	--	--	15.00
Stabilizer	0.40	--	--	0.40
Water	57.12	--	--	--
Totals	100.00	14.00	10.00	39.40

Note: 14% fat + 10% msnf + 15% sucrose + 0.4% stab. = 39.4% TS

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PROBLEM 2

Desired : 100 kg mix @ 13% fat, 11% MSNF, 15% sucrose, 0.5% stabilizer, 0.15% emulsifier

On hand: Cream @ 40% fat, 5.4% msnf; skimmilk @ 9% msnf; skimmilk powder @ 97% msnf; sugar; stabilizer; emulsifier.
Solution: (Note: only one source of fat, sugar, stabilizer, and emulsifier, but two sources of serum solids)
Cream:
100 kg mix x 13 kg fat/100 kg mix x 100 kg cream/40 kg fat = 32.5 kg cream
Sucrose:
100 kg mix x 15 kg sucrose/100 kg mix = 15 kg sucrose
Stabilizer:
100 kg mix x 0.5 kg stabilizer/100 kg mix = 0.5 kg stabilizer
Emulsifier:
100 kg mix x 0.15 kg emulsifier/100 kg mix = 0.15 kg emulsifier
Algebraic method:
Skim milk and Skim powder, Note: two sources of the MSNF
Now, let x = skim powder, y = skim milk
MASS BALANCE (All the components add up to 100 kg)
x + y = 100 - (32.5 + 15 + 0.5 + 0.15) (1)
MSNF BALANCE (Equal to 11% of the mix and coming from the skim milk, the skim powder, and the cream)
0.97 x + 0.09 y = .11(100) - (.054 x 32.5) (2)
x + y = 51.85 so y = 51.85 - x from (1)
.97 x + .09 y = 9.245 from (2)
.97 x + .09 (51.85 - x) = 9.245 substituting
.97 x - .09 x + 4.67 = 9.245
.88 x = 4.58
x = 5.20 kg skim powder
y = 46.65 kg skim milk
The above shows the solution of a 2-unknown simultaneous equation. Likewise, if there were 3 unknowns, e.g., fat, msnf, and the total weight, then three equations could be written, one for each of fat, msnf, and weight. However, the above problem could also be solved with the Serum Point method, and the example and that solution along with the derivation of the equations follows. The Serum Point calculation assumes 9% msnf in skimmilk and the skim portion of all dairy ingredients. It then solves the calculation beginning with the most concentrated source of serum solids first.
Solution via the serum point method:
1. Amount of powdered skim milk needed is found by the following formula:
(SNF needed - (serum of mix X .09))/(% SNF in powder - 9) X 100 = kg skim powder
This is a generalized equation solved from a mas balance, that works in all situations where milk powder is the most concentrated source of serum solids, and all of the serum products are milk products (i.e., there is no water used in the recipe). An assumption is that the serum fraction of all dairy ingredients contains 9% solids-not-fat, e.g., 40% cream contains 60% skim (100-40), which contains 9% snf, so the snf content of the cream is .60 x .09 = 5.4%
The serum of the mix is found by adding the desired percentages of fat, sucrose, stabilizer and emulsifier together and subtracting from 100. In the present problem then,
100 - (13 + 15 + 0.5 + 0.15) = 71.35 kg serum.
Substituting in the formula we have:
(11 - (71.35 x .09))/(97 - 9) x 100 = 4.58/88 x 100 = 5.20 kg skim powder
2. The weight of cream will be 13 kg x 100 kg cream/40 kg fat = 32.5 kg cream
3. The sucrose will be 15 kg/ 100 kg mix.
4. The stabilizer will be 0.5 kg/ 100 kg mix.
5. The emulsifier will be 0.15 kg/ 100 kg mix.
6. The weight of mix supplied so far is,
Cream 32.50 kg
Skim powder 5.20 kg
Sucrose 15.00 kg
Stabilizer .50 kg
Emulsifier .15 kg
Total 53.35 kg
The skim milk needed therefore is 100 - 53.35 = 46.65 kg.

PROOF:

Ingredient	Total wt. (kg)	Wt. of Fat (kg)	Wt. of SNF (kg)	Wt. of Total Solids (kg)
Cream	32.50	13.00	1.75	14.75
Skim milk	46.65	--	4.20	4.20
Skim milk powder	5.20	--	5.04	5.04
Sucrose	15.00	--	--	15.00
Stabilizer	0.50	--	--	0.50
Emulsifier	0.15	--	--	0.15
Totals	100.00	13.00	11.00	39.64

Note: 13% fat + 11% snf + 15% sucrose + 0.50% stab. + 0.15% emul. = 39.65% TS

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DERIVATION OF THE SERUM POINT EQUATIONS: Let's resolve problem 2 again using simultaneous equations in a general way to show where the serum point equations come from.

On hand: cream @ 40% fat
(supplies fat, water, and serum solids, therefore can be thought of as a mixture of fat and skim milk)
skim milk @ 9% solids not fat
(supplies water and serum solids)
skim milk powder @ 97% solids not fat
(supplies water and serum solids)
sucrose
stabilizer
emulsifier
Solution
- Only one source of fat, sucrose, stabilizer, and emulsifier
kg fat = 100 kg mix x 13 kg fat/100 kg mix = 13 kg fat (The explanation for this assumption becomes clearer in a moment!)
kg sucrose = 100 kg mix x 15 kg sucrose/100 kg mix = 15 kg sucrose
kg stabilizer = 100 kg mix x 0.5 kg stab./100 kg mix = 0.5 kg stabilizer
kg emulsifier = 100 kg mix x 0.15 kg emul./100 kg mix = 0.15 kg emulsifier
- Two sources of serum solids
Let X = skim powder (kg)
Let Y = skim milk (kg) + skim milk in cream (kg)
MASS BALANCE X + Y = Total mix - components already added
X + Y = 100 - (13 + 15 + 0.5 + 0.15), (the "Serum of the Mix")
X + Y = 71.35
(so Y = 71.35 - X)

MSNF BALANCE           0.97X    +       0.09Y   =   (0.11 x 100)

                             "Serum         "Serum         "Serum fraction

                             fraction        fraction         in mix"

                           in powder"      in skim"

0.97 X + 0.09 (71.35 - X) = 11
0.97 X + (0.09 x 71.35) - 0.09 X = 11
0.97 X - 0.09 X = 11 - (0.09 x 71.35)
X = 11 - (.09 x 71.35)/ 0.97 - 0.09
Which is equal to:

        kg skim powder = S.S. needed - (0.09 x serum of mix) x 100

                               % S.S. in powder - 9

X = 4.58/0.88 = 5.20 kg powder

kg cream = 13 kg fat x 100 kg cream/40 kg fat = 32.5 kg cream
kg skim = 100 - 32.5 - 15 - 0.5 - 0.15 - 5.2 = 46.65 kg

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PROBLEM 3

Desired: 100 kg mix containing 18% fat, 9.5% SNF, 15% sucrose, 0.4% stabilizer, 1% frozen egg yolk.

On hand: Cream 30% fat, milk 3.5% fat, skim milk powder 97% solids, sucrose, stabilizer, and egg yolk.
The solution to this problem will be shown by simultaneous equations, since there are three sources of milk SNF, three sources of water, and two source of fat, which require three equations, and by the serum point method. Both produce the same results. Follow whichever method you prefer. Computer programs exist that solve simultaneous equations.
Solution via the algebraic method:
Sucrose: 100 kg mix x 15 kg sucrose/100 kg mix = 15 kg sucrose
Stabilizer: 100 kg mix x 0.4 kg stabilizer/100 kg mix = 0.4 kg stabilizer
Egg yolk: 100 kg mix x 1 kg egg yolk/100 kg mix = 1 kg egg yolk
Now, let x = skim powder, y = milk, z = cream.
MASS BALANCE All the components add up to 100 kg
x + y + z = 100 - (15 + 0.4 + 1) (1)
MSNF BALANCE Equal to 9.5% of the mix and coming from the milk, the skim powder, and the cream; assume 9% in the skim portion of the milk and cream so that the msnf of the milk = .09 x (100 - 3.5) and of the cream = .09 x (100-30)
0.97 x + 0.08685 y + 0.063 z = .095 (100) (2)
FAT BALANCE Equal to 18% of the mix and coming from the milk and cream
.035 y + .3 z = .18 (100) (3)


Solution via the serum point method:
1. Find the amount of skim milk powder required by the following formula:
(SNF needed - (serum of mix x .09))/(% SNF in powder - 9) x 100 = skim powder
Substituting we have,
(9.5 - ( 65.6 x .09 ))/(97-9) x 100 = 3.596/88 x 100 = 4.08 kg powder
2. Amount of sucrose required is 15.0 kg.
3. Amount of stabilizer required is .4 kg.
4. Amount of egg required is 1.0 kg.
5. Find weight of milk and cream needed.
Materials supplied so far are 4.08 kg powder, 15 kg sucrose, 0.4 kg stabilizer, and 1 kg egg yolk, a total of 20.48 kg. 100 - 20.48 = 79.52 kg milk and cream needed.
6. Find the amount of cream by following formula:
((kg fat needed - (kg cream and milk needed x (% fat in milk/100)))/(% fat in cream - % fat in milk)) x 100
substituting we have,
(18 - ( 79.52 x 3.5/100 ))/(30-3.5) x 100 = 15.217/26.5 x 100 = 57.42 kg cream.
7. Amount of milk needed = 79.52 - 57.42 = 22.10 kg of milk.

PROOF:

Ingredient	Total wt. (kg)	Wt. of Fat (kg)	Wt. of SNF (kg)	Wt. of Total Solids (kg)
Cream	57.42	17.23	3.62	20.85
Milk	22.10	0.77	1.92	2.69
Skim milk powder	4.08	--	3.96	3.96
Sucrose	15.00	--	--	15.00
Stabilizer	0.40	--	--	0.40
Egg yolk	1.00	--	--	0.50
Totals	100.00	18.00	9.50	43.40

Note: 18% fat + 9.5% snf + 15% sucrose + 0.40% stab. + 0.50% egg yolk solids (half the egg yolk) = 43.4% TS
If you wanted to make 3000 kg (for example) instead of 100 kg, you could multiply all of the numbers above by 30, or you could set up the equation to solve directly for 3000 kg, as shown below.
Solution via the serum point method for 3000 kg:
1. Find the amount of skim milk powder required by the following formula:
(MSNF needed - (serum of mix x .09))/(% snf in powder - 9) x 100 = skim powder
MSNF needed = 3000 x 9.5% = 285 kg; Serum of the mix = 3000 - 540 (fat) - 450 (sugar) - 12 (stab.) - 30 (egg yolk) = 1968 kg. Substituting we have,
(285 - ( 1968 x .09 ))/(97-9) x 100 = 107.88/88 x 100 = 122.59 kg powder
2. Amount of sucrose required is 3000 x 15% = 450.0 kg.
3. Amount of stabilizer required is 3000 x.4% = 12.0 kg.
4. Amount of egg required is 3000 x 1.0% = 30 kg.
5. Find weight of milk and cream needed.
Materials supplied so far are 122.59 kg powder, 450.0 kg sucrose, 12.0 kg stabilizer, and 30.0 kg egg yolk, a total of 614.59 kg. 3000 - 614.59 = 2385.41 kg milk and cream needed.
6. Find the amount of cream by following formula:
((kg fat needed - (kg cream and milk needed x (% fat in milk/100)))/(% fat in cream - % fat in milk)) x 100
substituting we have,
(540 - ( 2385.41 x 3.5/100 ))/(30-3.5) x 100 = 456.51/26.5 x 100 = 1722.68 kg cream.
7. Amount of milk needed = 2385.41 - 1722.68 = 662.73 kg of milk.

PROOF:

Ingredient	Total wt. (kg)	Wt. of Fat (kg)	Wt. of SNF (kg)	Wt. of Total Solids (kg)
Cream	1722.68	516.8	108.53	625.33
Milk	662.73	23.2	57.56	80.76
Skim milk powder	122.59	--	118.91	118.91
Sucrose	450.00	--	--	450.00
Stabilizer	12.0	--	--	12.0
Egg yolk	30.0	--	--	15.0
Totals	3000.0	540.0	285.0	1302.0

Note: 540/3000 = 18% fat; 285/3000 = 9.5% SNF; 1302/3000 = 43.4% Total solids

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PROBLEM 4

Desired: 100 kgs. mix testing 14% fat, 10% MSNF, 15% sucrose, 0.5% stabilizer/emulsifier.

On hand: Cream 32% fat, milk 3.5% fat, sweetened condensed skim milk 28% serum solids and 40% sugar, sucrose and stabilizer.
Solution via the Serum Point Method :
1. Find amount of condensed skim milk required by the following formula:
(SNF needed - (serum of mix x .09))/( % SNF in cond. - (serum of cond. x .09)) x 100 = sweet cond. skim milk
Note: Serum of condensed is calculated the same as serum of mix, i.e., 100 - (Fat + Sugar + Stab.)
Substituting we have:
(10 - ( 70.5 x .09 ))/(28 - ( 60 x .09 )) x 100 = 16.17 kg cond. skim milk
2. Find amount of sucrose needed:
16.17 x .40 = 6.47 kg of sucrose in the condensed milk.
15 - 6.47 = 8.53 kg of sucrose still needed.
Note: If you added too much sugar by using sweetened condensed skim to supply the desired serum solids, then scale back the sweetened condensed skim to supply all the sugar you need and make up the deficiency in serum solids with skim powder.
3. Amount of stabilizer required is 0.5 kg.
4. Find weight of milk and cream needed.
Material so far supplied is, 16.17 kg condensed milk, 8.53 kg sugar and .5 kg stabilizer, a total of 25.2 kg.
100 - 25.2 = 74.8 kg milk and cream required.
5. Find amount of cream by the following formula:
((kg fat needed - (kg cream and milk needed x (% fat in milk/100)))/(% fat in cream - % fat in milk)) x 100
Substituting we have:
(14 - ( 74.8 x .035 ))/(32 - 3.5) x 100 = 39.93
6. Find milk required:
74.8 - 39.93 = 34.87 kgs. milk.

PROOF:

Ingredient	Total wt. (kg)	Wt. of Fat (kg)	Wt. of SNF (kg)	Wt. of Sugar (kg)	Wt. of Total Solids (kg)
Cream	39.93	12.78	2.44	--	15.22
Milk	34.87	1.22	3.03	--	4.25
Swt. Cond. Milk	16.17	--	4.53	6.47	11.00
Sucrose	8.53	--	--	8.53	8.53
Stabilizer	0.50	--	--	--	0.50
Totals	100.00	14.00	10.00	15.00	39.50

Note: 14% fat + 10% snf + 15% sucrose + 0.5% stab = 39.5% TS

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PROBLEM 5

Desired: 100 kg mix testing 14% fat, 10% MSNF, 15% sucrose, 0.5% stabilizer/ emulsifier.

On hand: Cream 30% fat; milk 4% fat; sweetened condensed whole milk 8% fat, 20% snf, 42% sugar; stabilizer/ emulsifier; and sucrose.
Solution via the Serum Point Method:
1. Find the amount of sweetened condensed milk by formula:
(SNF needed - (serum of mix X .09))/(% SNF in cond. - (% serum in cond. X .09)) X 100 = kg cond. milk
Substituting we have:
(10 - (70.5 X .09))/(20 - (50 X .09)) X 100 = 23.58 kg sweetened cond. milk
2. Stabilizer/ emulsifier required will be 0.5 kg.
3. Find amount of sucrose needed.
23.58 X .42 = 9.90 kg sucrose in cond. milk.
15 - 9.90 = 5.1 kg sucrose still required.
Note: If you added too much sugar by using sweetened condensed skim to supply the desired serum solids, then scale back the sweetened condensed skim to supply all the sugar you need and make up the deficiency in serum solids with skim powder.
4. Find amount of milk and cream needed.
100 - 29.18 (cond. milk, sugar, and stabilizer) = 70.82 kg.
5. Find amount of cream required.
23.58 X .08 = 1.89 kg fat in the condensed milk.
14 - 1.89 = 12.11 kg fat still needed.
Use formula:
((kg fat needed - (kg cream and milk needed x (% fat in milk/100)))/(% fat in cream - % fat in milk)) x 100
Substituting we have:
(12.11 - (70.82 X .04)) / (30 - 4) X 100 = 35.69 kg cream
6. Find amount of milk required:
70.82 - 35.69 = 35.13 kg milk.

PROOF:

Ingredient	Total wt. (kg)	Wt. of Fat (kg)	Wt. of SNF (kg)	Wt. of Sugar (kg)	Wt. of Total Solids (kg)
Cream	35.69	10.71	2.25	--	12.96
Milk	35.13	1.40	3.03	--	4.43
Swt. Cond. Milk	23.58	1.89	4.72	9.90	16.51
Sucrose	5.10	--	--	5.10	5.10
Stabilizer	0.50	--	--	--	0.50
Totals	100.00	14.00	10.00	15.00	39.50

Note: Note: 14% fat + 10% snf + 15% sucrose + 0.5% stab = 39.5% TS

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PROBLEM 6

Desired: Make 2000 kg of mix testing 15% fat, 10.5% MSNF, 15% sucrose, 0.5% stabilizer, 1% egg yolk

From the following: 450 kgs. 30% cream; 300 kgs. skim milk; Get balance from butter @ 84% fat, milk @ 4% fat, skim milk powder, sucrose, stabilizer, and egg yolk.
Solution via the Serum Point Method:
1. Find skim milk powder needed.
Use formula:
(SNF needed - (serum of mix X .09)) / (% snf in powder - 9 ) X 100
Substituting we have:
(210 - (1370 X .09)) / (97 - 9) X 100 = 98.5 kg powder
2. Find sugar, stabilizer, and egg needed.
2000 X .15 = 300 kg sucrose
2000 X .005 = 10 kg stabilizer
2000 X .01 = 20 kg egg yolk
3. List the materials supplied so far:
Cream 450.00 kg
Skim Milk 300.00 kg
Skim Powder 98.50 kg
Sucrose 300.00 kg
Stabilizer 10.00 kg
Egg Yolk 20.00 kg
Total 1,178.50 kg
4. Find amount of butter and milk needed.
2000 - 1178.5 = 821.5 kg butter and milk required.
5. Find amount of fat that still has to be made up:
300 - 135 (Fat in 450 kg 30% cream) = 165 kg
6. Find amount of butter needed by following formula:
((kg fat needed - (kg cream and milk needed x (% fat in milk/100)))/(% fat in cream - % fat in milk)) x 100
Substituting we have:
(165 - (821.5 X .04)) / (84 - 4 ) X 100 = 165.17 kg butter
7. Find amount of milk needed.
821.5 - 165.17 = 656.33 kg milk

PROOF:

Ingredient	Total wt. (kg)	Wt. of Fat (kg)	Wt. of SNF (kg)	Wt. of Total Solids (kg)
Cream	450.00	135.00	28.35	163.35
Milk	656.33	26.25	56.71	82.96
Butter	165.17	138.74	2.37	140.39
Skim Milk	300.00	--	27.00	27.00
Skim milk powder	98.50	--	95.55	95.55
Sucrose	300.00	--	--	300.00
Stabilizer	10.00	--	--	10.00
Egg yolk	20.00	--	--	10.00
Totals	2000.00	300.00	210.00	829.25

Note: 300/2000 = 15% fat; 210/2000 = 10.5% SNF; 829.25/2000 = 41.46% Total solids (= 15% fat + 10.5% snf + 15% sucrose + 0.5% stab + 0.5% egg yolk solids (half of the egg yolk))

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PROBLEM 7 (Using Liquid Sweeteners)

Desired: 100 kgs. of mix testing 12% fat, 11% MSNF, 14% sucrose, 3% corn syrup solids, 0.35% stabilizer, 0.15% emulsifier.

On hand: Cream 40% fat; milk 3.5% fat; condensed skim milk 35% solids; liquid sucrose 66% solids; regular conversion corn syrup 80% solids; stabilizer; emulsifier.
Solution via the Serum Point Method:
1. Calculate the pounds of condensed skim first, but determine serum of the mix as follows:
(a) Find the amount of liquid sucrose that must be added to provide 14 kg of sucrose solids:
14 kg sucrose x 100 kg liq. sucrose/66 kg sucrose = 21.21 kg.
(b) Find the amount of corn syrup that must be added to provide 3 kgs. of corn syrup solids:
3 kg solids x 100 kg liq. css/80 kg solids = 3.75 kg.
Serum of the mix is found by adding together the percentage of fat, liquid sucrose, liquid corn syrup, stabilizer and emulsifier and subtracting from 100:

• 12.00 kg fat
• 21.21 kg liquid sucrose
• 3.75 kg corn syrup
• 0.35 kg stabilizer
• 0.15 kg emulsifier

Total 37.46 kg

100 - 37.46 = 62.54, the serum of the mix
Use formula:
(SNF needed - ( serum of mix x .09 )) / (% SNF in Cond. skim - 9) x 100
Substituting we have:
(11 - ( 62.54 x .09 )) / (35 - 9) x 100 = 20.65 kg of condensed skimmilk
2. Liquid sucrose required = 21.21 kg.
3. Liquid corn syrup required = 3.75 kg.
4. Stabilizer required = 0.35 kg.
5. Emulsifier required = 0.15 kg.
6. Find the amount of milk and cream needed:
100 - (20.65 + 21.21 + 3.75 + 0.35 + 0.15) = 53.89 kg.
7. Find the amount of cream needed by formula:
((kg fat needed - (kg cream and milk needed x (% fat in milk/100)))/(% fat in cream - % fat in milk)) x 100
Substituting we have:
(12 - ( 53.89 x 3.5/100 ))/(40 - 3.5) x 100 = 27.69 kg of cream.
8. Find the amount of milk required:
53.89 - 27.69 = 26.20 kgs. of milk.

PROOF:

Ingredient	Total wt. (kg)	Wt. of Fat (kg)	Wt. of SNF (kg)	Wt. of Sugar (kg)	Wt. of Total Solids (kg)
Cream	27.69	11.08	1.50	--	12.58
Milk	26.20	0.92	2.27	--	3.19
Cond. Skim	20.65	--	7.23	--	7.23
Sucrose	21.21	--	--	14.00	14.00
Corn syrup solids	3.75	--	--	3.00	3.00
Stabilizer	0.35	--	--	--	0.35
Emulsifier	0.15	--	--	--	0.15
Totals	100.00	12.00	11.00	17.00	40.50

Note: 12% fat + 11% snf + 14% sucrose + 3.0% css + 0.35% stab + 0.15% emul. = OVERRUN CALCULATIONS

In looking at calculating overrun in ice cream, it is important to remember the definition of overrun; that is, it is the % increase in volume of ice cream greater than the amount of mix used to produce that ice cream. In other words, if you start off with 1 litre of mix and you make 1.5 litres of ice cream from that, you have increased the volume by 50% (i.e., the overrun is 50%). Equations are as follows:
Figuring plant overrun by volume, no particulates :
% Overrun = (Vol. of ice cream - Vol. of mix used)/Vol. of mix used x 100%
Example : 500 L mix gives 980 L ice cream,
(980 - 500)/500 x 100% = 96% Overrun
80 L mix plus 10 L chocolate syrup gives 170 L chocolate ice cream,
(Note : any flavours added such as this chocolate syrup which become homogeneous with the mix can incorporate air and are thus accounted for in this way : )
(170 - (80 + 10))/(80 + 10) x 100% = 88.8% Overrun

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Figuring plant overrun by volume, with particulates :
Example : 40 L mix plus 28 L pecans gives 110 L butter pecan ice cream,
110 - 28 = 82 L actual ice cream.
% Overrun = (Vol. of ice cream - Vol. of mix used)/Vol. of mix used
= (82 - 40)/40 x 100% = 105%
(Note : The pecans do not incorporate air.)

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Figuring package overrun by weight, no particulates :
% Overrun = (Wt. of mix - Wt. of same vol. of ice cream )/Wt. of same vol. of ice cream x 100%
Must know density of mix (wt. of 1 L), usually 1.09 - 1.1 kg. /L.
(see example below)
Example : If 1 L of ice cream weighs 560 g,
% Overrun = (1090 - 560)/560 x 100% = 94.6% Overrun
(Note : Figuring package overrun by weight if the ice cream has particulates in it gives very little information because both the ratio of ice cream to particulates and the air content of the ice cream affect the final weight.)

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Figuring mix density :
The density of mix can be calculated as follows:
Wt. per litre of water / (% fat/100 x 1.07527) + ((% T.S./100 - % Fat/100) x 0.6329) + (% Water/100) = Wt./ litre mix
Example - Calculate the weight per litre of mix containing 12% fat, 11% serum solids, 10% sugar, 5% corn syrup solids, 0.30% stabilizer, and 38.3% T.S.
1.0 kg/L / ((0.12 x 1.07527) + ((0.383 - 0.12) x 0.6329) + 0.617) = 1.0959 kg/L of mix

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Figuring target package weights, no particulates :
Weight of given vol. of ice cream = Wt. of same vol. of mix / (Desired overrun / 100 + 1)
Example : Desired 90% Overrun, mix density 1.09 kg/L
net wt. of 1 L = 1.09 kg / ( 90/100 + 1) = 573.7 g
Also, density of ice cream = density of mix / (Overrun/100 + 1)
Example: Density of mix 1100 g/L,
@100% Overrun, density of ice cream = 1100 g/L / (100/100 + 1) = 550 g/L

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Figuring target package weights, with particulates :
Example : Butter brickle ice cream; density of mix 1.1 kg/L; overrun in ice cream 100%; density of candy 0.748 kg/L; candy added at 9% by weight, (i.e. 9 kg to 100 kg final product)
In 100 kg final product, we have:
9 kg of candy (or 9 kg / 0.748 kg/L = 12.0 L)
91 kg of ice cream (or 91 kg / (1.1 kg/L / (100/100 + 1)) = 165.4 L)
So, 100 kg gives a yield of 12 + 165.4 = 177.4 L
1 L weighs 100 kg / 177.4 L = 564 grams
(Note : In many cases, ice cream of different flavours is frozen to the same weight. As a result, overrun of actual ice cream in product varies.)

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Developing an Overrun Table for Use When Manufacturing Ice Cream:
To develop an overrun table to determine overrun quickly by weight when making ice cream, all you need is a cup with a fixed volume that is convenient for filling ice cream into (like a steel measuring cup, for example, with a flat top that would be easy to scrape level) and an ordinary gram balance. Then, using the equation from above, you can calculate what the weight of the cup would be for a series of different overruns, and then make up a table. Then when you are running ice cream, just keep weighing the cup and checking against the table for the overrun in the cup.
% Overrun = (Wt. of mix - Wt. of same vol. of ice cream )/Wt. of same vol. of ice cream x 100%
So, lets say your cup holds 100 mL. Fill the cup with mix and weigh it. Let's say the net weight (minus the weight of the empty cup) is 110 g. Lets say the empty cup weighs 30 g.
The net weight of the cup at 5% overrun would be:
.05 = (110 - x)/x, solve for x and you get 104.8, so the gross weight would be 134.8 g.
{In case your algebra is rusty, to solve for x, follow this example:
.05 = (110-x)/x
x = (110-x)/.05
x = 110/.05 - x/.05
x = 2200 - 20x
x + 20x = 2200
21x = 2200
x = 2200/21 = 104.76}
Likewise for 10%, 0.1 = (110 - x)/x, solve for x and you get 100, so the gross weight would be 130 g.
Keep going up to 150% or so, then make a table:

Overrun%           Weight of cup + ice cream (grams)

0                  140

5                  134.8

10                 130

.

.

. 

150                 74

40.5% TS

Structure of Ice Cream

Ice cream structure is both fascinating and confusing. The way we perceive the texture of ice cream when we consume it (smooth, coarse, etc.) is based on its structure, and thus structure is probably one of its most important attributes.

Colloidal aspects of structure

Please look at

this diagram of the fat structure in ice cream
when reading the following description, and try to put the two together in your mind. Also, please look at the last paragraph of this page for links to electron micrographic images of the structure of ice cream.
Ice cream is both an emulsion and a foam. The milkfat exists in tiny globules that have been formed by the homogenizer. There are many proteins that act as emulsifiers and give the fat emulsion its needed stability. The emulsifiers are added to ice cream to actually reduce the stability of this fat emulsion by replacing proteins on the fat surface, leading to a thinner membrane more prone to coalescence during whipping. When the mix is subjected to the whipping action of the barrel freezer, the fat emulsion begins to partially break down and the fat globules begin to flocculate or destabilize. The air bubbles which are being beaten into the mix are stabilized by this partially coalesced fat. If emulsifiers were not added, the fat globules would have so much ability to resist this coalescing, due to the proteins being adsorbed to the fat globule, that the air bubbles would not be properly stabilized and the ice cream would not have the same smooth texture (due to this fat structure) that it has.

Effect of emulsifier on fat destabilization in ice cream 17 KB
This fat structure which exists in ice cream is the same type of structure which exists in whipped cream. When you whip a bowl of heavy cream, it soon starts to become stiff and dry appearing and takes on a smooth texture. This results from the formation of this partially coalesced fat structure stabilizing the air bubbles. If it is whipped too far, the fat will begin to churn and butter particles will form. The same thing will happen in ice cream which has been whipped too much.

Ice Cream Meltdown

One of the important manifestations of ice cream structure is its melt-down. When you put ice cream in an ambient environment to melt (as in a scoop on a plate), two events occur; the melting of the ice and the collapse of the fat-stabilized foam structure. The melting of the ice is controlled by the outside temperature (fast on a hot day) and the rate of heat transfer (faster on a hot, windy day). However, even after the ice crystals melt, the ice cream does not "melt" (collapse) until the fat-stabilized foam structure collapses, and that is a function of the extent of fat destabilization/partial coalescence, which is controlled mostly by the emulsifier concentration, for reasons we have just described above.

This is shown in the diagram below, which shows ice cream sitting on a mesh screen at ambient temperature:

You can see above the increased amount of shape retention and slowness of melt that comes from the added emulsifiers, particularly polysorbate 80.

Structure from the Ice crystals

Also adding structure to the ice cream is the formation of the ice crystals. Water freezes out of a solution in its pure form as ice. In a sugar solution such as ice cream, the initial freezing point of the solution is lower than 0° C due to these dissolved sugars (freezing point depression), which is mostly a function of the sugar content of the mix. As ice crystallization begins and water freezes out in its pure form, the concentration of the remaining solution of sugar is increased due to water removal and hence the freezing point is further lowered. This process is shown here, schematically.

This process of freeze concentration continues to very low temperatures. Even at the typical ice cream serving temperature of -16° C, only about 72% of the water is frozen. The rest remains as a very concentrated sugar solution. Thus when temperature is plotted against % water frozen, you get the phase diagram shown below. This helps to give ice cream its ability to be scooped and chewed at freezer temperatures. The air content also contributes to this ability, as mentioned in discussing overrun.

The effect of sweeteners on freezing characteristics of ice cream mixes is demonstrated by the plot shown on the ice cream freezing curve.
Also critical to ice cream structure is ice crystal size, and the effect of recrystallization (heat shock, temperature fluctuations) on ice crystal size and texture. A primer on the theoretical aspects of freezing will help you to fully understand the freezing process. Please see the discussion and diagram on ice crystallization rate, as shown on that page, to fully understand this process. Recrystallization (growth) of ice is discussed elsewhere in the context of shelf life.
Thus the structure of ice cream can be described as a partly frozen foam with ice crystals and air bubbles occupying a majority of the space. The tiny fat globules, some of them flocculated and surrounding the air bubbles also form a dispersed phase. Proteins and emulsifiers are in turn surrounding the fat globules. The continuous phase consists of a very concentrated, unfrozen solution of sugars. One gram of ice cream of typical composition contains 1.5 x 10exp12 fat globules of average diameter 1µ m that have a surface area of greater than 1 square meter (in a gram!), 8 x 10exp6 air bubbles of average diameter 70 µ m with a surface area of 0.1 sq. m., and 8 x 10exp6 ice crystals of average diameter 50 µ m with a surface area of another 0.1 sq. m. The importance of surface chemistry becomes obvious!

Microscopy

Before we leave ice cream structure, I want to draw your attention to the following address: "Foods Under the Microscope". This is a link to an absolutely marvelous website developed by my good friend Dr. Milos Kalab, with many high-quality images of the structure of milk and dairy products obtained during Dr. Kalab's long and outstanding career as a food microscopist with Agriculture and Agri-Food Canada in Ottawa. Dr. Kalab asked me to contribute microscopic images of ice cream structure as a guest microscopist. You can find my (Doug Goff) first contribution under "Guest microscopists", and I have also copied it here. Subsequent to that submission, I have prepared another one for D. Kalab that focuses on the use of cryo-fixation and TEM for visualization of fat and air structures in ice cream. One of my graduate students, Alejandra Regand, also made a contribution, based on her M.Sc. thesis work, focusing on the structure of polysaccharides in frozen solutions.

Ice cream structure is an active area of our research here at the University of Guelph. Please see my publications for more details of our research.

Theoretical Aspects of the Freezing Process

The Process of Crystallization
This section will briefly review the physico-chemical processes that occur during a freezing process. The figure below shows the time-temperature relationship for freezing of pure water (ABCDE) and aqueous solutions (AB'C'D'). The first thermal event that can be seen from such a diagram is undercooling below the freezing point before the induction of crystallization, from A to B or B' . This is a non-equilibrium, metastable state which is analogous to an activation energy necessary for the nucleation process. Pure water can be undercooled by several degrees before the nucleation phenomenon begins.

Once the critical mass of nuclei is reached, the system nucleates at point B or B' in the figure and releases its latent heat faster than heat is being removed from the system. In aqueous solutions, however, B' is not as low as B, since the added solute will promote heterogeneous nucleation, thereby accelerating the nucleation process. The temperature increases instantly to the initial freezing temperatureof the solution at Point C (0oC) or C' (Tf). The presence of solutes results in depression of the freezing point based on Raoult's Law, which relates vapor pressure of the solution to that of pure solvent based on solute concentration. Note that C' is not as high as C, because the initial freezing point is depressed as a result of the solute. Hence, the solute has greatly decreased the amount of undercooling for two reasons: faster nucleation and lowered freezing point. In very concentrated solutions, it is sometimes even difficult to induce undercooling.
In pure water, the time line from C to D in the figure reflects the time during which crystal growth is occurring at 0oC. Fast freezing rates promote the formation of many small ice crystals during this period. The partially frozen mixture will not cool until all of the "freezable" water has crystallized; hence, the line CD for pure water occurs at constant temperature. The freezing time is usually defined as the time from the onset of nucleation to the end of the crystal growth phase. After crystallization is completed, the temperature drops from D to E as sensible heat of ice is removed.
During the freezing of the aqueous solution, a freeze-concentration process occurs as water freezes out of solution in the form of pure ice crystals (C'D'), effectively removing solvent from the solute. Hence the freezing temperature of the remaining solution continues to drop. At temperatures well below the initial freezing point, some liquid water remains. Also, a large increase in the viscosity of the unfrozen phase occurs, thus decreasing the diffusion properties of the system and hindering crystallization. It is more difficult to assign a freezing time to this process, but it is usually taken as the time to reach some predetermined temperature below the initial freezing point. This freeze-concentration process establishes the freezing curve.

Importance of Crystallization Rate

The freezing curve predicts the amount of ice at any given temperature, which is a function of freezing point depression and hence the number of solutes (concentration of sugar, etc.). It doesn't predict anything about ice crystal size. What predicts ice crystal size is the rate of freezing - the faster the rate - the more nucleation is promoted, and the greater number of crystals of smaller size that will result. This is very important in terms of ice cream structure.

Importance of Temperature Fluctuations and Re-Crystallization

Mechanisms of ice recrystallization

Ice crystals formed after scraped-surface freezing and hardening of ice cream are unstable and will undergo recrystallization, the extent of which depends in part on how effectively the system has been stabilized. See also the discussion regarding ice cream shelf-life, where I have included some images to show the effects of recrystallization on ice crystals in ice cream. Recrystallization is the process of changes in number, size and shape of ice crystals during frozen storage, although the amount of ice stays constant with constant temperature throughout this process (dictated by the equilibrium freezing curve). Recrystallization basically involves small crystals disappearing, large crystals growing and crystals fusing together.

There are several types of recrystallization processes. Iso-mass recrystallization ("rounding off") refers to changes in surface or internal structure so that crystals with irregular shapes and large surface-to-volume ratios assume a more compact structure. In other words, sharper surfaces are less stable than flatter ones and will show a tendency to become smoother over time. Migratory recrystallization refers in general to the tendency of larger crystals to grow at the expense of smaller crystals. Ostwald ripening refers to migratory recrystallization that occurs at constant temperature and pressure due to differences in surface energy between crystals, most likely involving melting-diffusion-refreezing or sublimation-diffusion-condensation mechanisms. However, migratory recrystallization is greatly enhanced by temperature fluctuations (heat shock) inducing a melt-refreeze behavior due to ice content fluctuations. Melt-refreeze behavior can lead to complete disappearance of smaller crystals during warming and growth of larger crystals during cooling, or to a decrease in size of crystals during partial melting and regrowth of existing crystals during cooling. Melt-refreeze should occur to a greater extent at higher temperatures and more rapidly for smaller crystals. Accretion refers to a natural tendency of crystals in close proximity to fuse together; the concentration gradients in the areas between them are high, thus, material is transported to the point of contact between crystals and a neck is formed. Further "rounding off" will occur because a high curvature surface like this has a natural tendency to become planar.

Formation of the Glassy Phase in Frozen Foods

During the freezing of foods, ice is formed as pure water goes through the two-step (nucleation and propagation) crystallization process. As temperature decreases and water is removed from a food in the form of ice, the solutes present in the UFP are freeze-concentrated. An equilibrium freezing temperature exists for each ice/UFP ratio, which is a function of the solute concentration. This equilibrium thermodynamic process can be modelled on a phase diagram as an equilibrium freezing (liquidus) curve (see figure below), which extends from the melting temperature (Tm) of pure water (0oC) to the eutectic temperature (Te) of the solute, the point at which the solute has been freeze-concentrated to its saturation concentration.
As temperature is lowered, it is highly unlikely that solute will crystallize at Te, due to high viscosity from concentration of solute and low temperature, so that freeze-concentration proceeds beyond Te in a non-equilibrium state. The highly-concentrated UFP can then go through a viscous liquid/glass state transition, driven by the reduction in molecular motion and diffusion kinetics as a result of both the very high concentration and low temperature.
A glass is defined as a non-equilibrium, metastable, amorphous, disordered solid of extremely high viscosity (ie., 10 exp10 to 10 exp14 Pa.s), also a function of temperature and concentration. The glass transition curve extends from the glass transition temperature (Tg) of pure water (-134oC) to the Tg of pure solute. The equilibrium phase diagram and the kinetically-derived state diagram can be modelled together on a supplemented state diagram. The supplementary state diagram showing the solid/liquid coexistence boundaries and glass transition profile for a binary sucrose/water system is shown in the figure below. Below and to the right of the glass transition line, the solution is in the amorphous glass state, with or without ice present depending on temperature and freezing path followed, while above and to the left of the glass transition line, the solution is in the liquid state, with or without ice depending on temperature.

As an example, assume a sucrose solution with an initial concentration of 20% at room temperature (point A). The initial Tg of this solution at room temperature before phase separation is marked as point B (if the solution could be undercooled to this temperature without ice formation). However, upon slowly cooling of the system somewhat below its equilibrium freezing point (due to undercooling), nucleation and subsequent crystallization begins at point C and initiates the freeze-concentration process, removing water in its pure form as ice. As ice crystallization proceeds, the continual increase in solute concentration (removal of water) further depresses the equilibrium freezing point of the UFP in a manner which follows the liquidus curve (shown as path C) while the Tg of the UFP moves up the glass transition line (path B; due to increased concentration) with a rapid increase in viscosity in a non-Arrhenius manner, particularly in late stages of the freezing process.
Co-crystallization of solute at the Te is unlikely and thus freeze-concentration continues past Te into a non-equilibrium state since the solute becomes superstaurated. When a critical, solute-dependent concentration is reached, the unfrozen liquid exhibits very resisted mobility and the physical state of the UFP changes from a viscoelastic liquid to a brittle, amorphous solid glass.
The intersection of the non-equilibrium extension of the liquidus curve, beyond Te, and the kinetically-determined glass transition curve, point D in the above figure, represents the solute-specific, maximally freeze-concentrated Tg of the frozen system, denoted Tg', where ice formation ceases within the time-scale of the measurement. The corresponding maximum concentrations of water and sucrose "trapped" within the glass at Tg' and unable to crystallize are denoted the Wg' and Cg' , respectively. It is worth noting that this unfrozen water is not bound in an "energetic" sense, rather unable to freeze within practical time frames.
At the Tg', the supersaturated solute takes on solid properties because of reduced molecular motion, which is responsible for the tremendous reduction in translational, not rotational, mobility. It is this intrinsic slowness of molecular reorganization below Tg' that the food technologist seeks to create within the concentrated phase surrounding constituents of food materials.
However, warming from the glassy state to temperatures above the Tg' results in a tremendous increase in diffusion, not only from the effects of the amorphous to viscous liquid transition but also from increased dilution as melting of small ice crystals occurs almost simultaneously (Tg' = Tm'). The time-scale of molecular rearrangement continually changes as the Tg is approached, so that food technologists can also gain some enhanced stability at temperatures above Tg' by minimizing the delta T between the storage temperature and Tg' , either by reduced storage temperatures or enhaced Tg' through freezing methods or formulation. Hence, knowledge of the glass transition provides a clear indication of molecular diffusion and reactivity, and therefore, shelf-stability.
Formation of a Dilute Glass
Despite the thermodynamic driving force to achieve the unfrozen water content corresponding to Wg', one must also consider the large kinetic factors which "overtake" the freezing process. At sub-zero temperatures, the formation of an amorphous state is time-dependent since the limiting factor of the process (water removal in the form of ice) becomes more difficult as concentration increases. The exponential effect of viscosity on mass transfer properties acts as the limiting factor for growth. In addition, under conditions where heat removal is rapid, a high level of undercooling at the interface will only add to a further decrease in propagation rate. The net result is that freezing becomes progressively slower as ice crystallization is hindered and consequently more time is required for lattice growth at each temperature.
Therefore the kinetic restriction imposed on the system can lead to a situation in which non-equilibrium freezing, resulting in a partial dilute glass, can occur. The typical pathway a system may follow during non-equilibrium freezing is shown in the above figure as the line leading to lower Tg (path E) than Tg' with a corresponding lower sucrose concentration in the glass (Cg) and higher water content in the glass (Wg) due to excess undercooled water plasticized within the glass. This is often referred to as a dilute glass. The magnitude of deviation from the equilibrium curve, and hence the actual path followed, may be regarded as a function of the degree of departure from equilibrium.
Systems possessing this undesirable structure may undergo various relaxation-recrystallization mechanisms in order to maximally freeze-concentrate and minimize the unfrozen water content. As a result, during warming, systems formed under these conditions may lead to one or more low temperature transitions, followed by an exothermic devitrification peak due to crystallization of immobilized water, and finally the onset of ice melting, Tm.
Ice crystallization, recrystallization and glass transitions are active areas of our research here at the University of Guelph. Please see my publications for more details of our research.

Ice Cream Shelf-Life

The most frequently occurring textural defect in ice cream is the development of a coarse, icy texture. Iciness is also the primary limitation to the shelf life of ice cream and probably also accounts for countless lost sales through customer dissatisfaction with quality. There is no answer to the question "What is the shelf-life of ice cream?", it depends entirely on its conditions of storage. It might be one year, or it might be two weeks or less. Although the source of and the contributing factors to the problem of icincess are well known, it is also one of the defects about which I am most often asked.
Processor's have known for a long time how to prevent iciness and the answer is still the same: formulate the ice cream properly to begin with, freeze the ice cream quickly in a well-maintained barrel freezer, harden the ice cream rapidly, and avoid as much as possible temperature fluctuations during storage and distribution. Ice crystals need to be numerous and of small, uniform size so they are not detected when eaten. It is heat shock, large temperature fluctuations, which is the greatest culprit to the loss of these small, uniform ice crystal size distributions and resulting coarse, icy texture. Perhaps it is time another message was added to the prevention of iciness and that is to educate the retailer's and the consumer about the causes of iciness and preventative action to maintain a smooth-textured ice cream.
Before we begin looking specifically at shelf-life, you need to re-acquaint yourself with the freezing aspects of ice cream manufacturing, the structure of ice crystals in ice cream, and the theoretical aspects of the freezing process.

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Temperature Fluctuations and Ice Recrystallization

Ice crystals are relatively unstable, and during frozen storage, they undergo changes in number, size, and shape, known collectively as recrystallization. This is probably the most important reaction leading to quality losses in all frozen foods. Some recrystallization occurs naturally at constant temperatures, but by far the majority of problems are created as a result of temperature fluctuations. If the temperature during the frozen storage of ice cream increases, some of the ice crystals, particularly the smaller ones, melt and consequently the amount of unfrozen water in the serum phase increases. Conversely, as temperatures decrease, water will refreeze but does not renucleate. Rather, it is deposited on the surface of larger crystals, so the net result is that the total number of crystals diminish and the mean crystal size increases. Temperature fluctuations are common in frozen storage as a result of the cyclic nature of refrigeration systems and the need for automatic defrost. However, mishandling of product is probably the biggest culprit. The sight of ice cream sitting unrefrigerated on a loading dock, in the supermarket aisle, in a shopping cart, or in someone's grocery bag is too common. If one were to track the temperature history of ice cream during distribution, retailing, and finally consumption, one would find a great number of temperature fluctuations. Each time the temperature changes, the ice to serum content changes, and the smaller ice crystals disappear while the larger ones grow even larger. Recrystallization is minimized by maintaining low and constant storage temperatures.
The graph below provides data to show the increase in size of ice crystals that occurs with temperature cycles (from the work of A. Flores and H. D. Goff).







Below are several cryo-scanning electron micrographic images of ice cream after temperature fluctuations. In the first composite, all pictures are at the same magnification, the top two are fresh, the botton two are heat-shocked. You can see the tremendous increase in crystals size that has occurred. The next image shows an example of accretion, where crystals fuse as they grow.

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The Role of Stabilizers

The ice cream stabilizers, locust bean gum, guar gum, carboxymethyl cellulose, sodium alginate, carrageenan, and xanthan, are a group of ingredients used commonly in ice cream formulations. They are usually integrated with the emulsifiers in proprietary blends. The primary purposes of using stabilizers in ice cream are to produce smoothness in body and texture, retard or reduce ice and lactose crystal growth during storage, and to provide uniformity of product and resistance to melting. Additionally, they stabilize the mix to prevent wheying off, produce a stable foam with easy cut-off at the barrel freezer and slow down moisture migration from the product to the package or the air. The action of the polysaccharides in ice cream result from their ability to form gel-like structures in water and to hold free water. Control of iciness by stabilizers has been attributed to a reduction in the growth of ice crystals over time, probably related to a reduction in water mobility as water is entrapped by their entangled network structures in the serum phase. Proper formulation with stabilizers designed to combat against heat shock is an almost essential defense against the inevitable growth of ice crystals. Low total solids mixes are also more difficult to effectively stabilize as the increased content of water leads to more ice at any given temperature. Also, high concentrations of sugars or lactose will change the ratio of water to ice and lead to greater problems of recrystallization.
Stabilizer functionality in ice cream is an active area of our research here at the University of Guelph. Please see the work of one of my graduate students, Alejandra Regand, in this area, based on her M.Sc. thesis work, which focusses on the structure of polysaccharides in frozen solutions. Please also see my publications for more details of our research.

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Education needed

I hope I have stimulated ice cream processor's to begin an education campaign for ice cream retailer's and consumer's about the subject of heat shock and coarseness. I often hear processor's say that handling of the product after it leaves their hands is out of their control. Do not forget, however, that the consumer is buying your label of product. The quality they receive is a reflection on you, despite where the damage occurred. The people unloading or stocking your ice cream, and the customer who buy's your ice cream cannot be expected to understand the concepts of ice crystal size distributions and ice crystal growth without a little help from you. Ice cream is unlike the other frozen foods they handle routinely and this must be explained to them. We often sell ice cream at the University of Guelph. The majority of our customer's comment on the superb texture of our ice cream. They often ask us what we do differently from other manufacturer's to produce an ice cream that is so smooth. Although we would like to take credit for some great revelation in processing, the difference is that they are buying ice cream that is fresh, directly from our hardening room. If customer's were buying ice cream from the hardening room's of all manufacturer's, no doubt you would get the same comments, but they are not.
That is why I am suggesting some education to retailer's and consumer's on the subject may be of benefit to both them and you. An information package to retailer's on proper handling of ice cream may be very welcome so that they can use it in their training of new and continuing employees. The IICA in Washington has prepared material for this purpose. Consumer's can be contacted through side panels on ice cream packages or through point of purchase displays. Whatever the media, the message is that both retailer's and consumer's can play an important role in maintaining the texture in ice cream which is desired.

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Maintaining Shelf-life

o Formulate the ice cream properly
- Freezing point depression and sugar considerations
- Stabilizers
o Freeze the ice cream quickly in a well-maintained barrel freezer
- Continuous freezers with high rates of heat exchange
- Free of fouling (eg., oil) on refrigerant side
- Blades with a good, even edge
- Short, insulated process lines through ingredient feeder, packaging equipment
- Precooling of ingredients
o Harden the ice cream rapidly
- High rates of heat transfer: convection (high ΔT and forced air with free air flow) or conduction
- Importance of thermal centre and shrink-wrapping of bundles
o Avoid temperature fluctuations during storage and distribution
- Importance of low, constant temperatures
- Avoid mishandling at all stages
o Educate retailers and consumers about shelf stability
-Mishandling is usually not at the manufacturing level but quality losses affect consumer acceptance of your product

Ice Cream Flavours

• Introduction
• Vanilla
• Chocolate and Cocoa
• Fruit Ice Cream
• Nuts in Ice Cream
• Colour in Ice Cream

Introduction

Most ice cream is purchased by the consumer on basis of flavour and ingredients. There are many different flavours of ice cream manufactured, and to some extent limited only by imagination. Vanilla accounts for 30% of the ice cream consumed. This is partly because it is used in so many products, like milkshakes, sundaes, banana splits, in addition to being consumed with pies, desserts, etc.

It is the ice cream manufacturers responsibility to prepare an excellent mix, but often they put the responsibility of the flavours and ingredients on the supplier.

US Ice Cream Consumption by Flavour, 2006

                                          percentage of volume

 1.     Vanilla                                 30.2

 2.     Chocolate                               10.0

 3.     Chocolate Chip                           5.7  

 4.     Butter Pecan                             4.0 

 5.     Strawberry                               3.7

 6.     Neapolitan                               3.0

 7.     Cookies and cream                        2.6

 8.     Rocky Road                               1.9

 9.     Cookie Dough                             1.5

10.     Cherry Vanilla                           0.9

11.     Coffee                                   0.7

Source:  Dairy Facts, 2007, International Dairy Foods Association

Ingredients are added to ice cream in four ways during the manufacturing process:

1. Mix Tank: for liquid flavours, colours, fruit purees, flavored syrup bases Ð anything that will be homogeneously distributed in the frozen ice cream.
2. Variegating Pump: for ribbons, swirls, ripples, revels
3. Ingredient Feeder: for particulates - fruits, nuts, candy pieces, cookies, etc., some complex flavours may utilize 2 feeders
4. Shaker table: for large inclusions

Generally, the delicate, mild flavours are easily blended and tend not to become objectionable at high concentrations, while harsh flavours are usually objectionable even in low concentrations. Therefore, delicate flavours are preferable to harsh flavours, but in any case a flavour should only be intense enough to be easily recognized. Flavouring materials may be:

1. Natural
2. Artificial or imitation
3. Blends of the two

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Vanilla

Vanilla is without exception the most popular flavour for Ice Cream in North America. The dairy industry uses half of the total imported vanilla to North America. It is a very important ice cream ingredient, not only in vanilla ice cream, but in many other flavours where it is used as a flavour enhancer, e.g. chocolate much improved by presence of vanilla.

Vanilla comes from a plant belonging to the orchid family called Vanilla planifolia. There are several varieties of vanilla beans among which are Bourbon, Tahitian, Mexican. Bourbon beans are used to produce best vanilla extracts. Bourbons from Madagescar are the finest and account for over 60% of World production, Indonesia, 23% (UN FAO 2005).
From each blossom of the vine that is successfully fertilized comes a pod which reaches 6-10 inches in length, picked at 6-9 months. It requires 26-29oC day and night throughout the season, and frequent rains with dry season near end for development of flavour.
Pods are immersed in hot water to "kill them" (also increases enzyme activity), then fermented for 3-6 months by repeated wrapping in straw to "sweat" and then uncovered to sun dry. 5-6 kg green pods produce 1 kg. cured pods. Beans then aged 1-2 yrs. Enzymatic reactions produce many compounds - vanillin is the principal flavour compound. However, there is no free vanillin in the beans when they are harvested, it develops gradually during the curing period from glucosides, which break down during the fermentation and "sweating" of the beans. Extraction takes place as the beans are chopped (not ground) and placed in stainless steel percolator and warm alcohol (50oC, 50% solution) is pumped over and through the beans until all flavouring matter is extracted.
Concentrated Extract
Vacuum distillation takes place for a large part of the solvent. The desired concentration is specified as two fold, four fold, etc. Each multiple must be derived from an original 13.35 oz. beans.
Vanilla can be and is produced synthetically to a large extent. By-product of pulp and paper industry (lignan) or petrochemical industry (guaiacol). Compound flavours are produced from combination of vanilla extract and vanillin. Vanillin maybe added at one ounce to the fold and labelled Vanilla-Vanillin Flavour. Number of folds plus number oz. of vanillin equal total strength, eg. 2 fold + 2 oz. = 4 fold vanilla-vanillin. However,more than 1 oz to the fold is deamed imitation.
Vanilla flavouring is available in liquid form as:

• Natural Vanilla
• Natural and artificial (reinforced Vanilla with Vanillin)
• Artificial Vanilla (vanillin)

Usage level in the mix is a function of purity and concentration, usually ~0.3%.

Some vanillin actually improves flavour over pure vanilla extract but too much vanillin results in harsh flavours.
The choicest of ice creams can be made only with the best of flavouring materials. A good vanilla enhances the flavour of good dairy products in ice cream. It does not mask it.

Chocolate and Cocoa

The cacao bean is the fruit of the tree Theobroma cacao, (Cacao, food of the gods) which grows in tropical regions such as Mexico, Central America, South America, West Indies, African West Coast. The word cocoa is a corruption of the native word cacao. The beans are embedded in pods on the tree, 20-30 beans per pod. When ripe, the pods are cut from the trees, and after drying, the beans are removed from the pods and allowed to ferment, 10 days (microbiological and enzymatic fermentation). Beans then are washed, dried, sorted, graded and shipped.

At the processing plant, beans are roasted, seed coat removed - called the nib. The nib is ground, friction melts the fat and the nibs flow from the grinding as a liquid, known as chocolate liquor.

Liquor:

55% fat, 17% carbohydrate, 11% protein, 6% tannins and many other compounds (bitter chocolate - baking).

Cocoa butter:

fat removed from chocolate liquor, narrow melting range 30 to 36° C

Cocoa:

after the cocoa butter is pressed from the chocolate liquor, the remaining press cake is now material for cocoa manufacture

The amount of fat remaining determines the cocoa grade:

• medium fat (Breakfast) cocoa 20-24% fat
• low fat 10-12% fat

Cocoa powder can also be alkalized, which reduces acidity/astringency and darkens the colour. Slightly alkalized cocoa is usually preferred in ice cream because it gives a deeper colour but the choice depends upon:

• consumer preference
• desired color (Blackshire cocoa may be used to darken color)
• strength of flavour
• fat content

There are many types of chocolate that differ in the amounts of chocolate liquor, cocoa butter, sugar, milk, other ingredients, and vanilla.

Imitation chocolate

replacing some or all of the cocoa fat with other vegetable fats. Improved coating properties, resistance to melting

White chocolate

cocoa butter, MSNF, sugar, no cocoa or liquor

In chocolate ice cream manufacture, cocoa is more concentrated for flavouring than chocolate liquor (55% fat) because cocoa butter has relatively low flavour. However, the cocoa fat adds texture to the ice cream. Acceptable mixes can be made using 3% cocoa powder, 2.5% cocoa powder plus 1.5% chocolate liquor, or 5% chocolate liquor.

A good chocolate ice cream will be made if the cocoa and/or chocolate liquor is added to the vat and homogenized with the rest of the mix. Chocolate mixes have a tendency to become excessively viscous so stabilizer content and homogenizing pressure need to be adjusted.
One problem is called chocolate specking. It can occur in soft serve ice cream, when cocoa fibres become entrapped in the churned fat.

Fruit Ice Cream

Fruit for Ice Cream is available in the following forms:

1. Fresh Fruit
2. Raw Frozen Fruit
3. Open Kettle Processed Fruit
4. Aseptically Processed Fruit

Advantages of processed fruits:

1. Purchasing year round supply: problems of procurement and storage transferred to fruit processor
2. Availability: blending of sources from around the world in RTU form, no thawing, straining, etc.
3. Quality control: processor adjusts for quality variations
4. Ice Cream quality: fruit won't freeze in ice cream, usually free of debris, straw, pits.
5. Microbial Safety
6. Convenience

Fruit feeders are used with continuous freezers to add the fruit pieces, while any fruit juice is added directly to the mix. Fruit is usually added at about 15-25% by weight.

Nuts in Ice Cream

Nuts are usually added at about 10% by wt. Commonly used are walnuts, pecans, filberts, almonds and pistachios. Brazil nuts and cashews have been tried without much success.

Quality Control of Nutmeats for Ice Cream

1. Extraneous and Foreign Material:
   Requires extensive cleaning, Colour Sorter, Destoner, X-rays, Aerator, Hand-Picking, Screening
2. Microbiological Testing:
   Aflatoxin contamination can be a hazard with Peanuts, Pistachios, Brazils. All nutmeats should receive random testing for: Standard Plate Count, Coliform, E. Coli, Yeast and Mold, Salmonella.
3. Bacteria Control:
   Nuts must be processed in a clean sanitary premise following good manufacturing practices. Nuts should be either oil roasted or heat treated to reduce any bacteria.
4. Sizing:
   Some nutmeats require chopping to achieve a uniform size in order to fit through the fruit feeder, i.e.: Pecans, Almonds, Peanuts, Filberts
5. Storage Nutmeats should be stored at 34-38° F to maintain freshness and reduce problems with rancidity.

Colour in Ice Cream

Ice cream should have a delicate, attractive colour that suggests or is closely associated with its flavour. Almost all ice creams are slightly coloured to give them the shade of the natural product 15% fruit produces only a slight effect on colour. However, most suppliers, would include some colour in the fruit to save the processor time i.e. solid pack strawberries include colour. Most colours are of synthetic origin, must be approved, purchased in liquid or dry form. Solutions can easily become contaminated and therefore must be fresh.

Colours are used in ice cream to create appeal. If used to excess they indicate cheapness. The choice of shade is dictated by flavour, i.e. red for strawberry, light green for mint, purple for grape, etc.

Ice Cream Defects

If you haven't already done so, check out the Milk Grading and Defects section for a mini-introduction to the senses. This section will cover the following topics:

·         Flavour Defects

·         Body and Texture Defects

·         Melting Quality Characteristics

·         Colour Defects

·         Shrinkage Defect

Flavour Defects

Can be classified according to the flavouring system (lacks flavour or too high flavour, unnatural flavour), the sweetening system (lacks sweetness or too sweet), processing related flavour defects (cooked), dairy ingredient flavour defects (acid, salty, old ingredient, oxidized/metallic, rancid, or whey flavours), and others (storage/absorbed, stabilizer/emulsifier, foreign). Some details are given below.

Flavoring System

Unnatural flavor - Caused by using flavours that are not typical of the designated flavour i.e. wintergreen flavour on vanilla ice cream. esp. vanillin

Egg: Caused by using too much egg in an ice cream that is not specified as a custard ice cream - resembles French vanilla ice cream .

Processing

Cooked: Caused by using milk products heated to too high a temperature or by using excessively high temperatures in mix pasteurization. It can dissipate with time, the same as cooked defect in fluid milk. Sulfhydryl flavor: Caramel-like, scalded milk, oatmeal-like.

Dairy Ingredients

High Acid: Use of dairy products with high acidity (usually due to bacterial spoilage) or holding mix too long and at too high a temperature before freezing. Acid/sour flavours are more rare these days due to the growth of proteolytic psychrotrophs during storage at elevated temperatures, rather than lactic acid bacteria.

Salty: Ice cream too high in milk solids-not-fat. Too much salt may have been added to the mix. High whey powder, or maybe salted butter used instead of sweet butter.
Old Ingredient: Caused by the use of inferior dairy products in the preparation of the mix. Powders made from poor milk or stored too long at elevated temperature or butter made from poor cream will contribute to old ingredient flavour. Unpleasant aftertaste.
Oxidized: Caused by oxidation of the fat or lipid material such as phospholipid, similar to fluid milk oxidation. Induced by the presence of copper or iron in the mix or from the milk itself. Mono-and-di-glyceride or Polysorbate 80 can also oxidize. Various stages - cardboardy, metallic (also described as painty, fishy).
Rancid: Caused by rancidity (high level of free butyric acid from lipolysis) of milk fat. May be due to use of rancid dairy products (pumping or excessive foaming of raw milk or cream) or to insufficient heat before homogenization of mix. See description of Lipolysis, especially the release of free butyric acid.

Others

Storage: Usually develops from "Lacks Freshness" and is most pronounced on ice cream which have been held in a stale storage atmosphere. Ice cream can also pick up absorbed volatile flavours from the storage environment (e.g., paint, ammonia, or in dipping cabinets - volatiles from nearby flavours.

Body and Texture Defects

1. Coarse/Icy Texture: Due to the presence of ice crystals of such a size that they are noticeable when the ice cream is eaten. See ice cream structure, the freezing aspects of ice cream manufacturing, ice cream freezing theory, and ice cream shelf life. May be caused by:

• Insufficient total solids (high water content).
• Insufficient protein.
• Insufficient stabilizer or poor stabilizer.
• Insufficient homogenizing pressure (due to its effect on fat structure formation).
• Insufficient aging of the mix (stabilizer hydration, also fat crystallization and development of resulting fat structure).
• Slow freezing because of mechanical condition of freezer.
• Incorporation of air as large cells because of physical characteristics of mix or type of freezer used.
• Slow hardening.
• Fluctuating storage room temperatures.
• Rehardening soft ice cream.
• Pumping ice cream too far from continuous freezer before hardening.
• Fluctuating temperatures during storage and distribution - the most likely cause! See discussion of ice cream shelf life.

2. Crumbly Body: A flaky or snowy characteristic caused by:

• High overrun together with large air cells.
• Low stabilizer or emulsifier.
• Low total solids.
• Low protein.

3. Fluffy Texture: A spongy/marshmallowy characteristic caused by:

• Incorporation of large amount of air.
• Low total solids.
• Low stabilizer content.

4. Gummy Body: This defect is the opposite of Crumbly in that it imparts a pasty or putty-like body. It is caused by:

• Too low an overrun.
• Too much stabilizer.
• Poor stabilizer.

5. Sandy Texture: One of the most objectionable texture defects but easiest to detect. It is caused by Lactose crystals, which do not dissolve readily and produce a rough or gritty sensation in the mouth. This can be distinguished from "iciness" because the lactose crystals do not melt in your mouth. This defect can be prevented by many of the same factors that inhibit iciness:

• hardening the ice cream quickly
• maintaining low storage room temps.
• preventing temperature fluctuations...from manufacturer to consumer

Lactose crystal formation is further discussed in the Dairy Chemistry and Physics section.

6. Weak Body: Ice cream lacks "chewiness" and melts quickly into a watery liquid. Gives impression of lacking richness. May be caused by:

• Low total solids.
• High overrun.
• Insufficient stabilizer.

Melting Quality Characteristics

1. Curdy Melt-Down: May be due to visible fat particles or due to coagulation of the milk proteins so is affected by factors that influence fat destabilization or the protein stability such as:

• High acidity (protein coagulation).
• Salt balance (protein coagulation).
• High homogenizing pressures (fat coagulation).
• Over-freezing in the freezer (fat coagulation).

2. Does not Melt: See ice cream structure, under the section on melt-down and fat structure/destabilization. May be caused by:

• Over emulsification.
• Wrong emulsifier.
• High fat.
• Excessive fat clumping in the mix due to homogenization at too low a temperature or single-stage homogenizer.
• Freezing to too low a temperature at freezer.

3. Wheying off: The salt balance, protein composition, and carrageenan addition (or lack or it) all are factors.

Colour Defects

1. Colour Uneven: Applies usually to ice cream in which colour has been used, but may be noticed in vanilla ice cream under some circumstances.

2. Colour Unnatural:

• Wrong shade of color used for flavoured ice cream.
• Too much yellow coloring used in vanilla ice cream.
• Grayish color due to neutralization.

Shrinkage

A very troublesome defect in ice cream since there appears to be no single cause or remedy. Defect shows up in hardened ice cream and manifests itself in reduced volume of ice cream in the container usually by pulling away from the top and/or sides of container. Structurally, it is caused by a loss of spherical air bubbles and formation of continuous air channels. Some factors believed associated with the defect are:

• Freezing and hardening at ultra low temperatures.
• Storage temperature. Both low and high appear to contribute.
• Excessive overruns.
• Pressure changes, for example, from altitude changes (lids popping when shipped to high altitudes, shrinkage when returned to low altitudes).

NOTE: Retailing: More so than other frozen products, ice cream requires constant, uninterrupted freezing cycle at low temperatures to avoid problems. Problems at retail level can arise from overfilling of display cabinet, heat from display lamps or door defrosters, hot air from incorrectly positioned circulation fans, displaying ice cream together with semi-frozen goods.

Finding Science in Ice Cream - An Experiment for Secondary School Classrooms

For further information about Finding Science in Ice Cream:
Professor Douglas Goff, Ph.D.
Department of Food Science
University of Guelph
Guelph, Ontario
N1G 2W1
tel: (519)824-4120 ext. 53878
fax: (519)824-6631
e-mail: dgoff@uoguelph.ca
This page was designed as a supplement to a classroom experiment for school teachers on ice cream making. Details of ice cream ingredients, manufacturing, structure, and many other aspects can be found on my main site at:
http://foodsci.uoguelph.ca/dairyedu/icecream.html
As the hot weather approaches and students minds begin to drift from the rigors of the school classroom or laboratory, a fun afternoon might be spent making ice cream and in so doing, introducing several aspects of the science and technology "behind the scenes". To suggest that there is no science in ice cream could not be further from the truth. I have made a career out of ice cream research which has taken me into aspects of physical and organic chemistry, microbiology, and chemical engineering to name but a few. Because all of you are from different disciplines and teach in different ways, I will give you enough background information and practice from which you can prepare your own experimental work. You can use the ice cream lab, for example, to demonstrate heat transfer in physics classes, freezing point depression phenomena and emulsions and foams in chemistry classes, or pasteurization and the food use of seaweeds(!) in biology classes. However you use the following information, even if it is for your own family picnic this summer, I hope you enjoy it!
The History of Ice Cream
Once upon a time, hundreds of years ago, Charles I of England hosted a sumptuous state banquet for many of his friends and family. The meal, consisting of many delicacies of the day, had been simply superb but the "coup de grace" was yet to come. After much preparation, the King's French chef had concocted an apparently new dish. It was cold and resembled fresh-fallen snow but was much creamier and sweeter than any other after-dinner dessert. The guests were delighted, as was Charles, who summoned the cook and asked him not to divulge the recipe for his frozen cream. The King wanted the delicacy to be served only at the Royal table and offered the cook 500 pounds a year to keep it that way. Sometime later, however, poor Charles fell into disfavour with his people and was beheaded in 1649. But by that time, the secret of the frozen cream remained a secret no more. The cook, named DeMirco, had not kept his promise.
This story is just one of many of the fascinating tales which surround the evolution of our country's most popular dessert, ice cream. It is likely that ice cream was not invented, but rather came to be over years of similar efforts. Indeed, the Roman Emperor Nero Claudius Caesar is said to have sent slaves to the mountains to bring snow and ice to cool and freeze the fruit drinks he was so fond of. Centuries later, the Italian Marco Polo returned from his famous journey to the Far East with a recipe for making water ices resembling modern day sherbets.
In 1774, a caterer named Phillip Lenzi announced in a New York newspaper that he had just arrived from London and would be offering for sale various confections, including ice cream. Dolly Madison, wife of U.S. President James Madison, served ice cream at her husband's Inaugural Ball in 1813. Commercial production was begun in North America in Baltimore, Maryland, 1851, by Mr. Jacob Fussell, now known as the father of the American ice cream industry. The first Canadian to start selling ice cream was Thomas Webb of Toronto, a confectioner, around 1850. William Neilson produced his first commercial batch of ice cream on Gladstone Ave. in Toronto in 1893, and his company produced ice cream at that location for close to 100 years. The ice cream division of Neilson was recently purchased by Ault Foods of London, Ont.

The Composition of and Ingredients in Ice Cream
Today's ice cream has the following composition : a) greater than 10% milkfat by legal definition, and usually between 10% and as high as 16% fat in some premium ice creams; b) between 9 and 12% milk solids-not-fat, the component which contains the proteins (caseins and whey proteins) and carbohydrates (lactose) found in milk; c) 12% to 16% sweeteners, usually a combination of sucrose and glucose-based corn syrup sweeteners; and d) 0.2% to 0.5% added stabilizers and emulsifiers, necessary components that unfortunately have unfamiliar sounding names that occupy three-quarters of the space of the ingredient listing and that will be described subsequently. The balance, usually 55% to 64%, is water, which comes from the milk. Ice milk is very similar to the composition of ice cream but contains between 3% and 5% milkfat by definition. Light ice cream contains between 8% and 10% milkfat.
The ingredients used to supply this composition include: a) a concentrated source of the milkfat, usually cream or butter; b) a concentrated source of the milk solids-not-fat component, usually evaporated milk or milk powder; c) sugars including sucrose and "glucose solids", a product derived from the partial hydrolysis of the corn starch component in corn syrup; and d) milk.
The fat component adds richness of flavour, contributes to a smooth texture with creamy body and good meltdown, and adds lubrication to the palate as it is consumed. The milk solids-not-fat component also contributes to the flavour but more importantly improves the body and texture of the ice cream by offering some "chew resistance" and enhancing the ability of the ice cream to hold its air. The sugars give the product its characteristic sweetness and palatability and enhance the perception of various fruit flavours. In addition, the sugars, including the lactose from the milk components, contribute to a depressed freezing point so that the ice cream has some unfrozen water associated with it at very low temperatures typical of their serving temperatures, -15^o to -18^oC. Without this unfrozen water, the ice cream would be too hard to scoop.
Freezing point depression of a solution is a colligative property associated with the number of dissolved molecules. The lower the molecular weight, the greater the ability of a molecule to depress the freezing point. Thus monosaccharides such as fructose or glucose produce a much softer ice cream than disaccharides such as sucrose. This limits the amount and type of sugar which one can successfully incorporate into the formulation.
The stabilizers are a group of compounds, usually polysaccharides, that are responsible for adding viscosity to the unfrozen portion of the water and thus holding this water so that it cannot migrate within the product. This results in an ice cream that is firmer to the chew. Without the stabilizers, the ice cream would become coarse and icy very quickly due to the migration of this free water and the growth of existing ice crystals. The smaller the ice crystals in the ice cream, the less detectable they are to the tongue. Especially in the distribution channels of today's marketplace, the supermarkets, the trunks of cars, and so on, ice cream has many opportunities to warm up, partially melt some of the ice, and then refreeze as the temperature is once again lowered. This process is known as heat shock and every time it happens, the ice cream becomes more icy tasting. Stabilizers help to prevent this.
Gelatin, a protein of animal origin, was used almost exclusively in the ice cream industry as a stabilizer but has gradually been replaced with polysaccharides of plant origin due to their increased effectiveness and reduced cost. The stabilizers in use today include: a) carboxymethyl cellulose, derived from the bulky components of plant material; b) locust bean gum which is derived from the beans of exotic trees grown mostly in Africa (Note: locust bean gum is a synonym for carob bean gum, the beans of which were used centuries ago for weighing precious metals, a system still in use today, the word carob and Karat having similar derivation) ; c) guar gum, from the guar bush, a member of the legume family grown in India for centuries and now grown to a limited extent in Texas; d) carrageenan, an extract of Irish Moss or red algae, originally harvested from the coast of Ireland; or e) sodium alginate, an extract of another seaweed, brown kelp. Often, two or more of these stabilizers are used in combination to lend synergistic properties to each other and improve their overall effectiveness.
The emulsifiers are a group of compounds in ice cream which aid in developing the appropriate fat structure and air distribution necessary for the smooth eating and good meltdown characteristics desired in ice cream. Emulsifiers are characterized by having a molecular structure which allows part of the molecule to be readily solubilized in a polar compound such as water, and another part of the molecule to be more readily solubilized in non-polar solvents such as fats. As a result, emulsifiers reside at the interface between fat and water, and lower the free energy or tension associated with two immiscible liquids in contact with each other. Their action will be more fully explained in the section below on emulsions and foams.
The original ice cream emulsifier was egg yolk, which was used in most of the original recipes. Today, two emulsifiers predominate most ice cream formulations: a) mono- and di-glycerides , derived from the partial hydrolysis of fats or oils of animal or vegetable origin; and b) Polysorbate 80, a product consisting of a glucose molecule bound to a fatty acid, oleic acid. Both of these compounds have hydrophobic regions ( the "fat loving" part), the fatty acids, and hydrophilic regions ( the "water loving" part), either glycerol or glucose. All of the compounds mentioned above are either fats or carbohydrates, important components in most of the foods we eat and need.
Together, the stabilizers and emulsifiers make up less than one half percent by weight of our ice cream. They are all compounds that have been exhaustively tested for safety and have received the "generally recognized as safe" or GRAS status.
The Manufacturing Process
Ingredients are chosen by the manufacturer on the basis of desired quality, availability, and cost. The ingredients are blended together and produce what is known as the "ice cream mix". The mix is first pasteurized. Pasteurization is a process which is designed to kill all of the possible pathogens (disease causing organisms) that may be present. Organisms such as Mycobacterium tuberculosis, Salmonella, Staphylococcus, Listeria, and others that cause human disease can be found associated with farm animals and thus raw milk products must be pasteurized. In addition to this very important function, pasteurization also reduces the number of spoilage organisms such as psychrotrophs, and helps to "cook" the mix. The mix is also homogenized which forms the fat emulsion by breaking down or reducing the size of the fat globules found in milk or cream to less than 1 µm. Homogenization helps to produce a smooth product when frozen. The mix is then aged for at least four hours and usually overnight. This allows time for the fat to cool down and crystallize, and for the proteins and polysaccharides to fully hydrate.
Following mix processing, the mix is drawn into a flavour tank where any liquid flavours, fruit purees, or colours are added. The mix then enters the dynamic freezing process which both freezes a portion of the water and whips air into the frozen mix. The "barrel" freezer is a scraped-surface, tubular heat exchanger, which is jacketed with a boiling refrigerant such as ammonia or freon. Mix is pumped through this freezer and is drawn off the other end in a matter of 30 seconds, (or 10 to 15 minutes in the case of batch freezers) with about 50% of its water frozen. There are rotating blades inside the barrel that keep the ice scraped off the surface of the freezer and also dashers inside the machine which help to whip the mix and incorporate air. Ice cream contains a considerable quantity of air, up to half of its volume. This gives the product its characteristic lightness. Without air, ice cream would be similar to a frozen ice cube.
As the ice cream is drawn with about half of its water frozen, particulate matter such as fruits, nuts, candy, cookies, or whatever you like, is added to the semi-frozen slurry which has a consistency similar to soft-serve ice cream. In fact, almost the only thing which differentiates hard frozen ice cream from soft-serve, is the fact that soft serve is drawn into cones at this point in the process rather than into packages for subsequent hardening. After the particulates have been added, the ice cream is packaged and is placed into a blast freezer at -30^o to -40^oC where most of the remainder of the water is frozen. Below about -25^oC, ice cream is stable for indefinite periods without danger of ice crystal growth; however, above this temperature, ice crystal growth is possible and the rate of crystal growth is dependant upon the temperature of storage. This limits the shelf life of the ice cream.
Salt and ice
Making ice cream at home requires the use of an ice cream machine. The "homemade" or hand-crank freezer used was the forerunner to today's modern equipment. Many people enjoy fond memories of hot summer days spent preparing the ice cream mix, loading the bucket with ice and salt, and cranking the freezer for a half hour until it was considered too stiff to continue or until one's hunger got the best of them. All of the various steps in making ice cream via the bucket are similar to the commercial processing stages. The mix is prepared and pasteurized, aged, dynamically whipped and frozen in a freezer equipped with blades and dashers, and then hardened prior to consumption. Ice and salt are used, however, rather than the ammonia or Freon jacket in the commercial freezer above.
The concept of melting ice with salt is not new to anyone in this latitude. Indeed, our roads, driveways, and sidewalks are kept bare in the winter by such a process. As salt is applied to ice, a concentrated brine solution forms on the ice, which has a very low freezing point. The freezing point of a 20% solution of salt is -16.6^oC. As a result, more ice melts to dilute this solution, until the freezing point of the solution matches the outside temperature (equilibrium is established). The same phenomenon is occurring in the brine solution in the ice cream freezer. As the salt continues to dissolve more ice melts to accommodate this concentrated salt solution with its very low melting point. At the same time, both the heat of solution of the dissolving salt, and the latent heat of fusion of the melting ice are adsorbed from the ice itself, thereby lowering the temperature of the salt, ice and brine mixture. The temperature of this mixture can be controlled by the amount and ratio of salt and ice present. As examples, consider the following data: a 2% NaCl (salt) solution has a freezing point of -1.4^oC, 5% salt conc. = -3.5^oC, 10% salt = -7.4^oC, 15% salt = -11.7^oC and 20% salt = -16.6^oC. The lowest temperature which can be achieved with a sodium chloride brine is -20^oC, at a concentration of 23% salt. Higher concentrations result in salt crystallization.
This brine, in turn, is adsorbing heat from the freezing ice cream inside the can, and thus ice and salt need to be continually added to keep the ice temperature low enough to freeze the ice cream. (Bear in mind that the freezing temperature of the ice cream is depressed below 0o due to the presence of dissolved sugars.) This process is a lesson in heat transfer in itself!

The Structure of Ice Cream - Emulsions and Foams
An emulsion is defined as liquid droplets dispersed in another immiscible liquid. The dispersed phase droplet size ranges from 0.1-10 µm. Important oil-in-water food emulsions, ones in which oil or fat is the dispersed phase and water is the continuous phase, include milk, cream, ice cream, salad dressings, cake batters, flavour emulsions, meat emulsions, and cream liqueurs. Examples of food water-in-oil emulsions are butter or margarine. Emulsions are inherently unstable because free energy is associated with the interface between the two phases. As the interfacial area increases, either through a decrease in particle size or the addition of more dispersed phase material, i.e. higher fat, more energy is needed to keep the emulsion from coalescing. Some molecules act as surface active agents (called surfactants or emulsifiers) and can reduce this energy needed to keep these phases apart.
A foam is defined as a gas dispersed in a liquid where the gas bubbles are the discrete phase. There are many food foams including whipped creams, ice cream, carbonated soft drinks, mousses, meringues, and the head of a beer. A foam is likewise unstable and needs a stabilizing agent to form the gas bubble membrane.
Ice cream is both an emulsion and a foam. The milkfat exists in tiny globules that have been formed by the homogenizer. There are many proteins which act as emulsifiers and give the fat emulsion its needed stability. The emulsifiers discussed above in the Ingredients section which are added to ice cream actually reduce the stability of this fat emulsion because they replace proteins on the fat surface. When the mix is subjected to the whipping action of the barrel freezer, the fat emulsion begins to partially break down and the fat globules begin to flocculate. The air bubbles which are being beaten into the mix are stabilized by this partially coalesced fat. If emulsifiers were not added, the fat globules would have so much ability to resist this coalescing due to the proteins being adsorbed to the fat globule that the air bubbles would not be properly stabilized and the ice cream would not have the same smooth texture (due to this fat structure) that it has.
This fat structure which exists in ice cream is the same type of structure which exists in whipped cream. When you whip a bowl of heavy cream, it soon starts to become stiff and dry appearing and takes on a smooth texture. This results from the formation of this partially coalesced fat structure stabilizing the air bubbles. If it is whipped too far, the fat will begin to churn and butter particles will form. The same thing will happen in ice cream which has been whipped too much.
Also adding structure to the ice cream is the formation of the ice crystals. Water freezes out of a solution in its pure form as ice. In a sugar solution such as ice cream, the initial freezing point of the solution is lower than 0^oC due to these dissolved sugars. As ice crystallization begins and water freezes out in its pure form, the concentration of the remaining solution of sugar is increased due to water removal and hence the freezing point is further lowered. This process, known as freeze concentration, continues to very low temperatures. Even at the typical ice cream serving temperature of -16^oC, only about 72% of the water is frozen. The rest remains as a very concentrated sugar solution. This helps to give ice cream its ability to be scooped and chewed at freezer temperatures. The air content also contributes to this ability as mentioned above in discussing freezing.
Thus the structure of ice cream can be described as a partly frozen foam with ice crystals and air bubbles occupying a majority of the space. The tiny fat globules, some of them flocculated and surrounding the air bubbles also form a dispersed phase. Proteins and emulsifiers are in turn surrounding the fat globules. The continuous phase consists of a very concentrated, unfrozen solution of sugars.
One gram of ice cream of typical composition contains 1.5 x 10e12 fat globules of average diameter 1 µm that have a surface area of greater than 1 square meter (in a gram!), 8 x 10e6 air bubbles of average diameter 70 µm with a surface area of 0.1 sq. m., and 8 x 10e6 ice crystals of average diameter 50 µm with a surface area of another 0.1 sq. m. The importance of surface chemistry becomes obvious!

The Logistics of the Experiment
Depending on the available resources, an old-fashioned hand-crank or electric type freezer can be used. Please see my Homemade Ice Cream page for directions.
However, there are alternatives. Here is directions from a clever experiment I received from a science enrichment Grade 1-4 teacher:
each student places in a small zip loc baggy (the heavy-duty, freezer type) - 1 T sugar, 1/2 t vanilla, 1/2 cup milk. Secure zip loc and place small baggy in a larger zip loc baggy (also the heavy duty kind). Surround the small baggy with ice to 1/2 large baggy full and put in 6 T salt on ice. Next, shake the baggies 5-10 minutes and the students have made their own serving of ice cream. Chocolate syrup on top is really good.
An alternative is to use liquid nitrogen for the freezing. Use a mix of standard recipe (see homemade ice cream page). Place the mix on a very large stainless steel bowl, about 1/3 full, and have a student stir the mix very quickly with a wire whisk (very quickly!). Have someone else pour a small quantity of liquid nitrogen into the mix while being stirred (stir as long and as fast as you possibly can). It will freeze instantly. Let the ice cream sit for a few minutes to ensure there is no liquid nitrogen left, and then eat when it is at the right consistency. A few words of caution - this experiment is pretty safe for older children (I have done it many times in high school classes), but liquid nitrogen needs to be handled cautiously. Wear gloves, don't spill on skin, etc.

I hope you have enjoyed this overview of ice cream processing and chemistry and have gained some useful insights into the field of Food Science, and that from this overview you might be able to have some fun with your students and pass along to them some of our enthusiasm for this field. In today's world of rapidly expanding technology, evident even on the grocery store shelf, we need students who are willing to learn and apply new and existing technologies to the stable, exciting, vital, and profitable food industry.

Professor Doug Goff
Dept. of Food Science
University of Guelph

Ice Cream - Manufacturing Technique

 

The first step in the manufacture of ice cream involves selection of ingredients

The items may be classified as dairy and non-dairy ingredients. The dairy items include sweet cream, frozen cream, plastic cream, unsalted butter, butteroil, whole milk, whole milk powder, condensed whole milk and evaporated milk.
The non-dairy items include sugar (cane sugar, beet sugar and corn sugar), stabilizers (gelatin or sodium alginate), emulsifiers (glycerol monostearate), flavours (vanilla, chocolate, strawberry, pineapple, lemon, banana etc), colours (yellow, green, pink depending on the flavours), egg solids, fruits and nuts (apple, banana, mango, grape, almond, pistachio, cashew, walnut etc.).
The second step is figuring the mix. Although knowledge of calculation is required for manufacturing ice cream with quality that adheres to the legal standards, it is indeed easy to figure the mix by simple methods.For E.g. To make 1 litre ice cream mix that meets the legal requirements, the following ingredients are required.

Whole milk	1 litre
Skim milk powder	70 g
Butter	100 g
Cane sugar	220 g
Gelatin	8 g
Glycerol monostearate	6 g
Vanilla concentrate	Q.S

Making the mix

Care should be exercised while selecting the dairy as well as non dairy ingredients as they determine the quality of the ultimate end product i.e. ice cream. Take the milk in a container and allow it to be heated. When the temperature of milk is around 50°C, solid ingredients like skim milk powder, butter (cut in to small pieces) and sugar are added slowly so as to completely incorporate them in the hot milk. Gelatin and glycerol monosterate (GMS) are preferably mixed together and heated separately in minimum quantity of water till their dissolution and added in to the hot milk. The pasteurization of ice cream mix involves heating it to 68.5°C for 30 min or 80°C for 25 sec.
Homogenization of ice cream mix is an essential step in the manufacturing process. It is usually done at temperatures from 63-77°C in a two stage homogenizer; the first stage operating at 2500 psi and the second one at 500 psi. Homogenization helps in reducing the size of the fat globules to 2 microns or less. It helps in preventing the fat separation during ageing, imparts smoother texture to product, improves whipping ability, reduces ageing period and reduces the quantity of stabilizer required.

Cooling and ageing of the ice cream mix

Ice cream mix is cooled to 0-5°C immediately after homogenization and it is held at this temperature for 3 to 4 hours in the ageing tanks. Ageing of the ice cream mix is not required when sodium alginate is used as a stabilizer. Ageing improves the body and texture of the ice cream, increases melting resistance and improves maximum over run.

Freezing the mix

After completing the ageing process, the ice cream mix is subjected to freezing in a batch freezer or continuous ice cream freezer.
Generally colours and flavours are added to the aged ice cream mix just before transferring the same in to the freezer or they can be added directly in to the freezer. In the freezing chamber, the ice cream mix is quickly frozen while being continuously agitated to incorporate air in a manner to produce and control the formation of large number of small ice crystals which will provide smooth body and texture, palatability and desired over run in the finished end product. When the ice cream is frozen to the required consistency, it is transferred to the packages of desired sizes and immediately placed in cold storage rooms.
During the cold storage process, freezing and hardening is completed. The temperature of hardening is around -20°C. The softy ice cream is usually drawn from the freezer at around -7°C. Nature of freezing is very important in freezing process. It is always desirable to freeze the mix in a continuous freezer rather than in batch freezer as the former accomplishes the task within a few seconds whereas the latter does it in 5-10 min.

Overrun in ice cream

Overrun, expressed as percentage, is generally defined as the volume of ice cream obtained in excess of the volume of the ice cream mix. The excess volume is composed mainly of the air incorporated during the freezing process. The over run due to air provides proper body, texture and palatability essential to a good quality product. Too much and too little quantity of air incorporation will affect the body, texture and palatability. The softy ice cream, ice cream packaged in bulk and retail packed ice cream will have over run of 30-50%, 90-100% and 70-80% respectively.

Uses of ice cream

Ice cream is liked by all age group of people and it is directly consumed as a frozen dessert. Ice cream can also be used as a topping for fruit salads and fruit pies.

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Ice cream

From Wikipedia, the free encyclopedia

For other uses, see Ice cream (disambiguation).

Ice cream or gelato in Rome, Italy
Origin
Alternative name(s)	Gelato, sorbet, frozen custard
Details
Course	Dessert
Main ingredient(s)	Milk/cream, sugar
Variations	Strawberry, chocolate, vanilla, etc.

Ice cream (formerly and properly ice-cream, derived from earlier iced cream or cream ice^[1]) is a frozen dessert usually made from dairy products, such as milk and cream, and often combined with fruits or other ingredients and flavours. Most varieties contain sugar, although some are made with other sweeteners. In some cases, artificial flavourings and colourings are used in addition to, or instead of, the natural ingredients. The mixture of chosen ingredients is stirred slowly while cooling, in order to incorporate air and to prevent large ice crystals from forming. The result is a smoothly textured semi-solid foam that is malleable and can be scooped.
The meaning of the term "ice cream" varies from one country to another. Terms such as "frozen custard", "frozen yogurt", "sorbet", "gelato" and others are used to distinguish different varieties and styles. In some countries, such as the USA, the term "ice cream" applies only to a specific variety, and most governments regulate the commercial use of the various terms according to the relative quantities of the main ingredients.^[2] In other countries, such as Italy and Argentina, one word is used for all variants. Analogues made from dairy alternatives, such as goat's or sheep's milk, or milk substitutes, are available for those who are lactose intolerant, allergic to dairy protein, and/or vegan. Popular flavours of ice cream include vanilla, chocolate, coffee, strawberry, raspberry ripple, neapolitan and tutti frutti. It should be pointed out that vanilla ice cream is very frequently not made with true vanilla, but with vanilla flavouring; as vanilla is the second most expensive spice in the world after saffron, this helps to keep the market value of vanilla ice cream down.

Contents  [hide]  1 History 1.1 Precursors of ice cream 1.2 True ice cream 2 Production 3 Commercial delivery 4 Dietary 5 Ice cream around the world 6 Ice cream cone 7 Other frozen desserts 8 Cryogenic 9 See also 10 References 11 External links

History

Precursors of ice cream

An ice cream store in Damascus, Syria

In the Persian Empire, people would pour grape-juice concentrate over snow, in a bowl, and eat this as a treat, especially when the weather was hot. Snow would either be saved in the cool-keeping underground chambers known as "yakhchal", or taken from snowfall that remained at the top of mountains by the summer capital - Hagmatana, Ecbatana or Hamedan of today. In 400 BC, the Persians went further and invented a special chilled food, made of rose water and vermicelli, which was served to royalty during summers.^[3] The ice was mixed with saffron, fruits, and various other flavours.
Ancient civilizations have served ice for cold foods for thousands of years. The BBC reports that a frozen mixture of milk and rice was used in China around 200 BC.^[4] The Roman Emperor Nero (37–68) had ice brought from the mountains and combined it with fruit toppings. These were some early chilled delicacies.^[5]
Arabs were perhaps the first to use milk as a major ingredient in the production of ice cream. They sweetened it with sugar rather than fruit juices, and perfected means of commercial production. As early as the 10th century, ice cream was widespread among many of the Arab world's major cities, such as Baghdad, Damascus, and Cairo. It was produced from milk or cream, often with some yoghurt, and was flavoured with rosewater, dried fruits and nuts. It is believed that the recipe was based on older Ancient Arabian, Mesopotamian, Greek, or Roman recipes, which were, it is presumed, the first and precursors to Persian faloodeh.
Maguelonne Toussaint-Samat asserts, in her History of Food, that "the Chinese may be credited with inventing a device to make sorbets and ice cream. They poured a mixture of snow and saltpetre over the exteriors of containers filled with syrup, for, in the same way as salt raises the boiling-point of water, it lowers the freezing-point to below zero."^[6][7] (Toussaint does not provide historical documentation for this.) Some distorted accounts claim that in the age of Emperor Yingzong, Song Dynasty (960-1279) of China, a poem named "詠冰酪" (Ode to the ice cheese) was written by the poet Yang Wanli. Actually, this poem was named "詠酥” (Ode to the pastry; 酥 is a kind of food much like pastry in the Western world) and has nothing to do with ice cream.^[8] It has also been claimed that, in the Yuan Dynasty, Kublai Khan enjoyed ice cream and kept it a royal secret until Marco Polo visited China and took the technique of making ice cream to Italy.

Japanese green tea ice cream with anko sauce

In the sixteenth century, the Mughal emperors used relays of horsemen to bring ice from the Hindu Kush to Delhi, where it was used in fruit sorbets.^[9]
When Italian duchess Catherine de' Medici married the duc d’Orléans in 1533, she is said to have brought with her to France some Italian chefs who had recipes for flavoured ices or sorbets.^[10] One hundred years later, Charles I of England was, it was reported, so impressed by the "frozen snow" that he offered his own ice cream maker a lifetime pension in return for keeping the formula secret, so that ice cream could be a royal prerogative.^[11] There is no historical evidence to support these legends, which first appeared during the 19th century.
The first recipe in French for flavoured ices appears in 1674, in Nicholas Lemery’s Recueil de curiositéz rares et nouvelles de plus admirables effets de la nature.^[10] Recipes for sorbetti saw publication in the 1694 edition of Antonio Latini's Lo Scalco alla Moderna (The Modern Steward).^[10] Recipes for flavoured ices begin to appear in François Massialot's Nouvelle Instruction pour les Confitures, les Liqueurs, et les Fruits, starting with the 1692 edition. Massialot's recipes result in a coarse, pebbly texture. Latini claims that the results of his recipes should have the fine consistency of sugar and snow.^[10]

True ice cream

Ice cream recipes first appeared in 18th-century England and America. The recipe for ice cream was published in Mrs. Mary Eales's Receipts in London in 1718.^[12][13]
To ice cream.
Take Tin Ice-Pots, fill them with any Sort of Cream you like, either plain or sweeten’d, or Fruit in it; shut your Pots very close; to six Pots you must allow eighteen or twenty Pound of Ice, breaking the Ice very small; there will be some great Pieces, which lay at the Bottom and Top: You must have a Pail, and lay some Straw at the Bottom; then lay in your Ice, and put in amongst it a Pound of Bay-Salt; set in your Pots of Cream, and 93 lay Ice and Salt between every Pot, that they may not touch; but the Ice must lie round them on every Side; lay a good deal of Ice on the Top, cover the Pail with Straw, set it in a Cellar where no Sun or Light comes, it will be froze in four Hours, but it may stand longer; then take it out just as you use it; hold it in your Hand and it will slip out. When you wou’d freeze any Sort of Fruit, either Cherries, Rasberries, Currants, or Strawberries, fill your Tin-Pots with the Fruit, but as hollow as you can; put to them Lemmonade, made with Spring-Water and Lemmon-Juice sweeten’d; put enough in the Pots to make the Fruit hang together, and put them in Ice as you do Cream.
The earliest reference to ice cream given by the Oxford English Dictionary is from 1744, reprinted in a magazine in 1877. 1744 in Pennsylvania Mag. Hist. & Biogr. (1877) I. 126 Among the rarities..was some fine ice cream, which, with the strawberries and milk, eat most deliciously.^[14]
The 1751 edition of The Art of Cookery made Plain and Easy by Hannah Glasse features a recipe for ice cream. OED gives her recipe: H. GLASSE Art of Cookery (ed. 4) 333 (heading) To make Ice Cream..set it [sc. the cream] into the larger Bason. Fill it with Ice, and a Handful of Salt.^[14]
The year 1768 saw the publication of L'Art de Bien Faire les Glaces d'Office by M. Emy, a cookbook devoted entirely to recipes for flavoured ices and ice cream.^[10]
Ice cream was introduced to the United States by Quaker colonists who brought their ice cream recipes with them. Confectioners sold ice cream at their shops in New York and other cities during the colonial era. Ben Franklin, George Washington, and Thomas Jefferson were known to have regularly eaten and served ice cream. First Lady Dolley Madison is also closely associated with the early history of ice cream in the United States. One respected history of ice cream states that, as the wife of U.S. President James Madison, she served ice cream at her husband's Inaugural Ball in 1813.
Around 1832, Augustus Jackson, an African American confectioner, not only created multiple ice cream recipes but also invented a superior technique to manufacture ice cream.^[15]
In 1843, Nancy Johnson of Philadelphia was issued the first U.S. patent for a small-scale handcranked ice cream freezer. The invention of the ice cream soda gave Americans a new treat, adding to ice cream's popularity. The invention of this cold treat is attributed to Robert Green in 1874, although there is no conclusive evidence to prove his claim.

Ice cream sundaes with fruit, nuts, and a wafer

The ice cream sundae originated in the late 19th century. Several men claimed to have created the first sundae, but there is no conclusive evidence to back up any of their stories. Some sources say that the sundae was invented to circumvent blue laws, which forbade serving sodas on Sunday. Towns claiming to be the birthplace of the sundae include Buffalo, New York; Two Rivers, Wisconsin; Ithaca, New York; and Evanston, Illinois. Both the ice cream cone and banana split became popular in the early 20th century. Several food vendors claimed to have invented the ice cream cone at the 1904 World's Fair in St. Louis, MO.^[16] Europeans were eating cones long before 1904.^[17][18]
In the UK, ice cream remained an expensive and rare treat, until large quantities of ice began to be imported from Norway and the US in the mid-Victorian era. A Swiss-Italian businessman, Carlo Gatti, opened the first ice cream stall outside Charing Cross station in 1851, selling scoops of ice cream in shells for one penny.^[19]

George and Davis' Ice Cream Cafe on Little Clarendon Street, Oxford.

The history of ice cream in the 20th century is one of great change and increases in availability and popularity. In the United States in the early 20th century, the ice cream soda was a popular treat at the soda shop, the soda fountain, and the ice cream parlor. During American Prohibition, the soda fountain to some extent replaced the outlawed alcohol establishments such as bars and saloons .
Ice cream became popular throughout the world in the second half of the 20th century after cheap refrigeration became common. There was an explosion of ice cream stores and of flavours and types. Vendors often competed on the basis of variety. Howard Johnson's restaurants advertised "a world of 28 flavors." Baskin-Robbins made its 31 flavours ("one for every day of the month") the cornerstone of its marketing strategy. The company now boasts that it has developed over 1000 varieties.
One important development in the 20th century was the introduction of soft ice cream. A chemical research team in Britain (of which a young Margaret Thatcher was a member)^[20][21] discovered a method of doubling the amount of air in ice cream, which allowed manufacturers to use less of the actual ingredients, thereby reducing costs. It made possible the soft ice cream machine in which a cone is filled beneath a spigot on order. In the United States, Dairy Queen, Carvel, and Tastee-Freez pioneered in establishing chains of soft-serve ice cream outlets.
Technological innovations such as these have introduced various food additives into ice cream, the notable one being the stabilizing agent gluten,^[22] to which some people have an intolerance. Recent awareness of this issue has prompted a number of manufacturers to start producing gluten-free ice cream.^[23]
The 1980s saw a return of the older, thicker ice creams being sold as "premium" and "superpremium" varieties under brands such as Ben & Jerry's and Häagen-Dazs.

Production

Cherry ice cream

Before the development of modern refrigeration, ice cream was a luxury reserved for special occasions. Making it was quite laborious; ice was cut from lakes and ponds during the winter and stored in holes in the ground, or in wood-frame or brick ice houses, insulated by straw. Many farmers and plantation owners, including U.S. Presidents George Washington and Thomas Jefferson, cut and stored ice in the winter for use in the summer. Frederic Tudor of Boston turned ice harvesting and shipping into a big business, cutting ice in New England and shipping it around the world.
Ice cream was made by hand in a large bowl placed inside a tub filled with ice and salt. This was called the pot-freezer method. French confectioners refined the pot-freezer method, making ice cream in a sorbetière (a covered pail with a handle attached to the lid). In the pot-freezer method, the temperature of the ingredients is reduced by the mixture of crushed ice and salt. The salt water is cooled by the ice, and the action of the salt on the ice causes it to (partially) melt, absorbing latent heat and bringing the mixture below the freezing point of pure water. The immersed container can also make better thermal contact with the salty water and ice mixture than it could with ice alone.
The hand-cranked churn, which also uses ice and salt for cooling, replaced the pot-freezer method. The exact origin of the hand-cranked freezer is unknown, but the first U.S. patent for one was #3254 issued to Nancy Johnson on September 9, 1843. The hand-cranked churn produced smoother ice cream than the pot freezer and did it quicker. Many inventors patented improvements on Johnson's design.
In Europe and early America, ice cream was made and sold by small businesses, mostly confectioners and caterers. Jacob Fussell of Baltimore, Maryland was the first to manufacture ice cream on a large scale. Fussell bought fresh dairy products from farmers in York County, Pennsylvania, and sold them in Baltimore. An unstable demand for his dairy products often left him with a surplus of cream, which he made into ice cream. He built his first ice cream factory in Seven Valleys, Pennsylvania, in 1851. Two years later, he moved his factory to Baltimore. Later, he opened factories in several other cities and taught the business to others, who operated their own plants. Mass production reduced the cost of ice cream and added to its popularity.
The development of industrial refrigeration by German engineer Carl von Linde during the 1870s eliminated the need to cut and store natural ice, and, when the continuous-process freezer was perfected in 1926, commercial mass production of ice cream and the birth of the modern ice cream industry was underway.
The most common method for producing ice cream at home is to use an ice cream maker, in modern times, in general, an electrical device that churns the ice cream mixture while cooled inside a household freezer, or using a solution of pre-frozen salt and water, which gradually melts while the ice cream freezes. Some more expensive models have an inbuilt freezing element. A newer method of making home-made ice cream is to add liquid nitrogen to the mixture while stirring it using a spoon or spatula. Some ice cream recipes call for making a custard, folding in whipped cream, and immediately freezing the mixture.

Commercial delivery

A bicycle-based ice cream vendor in Indonesia

Ice cream can be mass-produced and thus is widely available in developed parts of the world. Ice cream can be purchased in large cartons (vats and squrounds) from supermarkets and grocery stores, in smaller quantities from ice cream shops, convenience stores, and milk bars, and in individual servings from small carts or vans at public events. In Turkey and Australia, ice cream is sometimes sold to beach-goers from small powerboats equipped with chest freezers. Some ice cream distributors sell ice cream products from traveling refrigerated vans or carts (commonly referred to in the US as "ice cream trucks"), sometimes equipped with speakers playing children's music. Ice cream vans in the United Kingdom make a music box noise rather than actual music.

Dietary

The examples and perspective in this article deal primarily with the United States and do not represent a worldwide view of the subject. Please improve this article and discuss the issue on the talk page. (November 2011)

Black sesame soft ice cream, Japan

In the USA, ice cream may have the following composition:^[24]

• greater than 10% milkfat and usually between 10% and as high as 16% fat in some premium ice creams
• 9 to 12% milk solids-not-fat: this component, also known as the serum solids, contains the proteins (caseins and whey proteins) and carbohydrates (lactose) found in milk
• 12 to 16% sweeteners: usually a combination of sucrose and glucose-based corn syrup sweeteners
• 0.2 to 0.5% stabilisers and emulsifiers
• 55% to 64% water, which comes from the milk or other ingredients.

These compositions are percentage by weight. Since ice cream can contain as much as half air by volume, these numbers may be reduced by as much as half if cited by volume. In terms of dietary considerations, the percentages by weight are more relevant. Even the low-fat products have high caloric content: Ben and Jerry's No-Fat Vanilla Fudge contains 150 calories (630 kJ) per half-cup due to its high sugar content.^[25]

Ice cream around the world

Main article: Ice cream around the world

Ice cream cone

Main article: Ice cream cone

Mrs Marshall's Cookery Book, published in 1888, endorsed serving ice cream in cones,^[26] but the idea definitely predated that. Agnes Marshall was a celebrated cookery writer of her day and helped to popularise ice cream. She patented and manufactured an ice cream maker and was the first person to suggest using liquefied gases to freeze ice cream after seeing a demonstration at the Royal Institution.
Reliable evidence proves that ice cream cones were served in the 19th century, and their popularity increased greatly during the St. Louis World's Fair in 1904. According to legend, at the World's Fair an ice cream seller had run out of the cardboard dishes used to put ice cream scoops in, so they could not sell any more produce. Next door to the ice cream booth was a Syrian waffle booth, unsuccessful due to intense heat; the waffle maker offered to make cones by rolling up his waffles and the new product sold well, and was widely copied by other vendors.^[27][28]

Other frozen desserts

The following is a partial list of ice cream-like frozen desserts and snacks:

Raspberry sorbet.

• Ais kacang: a dessert in Malaysia and Singapore made from shaved ice, syrup, and boiled red bean and topped with evaporated milk. Sometimes, other small ingredients like raspberries and durians are added in, too.
• Dondurma: Turkish ice cream, made of salep and mastic resin
• Frozen custard: at least 10% milk fat and at least 1.4% egg yolk and much less air beaten into it, similar to Gelato, fairly rare. Known in Italy as Semifreddo.
• Frozen yogurt: a low-fat or fat-free alternative made with yogurt
• Gelato: an Italian frozen dessert having a lower milk fat content than ice cream.
• Halo-halo: a popular Filipino dessert that is a mixture of shaved ice and milk to which are added various boiled sweet beans and fruits, and served cold in a tall glass or bowl.
• Ice milk: less than 10% milk fat and lower sweetening content, once marketed as "ice milk" but now sold as low-fat ice cream in the United States.
• Popsicle (ice pop or ice lolly): frozen fruit puree, fruit juice, or flavoured sugar water on a stick or in a flexible plastic sleeve.
• Kulfi: Believed to have been introduced to South Asia by the Mughal conquest in the 16th century; its origins trace back to the cold snacks and desserts of Arab and Mediterranean cultures.^[29]
• Mellorine: non-dairy, with vegetable fat substituted for milk fat
• Parevine: Kosher non-dairy frozen dessert established in 1969 in New York^[30]
• Sherbet: 1–2% milk fat and sweeter than ice cream.
• Sorbet: fruit puree with no dairy products
• Snow cones, made from balls of crushed ice topped with sweet syrup served in a paper cone, are consumed in many parts of the world. The most common places to find snow cones in the United States are at amusement parks.
• Maple toffee: A popular springtime treat in maple-growing areas is maple toffee, where maple syrup boiled to a concentrated state is poured over fresh snow congealing in a toffee-like mass, and then eaten from a wooden stick used to pick it up from the snow.

Cryogenic

Dippin' Dots Flavored Ice Cream

Using liquid nitrogen to freeze ice cream is an old idea and has been used for many years to harden ice cream. The use of liquid nitrogen in the primary freezing of ice cream, that is to effect the transition from the liquid to the frozen state without the use of a conventional ice cream freezer, has only recently started to see commercialization. Some commercial innovations have been documented in the National Cryogenic Society Magazine "Cold Facts".^[31] The most noted brands are Dippin' Dots,^[32] Blue Sky Creamery,^[33] Project Creamery,^[34] and Sub Zero Cryo Creamery.^[35] The preparation results in a column of white condensed water vapor cloud, reminiscent of popular depictions of witches' cauldrons. The ice cream, dangerous to eat while still "steaming," is allowed to rest until the liquid nitrogen is completely vaporised. Sometimes ice cream is frozen to the sides of the container, and must be allowed to thaw.
Making ice cream with liquid nitrogen has advantages over conventional freezing. Due to the rapid freezing, the crystal grains are smaller, giving the ice cream a creamier texture, and allowing one to get the same texture by using less milkfat. Such ice crystals will grow very quickly via the processes of recrystallization, thereby obviating the original benefits unless steps are taken to inhibit ice crystal growth.
For similar reasons, good results can also be achieved with the more readily available "dry ice" and authors such as Heston Blumenthal have published recipes to produce ice cream and sorbet using a simple blender.^[36]

See also

• Brain freeze
• Gelato
• Ice cream parlor
• List of ice cream brands
• Soft serve
• Frozen Yogurt