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.
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
- A decrease in temperature favours rapid crystallization insofar as it increases the supersaturation.
- 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.
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.
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.
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
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