Insights on Ice Cream and its Production Process

 Ice cream (derived from iced cream or cream ice) is a sweetened frozen food which is typically eaten as a dessert. It is usually made from dairy products such as milk and cream, combined with fruits and nuts, flavourants, stabilizer, emulsifiers, colorants. The mixture is stirred to incorporate air and cooled below the freezing point of water to prevent the formation of ice crystals. Without air, ice cream becomes heavy and soggy.

  

                                                                     

Ice Cream can also be defined as a frozen emulsion of air bubbles, ice crystals, milk fat globules, colloidal proteins, and gums suspended within viscous syrup, the continuous phase. Some components of the continuous phase, especially the lactose (milk sugar), are in the supersaturated state (as shown in the below figure). Under certain conditions, lactose may crystallize in the frozen product, causing a sand-like feeling in the mouth.

A wide variety of ingredients are allowed in ice cream but there should be a minimum amount of milk fat, milk solids and air as defined by Standards of identity in U.S Code of Federal Regulations(CFR). Ice cream must contain at least 10% Milk fat, 20% milk solids. Ice cream is of different types depending upon the amount of fat present in it. It may be of reduced fat( 25% less fat than reference ice cream), light(50% less fat than reference), low-fat (less than 3g fat per serving) or nonfat(less than 0.5g per serving). Both artificial and natural sweeteners can be used as a sweetening agent. Besides providing characteristic sweetness to ice creams, they also tend to lower down the freezing point of the mix so that some amount of water remains unfrozen while serving.

According to Food Safety and Standard Regulations 2011, Ice Cream, Kulfi, Chocolate Ice Cream or Softy Ice Cream (hereafter referred to as the said product) means the product obtained by freezing a pasteurized mix prepared from milk and /or other products derived from milk with or without the addition of nutritive sweetening agents, fruit and fruit products, eggs, etc. The product shall conform to the compositional specifications provided in the table below:

Requirement	Ice cream	Medium Fat Ice cream	Low Fat Ice cream
Total Solid	Not less than 36%	Not less than 30%	Not less than 26%
Weight/volume (g/l)	Not less than 52%	Not less than 47%	Not less than 47%
Milk Fat	Not less than 10%	More than 2.5% but less than 10%	Not more than 2.5%
Total Protein	Not less than 3.5%	Not less than 3.5%	Not less than 3%

Frozen Dessert or Frozen Confection means the product obtained by freezing a pasteurized mix prepared with edible vegetable oils or fats, having a melting point of not more than 37 ⁰C or vegetable protein products, or both. It may also contain milk fat and other milk solids with the addition of nutritive sweeteners and other permitted non-dairy ingredients. The said product may contain incorporated air and may be frozen hard or frozen to a soft consistency. Therefore, as per regulations Ice Creams do not contain edible vegetable oils or fats or vegetable proteins but Frozen Desserts do.

Structure of Ice cream | Components of Ice cream

a)      Serum- It contains dissolved sugars and salts as well as any aqueous phase proteins and stabilizers. It is the serum which forms lamella between the other structures such as ice, air, fat globules, micelles etc.

b)      Ice crystals- Since ice cream is a frozen dessert hence ice crystals become an integral component of ice cream. The ice crystals should be sufficiently small to provide a smooth mouth feel. The amount and size of ice crystals affect numerous attributes of the finished product, from scoop ability and hardness to cooling effect and meltdown rates.

c)      Air cells- More than half of the volume of ice cream is air which provides light texture to it. The average size of air cells lies in the range of 20-25 micrometer.

d)     Fat globules and clusters- The average size of emulsion droplets is about 0.8 micrometer. After freezing, fat globule clusters are formed as a result of partial coalescence of individual globules. The average size of clusters ranges between 70-80 micrometer. Fat globule clusters are one of the most important parameters that determine shape retention properties and meltdown rates.

e)      Protein/ stabilizer structure- Various stabilizers (proteins and gums) used in ice creams take on structure and orientation depending upon nature of molecule with the other components of ice cream, some may become weak gel other may be dissolved in the liquid phase. Interactions between dairy proteins and stabilizers greatly affect ice cream characteristics.

Air In Ice Cream

Air forms, one of the most important ingredients in ice cream. Usually, air makes up 30-50% volume of ice cream. The amount of air that is added in ice cream is called overrun. If the volume of ice cream is doubled by adding air then overrun is 100% which is the maximum allowed air in ice creams. If the amount of air in ice cream is more, then it would melt faster than ice cream with less air. Less expensive ice creams generally contain more air.

Approximate  Composition Of Ice Cream (Percentage By Weight) -

CONSTITUENT	DAIRY ICE CREAM
Milk fat	10
Nonfat milk solids	11
Added sugar	14
Additives	0.4
% Overrun*	100
Edible energy(KJ/100 ML)	390

           *Overrun means relative increase in volume by air beaten in.

Ice Cream Terminology

Depending on the filling method, ice cream products fall into one of the following categories:

MOULDED

Ice cream or water ice mix is filled into moulds and frozen to produce stick novelties. After extraction, the products can be dipped in chocolate or other coatings.

FILLED

Ice cream is filled into cups, cones or containers/tubs, often combined with more flavours and may be decorated with chocolate, cream, ripple and dry materials.

EXTRUDED

Ice cream is typically extruded onto a tray by means of extrusion with a cutter. A wide variety of products can be produced including stick novelties, sandwiches, desserts, ball-top cones and so on. Extrusion technology provides the possibility to work with ice cream drawn at much lower temperature where the viscosity of the ice cream is high due to more water being frozen into ice crystals. This generates ice creams that are both smoother due to smaller ice crystals and creamier due to higher churning of fat compared to moulding and filling technologies. The higher viscosity also offers the possibility to work with detailed forms and flavours, decorations and coatings.

Raw Materials and Ingredients

The ingredients used in ice cream production are:

• Fat
• Milk solids non-fat (MSNF)
• Sugar/non-sugar sweetener
• Emulsifiers/stabilizers
• Flavours
• Colours
• Other ingredients

FAT

Fat makes up about 10 to 15% of an ice cream mix and may be milk or vegetable fat. The fat gives creaminess and improves melting resistance by stabilizing the air cell structure of the ice cream. Milk fat is used in the form of whole milk, cream, butter or anhydrous milk fat (AMF). Milk fat can be replaced by vegetable fat, where refined or hydrogenated (hardened) coconut oil and palm kernel oil are most commonly used. The use of vegetable fat in ice cream is regulated by legislation in many countries. Fat imparts a characteristics richness and mellows the flavour of ice cream. It tends to retard the rate of whipping. Lecithin contained in milk fat has important contribution to the flavour and tactual qualities of ice cream. It contributes to smoothness of texture and contributes to body and melting resistance of the product. It does not lower the Freezing point (FP) of mix.

MILK SOLIDS-NON-FAT (MSNF)

MSNF consist of proteins, lactose and mineral salts derived from whole milk, skim milk, condensed milk, milk powders and/or whey powder. In addition to its high nutritional value, MSNF helps to stabilize the structure of ice cream due to its water-binding and emulsifying effect. The same effect also has a positive influence on air distribution in the ice cream during the freezing process, leading to improved body and creaminess. In a well-balanced recipe, the quantity of MSNF should always be in proportion to the water content. The amount of MSNF generally varies inversely with the fat content of the mix and ranges from 7.5-8.0% in an 18% fat ice cream to 14.0% in a 4% fat ice milk mix. Indian PFA regulation does not permit less than 10.7% SNF by specifying a minimum of 3.5% protein content. The limiting factor for MSNF is occurrence of ‘sandiness’ defect in ice cream. As a thumb rule, the MSNF should not be more than 15.6-18.5% of the TS in the mix; based on the turnover (slow or rapid).

SUGAR

Sugar is added to increase the solids content of the ice cream and give it the level of sweetness consumers prefer. Ice cream mix normally contains between 12 to 20% sugar. Sugar is the common description for the saccharides, including the monosaccharides (i.e. glucose/dextrose and fructose), disaccharides (i.e. sucrose and lactose (milk sugar)) and starch derivates (i.e. glucose syrup, glucose/fructose syrup and high fructose syrup). The consistency of the ice cream can also be adjusted by selecting different types of sugar. This makes it possible to produce ice cream that is easy to scoop. In the production of sugar-free ice cream, sweeteners are used to replace sugar. Aspartame, acesulfame K and sucralose are the most commonly used sweeteners in ice cream and are applied in conjuction with a bulking agent such as malto-dextrin, poly-dextrose, sorbitol, lactitol, glycerol or other sugar alcohols.

EMULSIFIERS AND STABILIZERS

Emulsifiers and stabilizers are typically used as combined products at dosages of 0.5% in the ice cream mix. Traditionally, these products were produced by dry blending, but today integrated products are preferred due to the improved dispersion and high storage stability.

Emulsifiers

Emulsifiers are substances that assist emulsification by reducing surface tension between two phases. There exists several different emulsifier types utilized in ice cream production, but the far most dominant and probably most effective emulsifier is the mono/di glyceride of fatty acids. The mono/di glyceride is often derived from a vegetable fat (triglyceride) where fatty acid chains have been removed, creating a molecule that has a lipophilic end (fat loving) and a hydrophilic part (water loving). The mono-/di glyceride has two main functions during ice cream processing, where it assists the dairy protein displacement from the fat surface membrane, in order to improve the churning during the freezing process. The mono/di glycerides also seed the crystallization of fat, which is essential for avoiding over churning of the fat during the freezing process. Egg yolk is a well-known emulsifier, but is expensive and less effective than the most commonly used types.

Stabilizers

A stabilizer is a substance that has the ability to bind water when dispersed in a liquid phase. This is called hydration and means the stabilizer forms a matrix that prevents the water molecules from moving freely. Most of the stabilizers utilized for ice cream are large molecules derived from seeds, wood or algae/seaweed. Stabilizers are used in ice cream production to increase the viscosity of the mix and create body and texture. They also control the growth of ice crystals and improve melting resistance.

FLAVOURS

Flavours are a very important factor in the customer’s choice of ice cream and can be added at the mixing stage or after pasteurization. The most popular flavours are vanilla, chocolate and strawberry. In the EU, flavours are classified in three groups: natural, nature-identical and artificial. Nature-identical flavours are the most commonly used. The most common ice cream flavours are vanilla, nougat, chocolate, strawberry and nut.

COLOURS

Natural or artificial colours are added to the mix to give the ice cream an attractive appearance. Local legislation exists in most countries regarding the use of colours in food.

OTHER INGREDIENTS

Many moulded and extruded ice cream products are coated with chocolate. Two types of chocolate coatings are used: real chocolate and chocolate compound. The cocoa mass and butter are replaced with a blend of cocoa powder and vegetable fat in the chocolate compound. Dry ingredients are either added through an ingredient doser or as top decoration matter on cones, cups and bars. A great variety of products are used: chocolate, nuts, dried fruit pieces, candies, cookies, smarties, caramel pieces, etc.

Ice Cream Processing Flow Chart

 Fig. Process flow diagram for ice cream manufacturing

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

1.   Blending of the mix ingredients
2.   Pasteurization
3.  Homogenization
4.  Aging the mix
5.  Freezing
6.  Packaging
7.  Hardening
8.  Storage.

How Is Ice Cream Made | The Production Process

Blend the ice cream mixture- The milk fat, milk solids, stabilizers, emulsifiers are blended together for uniform mixing of dry ingredients with liquid for 6-8 minutes.

Pasteurize mix- The ultimate aim of pasteurization is to kill the pathogenic microorganisms and to prevent spoilage. Moreover, the lipase enzymes present in the mix also need to be deactivated because it may also be present at low temperatures. Additives added after homogenization, are pasteurized separately. Pasteurization is usually done at 80 degree Celsius for around 25 seconds. Since the viscosity of ice cream mix is greater than liquid milk, therefore the conditions used for the pasteurization of ice cream mix, is higher than liquid milk.

Homogenization- Ice cream mix is homogenized (2500-3000 psi) to break down the large fat globules into a smaller one so as to form a better emulsion. Homogenization is especially meant to give ice cream fine and smoother texture.

Cooling and Ripening- The ice cream mix are cooled rapidly within the range of 32-40 Fahrenheit before freezing so that the milk fat globules get partially crystallize before entering into the freezer, moreover, it gives protein stabilizers time to hydrate. This improves whipping properties of the mix. Some added emulsifiers need considerable time at low temperature to displace protein from fat globules. The process of holding the ice cream mix prior to freezing is called aging which might last for up to 24 hours. The physical changes that occur during aging are beneficial to its freezing properties.

Addition of liquid flavors and colors- Only the ingredients that are liquid can be added before freezing to make sure that mix flows properly through freezing equipment. The flavor intensity imparted by flavors should be delicate but definite, pleasing but not overpowering. Combination of flavors can also be added depending upon the requirement and consumer acceptance.

Freezing- This process involves freezing the mix and incorporation of air. Ice cream mix can be frozen either in the bath or continuous freezers. The continuous freezing process is much faster than batch process. The freezing process and incorporation of air should happen simultaneously. If the bulk of the water is frozen after that any beating of air becomes impossible and freezing after air is beaten will lead to the insufficient churning of fat globules and can damage foam structure.

Addition of fruits, nuts and bulky flavorings (candy pieces etc.) - fruits, nuts and bulky flavourants are added at this point. These ingredients should not be added before freezing because they would interfere with the smooth flow of ice cream mix. Moreover, the addition of these bulky ingredients after freezing prevents the damage to the large pieces or chunks.

Packaging- The cartons are filled with the premeasured amount of ice cream at the rate of 70-90 cartons per hour. The machine places the lid on each carton and pushes them into the conveyor belt. The cartons then pass under ink jet that sprays paint expiration date and production code onto each carton. The packaging of ice cream is a complicated process especially if ice creams of certain shapes are required.

Hardening- It is an important process which helps the ice creams to retain their shapes and provide a certain required shelf life with respect to chemical and enzymatic reactions. The packaged ice cream is passed to hardening tunnel in which very cold air below – 25-degree Celsius is passed for 20 minutes. Rapid cooling of ice cream promotes quick freezing of water to create small ice crystals. Storage of ice cream at -25 degree Celsius helps to stabilize ice crystals and thus maintain its quality.