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 Mono Stearate – 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.
To know more about ice cream, its legal standards and nutritive value, read ICE CREAM
The author is a dairy expert, specializing in the technology and microbiology of dairy foods and holds a doctoral degree in Dairy Science; for more info on milk and dairy products please visit her site A Professional Dairy Site