Milk (Dairy) Processing

Milk is a fluid secreted by the mammary glands of healthy cows of the bovine species during the usual lactation period by means of complete and regular milking. It is a concentrated food, designed to initially protect the newly born animal by supplying concentrated antibodies to counter disease until the immune system of the young animal is fully functional, and thereafter also to ensure rapid growth until the young are more independent.

Milk is a valuable nutritious food that, if untreated, will spoil within a few days. However, there are a number of preservation techniques that can be used at a small scale to extend its shelf life by several days, weeks or months. Some of these processing methods also produce foods that have different flavors and textures, which can increase the value of the milk when these products are sold.

Milk Processing Divisions

Pasteurized milk, Butter and ghee, Soured milk and yoghurt, Cheese – making, Ice cream production and Dairy confectionery. Other methods of milk processing are making dried milk powder, sterilized milk (Ultrahigh-Temperature or ‘long-life’ milk and bottled sterilized milk), canned (evaporated or condensed) milk, or milk by-products such as casein.

Spoilage, food poisoning and preservation

Milk is not only nutritious for people, but also for bacteria. Because milk is a low acid food, bacteria are able to grow in it and contaminate any products that are made from it. If milk is not properly processed or if it is contaminated after processing, bacteria can change the flavor, texture or color of dairy products, to spoil them and make them unacceptable for sale. Other dangerous bacteria can grow in milk and cause food poisoning. Illnesses such as tuberculosis, brucellosis and typhoid fever can also result from using poor quality milk or milk that is not properly processed.

Methods of processing

There are four main Steps used to process milk:

Cooling fresh milk at 4º C to extend the shelf life by a day or two.

Heating milk to destroy both contaminating micro-organisms and naturally occurring enzymes that change the flavor of milk.

Pasteurization

There are regulations in most countries that specify the time and temperature that milk should be heated to pasteurize it. Most specify that milk should be heated to 63oC for 30 minutes. Higher temperatures and shorter times are used in larger commercial operations but the equipment needed to do this is more expensive

Making the milk acidic to slow down or prevent the growth of spoilage bacteria or food poisoning bacteria (this also changes the milk to a curd).

Reducing the amount of water in milk products to slow down or prevent the growth of bacteria. This may be combined with adding sugar (to make milk confectionery) or salt (in cheese or butter production), both of which also prevent bacteria from growing.