Milk is considered one of the most nutritious foods that are consumed by people worldwide. The milk undergoes processing to increase the variety of nutrients. The processing of milk includes various operations ranging from collecting milk from the farm, storing milk in tanks, separating, pasteurizing and homogenizing to improve the quality of the milk. The milk processing equipment typically consists of milk tanks that are used to store all kinds of milk raw, skimmed or cream, pasteurizers where the bacteria in the milk are killed and enzymatic activity is reduced, separators which prevent the entry of destructive air after pasteurization to ensure product quality and homogenizers that improve the taste, texture and other organoleptic properties of the milk. The result of all these operations is good quality milk.
Steps involved in milk processing
Steps involved in milk processing are:
- Milking is done twice a day, the process is mechanical in big farms. Temperature and taste of the milk is checked at this stage
- The milk is transferred to large refrigerated tanks in which it is transported to the processing units through huge trucks
- Separation and clarification of the milk takes place in separators to separate milk from germs and useless remains
- Fortification of milk with minerals and vitamins takes place after separation and clarification
- Pasteurization of the milk takes place which involves heating the milk to kill harmful microorganisms
- Homogenization removes fat from the milk
- Milk is then packed in cartons or plastic covers. Labelling is done with the expiry date and the packs are distributed to different states
Pasteurization refers to the process of heating a liquid to below the boiling point to destroy microorganisms. The process was named after its developer, Louis Pasteur who implied it initially to improve the keeping quality of the wine. Commercial pasteurization of milk gained its importance in the late 1880s in Europe and the early 1900s in the USA. Common milk-borne diseases such as typhoid, scarlet fever, septic sore throat, diphtheria and diarrhoea can be virtually eliminated by implementing pasteurization.
The main motto behind pasteurization was to control tuberculosis causing bacteria, which is no longer a concern as cows are tested for TB annually and removed from herds and treated if shown positive. However, the need for pasteurization persists as milk acts as a rich medium for the growth of various pathogenic bacteria such as Salmonella spp., Escherichia coli and Listeria monocytogens. The PasLite test is universally accepted by dairy industries and food manufacturers to confirm if the milk products are properly pasteurized. This test detects the presence of alkaline phosphatase, an enzyme that is naturally present in the milk and destroyed by the heat and holding period of pasteurization.
Pasteurization can be a batch or continuous process. The pasteurization conditions that are in use today are 62.8C for 30 minutes for a batch process or 71.7C for 15 seconds for a continuous process. However, different milk products have different conditions for pasteurization. Continuous high-temperature Short Time (HTST), Continuous Higher Heat Shorter Time (HHST), continuous ultra-pasteurization and aseptic Ultra High Temperature (UHT) are various types of pasteurization. Canned products are usually sterilized at 115.6C for 20 mins.
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