At the dairy processing plant, the milk is pumped to refrigerated storage tanks. It is pumped to the pasteuriser, where it is heated to 72°C for 15 seconds and then cooled to 4°C very rapidly.
This process, called pasteurisation, kills any harmful bacteria that may be present in the milk and is required by law in South Africa. The process of pasteurisation was discovered in 1868 by the French scientist, Louis Pasteur (1822–1894).
Another form of making milk safe for consumption is to provide extended shelf life milk (ESL). ESL milk is milk that has been treated in a manner to reduce the microbial count beyond pasteurisation. ESL milk is packaged under extremely hygienic conditions and has a longer shelf life than fresh pasteurised milk when kept at a temperature of 0–5°C.
Ultra-high temperature (UHT) treatment allows milk to stay fresh and safe for a long time. The milk is heated to above 125°C and then packaged aseptically. The end product is free from any micro-organisms or spores that could cause spoilage. The UHT process is quick, so very few vitamins are destroyed. UHT-treated milk, also referred to as long-life milk, can be kept at room temperature in the sealed packaging for many months without going sour. Once the package has been opened, the milk must be kept cold and used in the same way as fresh milk.
Milk may also be homogenised to improve the fat distribution. Homogenisation forces the milk fat through a very small nozzle. at high speed and breaks the fat drops into smaller droplets. This keeps the fat droplets evenly distributed in the milk.