Pasteurisation is commonly associated with milk, however, did you know that it was originally created to preserve wine and beer and prevent them from getting sour?
The world of science attributes Louis Pasteur as the inventor, thus, the process was named after him. As a microbiologist, he found the ideal temperature and length of time to heat wine and beer without destroying the flavours.
Franz von Soxhlet suggested that milk should be pasteurised to remove harmful microorganisms. Raw milk brought many illnesses such as streptococcal infections, tuberculosis, typhoid fever, food-borne illnesses and diphtheria. For this reason, milk pasteurisation became a regular process until today.
Common Causes of Milk Contamination
Milk contamination can be due to several reasons. If a cow is sick, it can transfer harmful microorganisms to the milk. If a cow has mastitis, it can also contaminate the milk expressed from the infected udder. In addition, there are many bacteria present in a cow’s skin. It can easily be transferred during milking. Other causes are mostly environment-related such as physical contamination of the cow’s faeces, dirty equipment, dirt, insects and rodents. Cross-contamination from human clothing and shoes can also cause milk contamination.
Purpose of Pasteurisation
Unlike sterilisation, the method of pasteurisation only reduces the number of pathogens. It does not kill all microbes found in food and beverages. The temperature used to heat the liquid is below boiling point. This is to prevent altering the physical appearance and flavour of food.
Another reason for pasteurising liquid is to help preserve food. Shelf life could vary according to the type of pasteurisation process. Pasteurising using lower temperature would entail a longer heating time. Using higher temperature, on the other hand, requires shorter heating time.
Methods of Milk Pasteurisation
The oldest method of pasteurising milk is known as batch or vat pasteurisation. In this process, milk is heated at 63 deg C (155 deg F) for 30 minutes. This is the simplest of all methods since it can be done at home using a stovetop. Vat is also referred to as low temperature, long time pasteurisation.
High temperature, short time pasteurisation (HTST) uses 72 deg C (161 deg F) to heat milk for 15 seconds. The milk passes through metal plates or pipes heated on the outside by hot water. HTST is also called as flash pasteurisation.
Ultra heat-treating pasteurisation (UHT) uses a temperature of 138 deg C (280 deg F) to heat milk for at least two seconds. UHT processed food and beverages can stand without being refrigerated. UHT-processed milk is those commonly seen in cartons and displayed in shelves.
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Extended shelf life (ESL) milk undergoes any of these methods – direct heating, indirect heating, micro-filtration, modified pasteurisation and deep bed filtration. Compared to UHT milk, it needs to be refrigerated to a temperature of eight deg C or below to preserve its quality.
