The principle of sterilization is that within a certain temperature range, the lower the temperature, the slower the bacteria reproduce; the higher the temperature, the faster the reproduction. But if the temperature is too high, the bacteria will die. Different bacteria have different suitable growth temperatures and heat and cold resistance. In fact, pasteurization is to take advantage of the characteristics of pathogens that are not very heat resistant, and treat them with appropriate temperature and holding time to kill them all. However, after pasteurization, a small number of harmless or beneficial, heat-resistant bacteria or bacterial spores are still retained

A wide variety of pasteurization procedures are used today. Low temperature long time (LTLT) processing is a batch process and is now used only by small dairy plants to produce some cheese products. The "High Temperature Short Time" (HTST) process is a "flowing" process, usually performed in a plate heat exchanger, and is now widely used in the production of drinking milk. The products obtained in this way are not sterile, that is, they still contain microorganisms, and need to be refrigerated during storage and handling. "Fast pasteurization" is mainly used in the production of yogurt dairy products.

There are two main types of pasteurization methods used internationally:

One is to heat the milk to 62-65 ° C for 30 minutes. This method can kill various growth-type pathogenic bacteria in milk, and the sterilization efficiency can reach 97.3% ~ 99.9%. After sterilization, only some thermophilic bacteria, heat-resistant bacteria, and spores remain, but these Most of the bacteria are lactic acid bacteria, which are not only harmless to people but beneficial to health.

The other method is to heat the milk to 75 ~ 90 ℃ and keep it for 15 ~ 16 seconds. The sterilization time is shorter and the work efficiency is higher. However, the basic principle of sterilization is that it can kill the pathogenic bacteria. If the temperature is too high, there will be more nutrition loss.