The most commonly used pasteurization method is HTST, that is, the raw milk is heated to 70℃ ~ 72℃, 12 ~ 15 seconds. The process of pasteurization can be divided into the following six processes: using the waste heat of freshly processed fresh milk to heat the raw milk that has just arrived, which can be heated to about 57℃. Heat the milk to 72℃ through a hot water pipe and keep it for a specified time. At 72℃, the holding time shall not exceed 65438 05 seconds. The actual production process is to send raw milk into the pipeline, control the flow of milk, and ensure that the heating temperature of milk reaches 72℃ and the accurate duration. Then, the milk is transported to the other end of the first-stage system, where the new raw milk is preheated and cooled by itself. Cool the hot milk to about 57℃ in the heat exchanger. After cooling, continue to cool the milk to 24℃ with cold water. Depending on the cold water supply conditions and seasons, it may be slightly higher or lower. In the final stage, the milk is cooled to 3℃. The temperature of the filled milk is kept at 4℃ ~ 6℃, and it can be sold from the dairy factory. All pasteurization methods take mycobacterium tuberculosis as the control index of microorganisms. In actual production, the elimination of all tuberculosis bacteria means the elimination of all other germs. Pasteurization can also destroy all yeast, mold and bacteria in milk and most plant cells. After pasteurization, fresh milk will also deteriorate. In addition to photocatalytic oxidation and the deterioration of oil by various enzymes in milk, corruption is mainly caused by the reproduction of bacteria. It rarely turns sour and caked, which is usually caused by lactic acid bacteria.

Lactic acid bacteria will produce lactic acid in the temperature range of 10℃ ~ 37℃. When the temperature exceeds 37℃, fresh milk will even produce a lot of volatile substances, giving off a rancid smell; A so-called "violent fermentation" will produce a variety of gases, which are caused by Escherichia coli; In warm climate, "thin cream condensation" and "low acidity condensation" often occur, and small pieces of fat float on the surface of milk; "Sticking milk" occurs because the bacteria in milk multiply as soon as it leaves the milk of livestock, so all tools and containers must undergo strict disinfection and sterilization; The bitter taste of fresh milk is the result of some microorganisms attacking the protein and fat in milk and making it deteriorate. Butyric acid is produced in fresh milk, and corruption is caused by lipase or some molds and bacteria in milk. And so on, there are various forms of corruption in fresh milk, so effective sterilization and protection measures must be taken to ensure the quality of fresh milk.