The degree of pasteurization heat treatment is relatively low, generally, it is heated at a temperature lower than the boiling point of water, and the heating medium is hot water.Different foods are pasteurized for different purposes. In some foods, especially milk, whole egg, egg white and yolk, pasteurization mainly destroys the possible pathogens, such as tuberculosis and salmonella. In addition, most foods, such as beer, fruit wine (wine) and fruit juice, adopt pasteurization to extend the shelf life of products from the perspective of microorganisms and enzymes.
Generally, pasteurized food still contains many microorganisms that can grow, usually thousands of live bacteria per ml or gram, which is shorter than the storage period of commercial sterilized products. Pasteurization technology is not only used in liquid food (juice, milk), acid food and canned jam, but also penetrates into other fields, for example, steam treatment of shelled oysters can reduce the number of bacteria in oysters. Its advantage is to treat food at a lower temperature and in a shorter time, so that the color, aroma, taste and nutrition of food can be protected from the damage caused by high temperature and long time processing.
It is mainly a sterilization method for milk, which can not only kill pathogens harmful to health, but also make milk quality change as little as possible. That is to say, according to the principle of the difference between the heat death curve of tubercle bacillus with strong high temperature resistance and the heat destruction curve of cream which is the most easily affected by heat, it is a method of heating treatment at low temperature for a long time or at high temperature for a short time. Among them, heating under 60 ℃ for 30 minutes ,as the standard of low-temperature sterilization, has been widely used in the world. Although high temperature treatment has some influence on the milk quality, it can strengthen the sterilization effect, this method is called high temperature sterilization, that is, above 95 ℃ heat for 20 minutes. In addition to milk, pasteurization can also be applied to fermented products.
Usually, the milk in bags sold on the market is produced by pasteurization. The fresh milk collected from the factory is treated at low temperature first, and then sterilized by pasteurization. The bagged milk produced in this way can usually be kept for a long time. Of course, the specific treatment process and process are much more complex, but the general principle is that.
It should be noted that drinking fresh milk is actually unsafe because it may contain bacteria harmful to our health. Another point is that pasteurization is not omnipotent either, the milk treated by pasteurization still needs to be stored at a lower temperature (generally < 4 ℃), otherwise, it is still likely to deteriorate. Therefore, many ways selling milk in bags on the market are not standardized.
Pasteurized milk is the most consumed milk in the world. In United Kingdom, Australia, the United States, Canada and other countries, the consumption of pasteurized milk accounts for more than 80% of the liquid milk, varieties are full skim , semi skim or full fat. In the U.S. market, virtually all milk is pasteurized milk, and it’s packaged in large packages (1 liter, 2 liter, 1 gallon),and people can buy a week’s worth of fresh milk at a time when they go to the supermarket. Few sterilized pure milk was sold in the market, and some small towns could not buy it at all.
Pasteurized fresh milk well preserves the nutrition and natural flavor of milk and is the best among all milk varieties.In fact, as long as the pasteurized milk is kept at a temperature about 4 ℃, the reproduction of bacteria is very slow, and the nutrition and flavor of milk can remain unchanged for several days.