pasteurizer working principle
The principle of the pasteurizer is the pasteurization method, which is a cold sterilization method invented by the French microbiologist Pasteur. Changed disinfection method.
Generally, the suitable temperature for microbial growth is 28℃-37℃. If the temperature is too high, the bacteria will die. Pasteurizer is a type of food that heats milk and other foods to 60-65°C, keeps it for 30 minutes to sterilize, and then rapidly cools the temperature to 4-5°C for storage. This kind of sterilization, which is mostly used in milk, can not only kill pathogenic bacteria, but also reduce nutrient loss. However, this disinfection method cannot kill all bacteria and microorganisms, so the shelf life is very short.
Within a certain temperature range, the lower the temperature, the slower the bacterial reproduction; the higher the temperature, the faster the reproduction (generally the suitable temperature for microbial growth is 28°C-37°C). But the temperature is too high and the bacteria will die. Different bacteria have different optimal growth temperature and heat and cold tolerance. Pasteurization actually uses the characteristics of pathogens that are not very heat-resistant, and treats them with appropriate temperature and holding time to kill them all. However, after pasteurization, a small part of harmless or beneficial, relatively heat-resistant bacteria or bacterial spores are still retained. Therefore, pasteurized milk should be stored at a temperature of about 4 °C, and can only be stored for 3 to 10 days. Up to 16 days.
There are a wide variety of pasteurization procedures in use today. The "low temperature long time" process is a batch process that is only used today by small dairies to produce some cheese products. The "high temperature short time" treatment is a "flow" process, usually carried out in a plate heat exchanger, and is widely used in the production of drinking milk today. The product obtained in this way is not sterile, ie still contains microorganisms, and requires refrigeration during storage and handling. "Rapid pasteurization" is mainly used in the production of yogurt dairy products. There are mainly two kinds of pasteurizer high temperature disinfection methods commonly used in the world.
One is to heat the milk to 62~65℃ 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 disinfection, only some thermophilic bacteria, heat-resistant bacteria and spores remain, but these Most of the bacteria are lactic acid bacteria, and lactic acid bacteria are beneficial to human health.
Another method is to heat the milk to 75~90℃ and keep it warm for 15~16s, which has a shorter sterilization time and higher work efficiency. But the basic principle of sterilization is that the pathogenic bacteria can be killed, but if the temperature is too high, there will be more nutrient loss.