Pasteurization, also known as low-temperature sterilization, cold sterilization, is a kind of disinfection method that uses a lower temperature to kill bacteria while preserving the flavor of nutrients in the product. It is often broadly used to define the heat treatment method that needs to kill various pathogens.
Pasteurization is to heat the mixed raw materials to 68-70 ℃ and keep the temperature for 30 minutes, then rapidly cool them to 4-5 ℃. Generally, the lethal point of bacteria is below 68℃ and time is below 30min, so after the mixed raw materials are treated in this way, pathogenic bacteria and most non-pathogenic bacteria can be killed; the mixture is heated and then suddenly cooled, and the drastic changes in heat and cold can also contribute to the death of bacteria.
In a certain temperature range, the lower the temperature, the slower the bacterial reproduction; the higher the temperature, the faster the reproduction (the suitable temperature for the growth of general microorganisms is 28 ℃ – 37 ℃). But if the temperature is too high, the bacteria will die. Different bacteria have different optimum growth temperature, heat, and cold tolerance. In fact, pasteurization is to take advantage of the pathogen is not very heat-resistant characteristics, with the appropriate temperature and heat preservation time treatment will kill all of them.
However, after pasteurization, a small number of harmless or beneficial, relatively heat-resistant bacteria or bacterial spores are still retained, therefore the pasteurized milk should be kept at a temperature of about 4℃, and can only be kept for 3-10 days, up to 16 days.