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Milk itself is a very humid environment, and the protein and lactose in it provide sufficient nourishment for bacteria. Regular packaged milk is sterilized. (But raw milk doesn't!) The risk of drinking untreated freshly milked cows is very high! ）
Unopened milk, the storage conditions vary depending on the sterilization process.
"Fresh milk" should be put in the refrigerator
The so-called pasteurization, the tradition is to use a temperature of about 62 ° C to heat for about 30 minutes, the current more common is to use a temperature of about 75 ° C to heat about 15 seconds. This can kill most of the microorganisms in the milk, and the taste of the milk and the heat-sensitive vitamins in it are well preserved.
Such milk packaging will have three big words on it: "fresh milk" or "fresh cow's milk". Although there are no pathogenic bacteria such as Salmonella in products that meet the standards, there are still a small number of other colonies in them, which need to be refrigerated and stored in an environment of 2-6 ° C to avoid bacterial multiplication.
Even if the fresh milk is not opened, it must be placed in the refrigerator, the shelf life is between 5-7 days, according to the specific process there will be some differences, subject to the product packaging.
In addition to pasteurized milk, there is now a kind of high-temperature sterilization milk on the market, the temperature used for sterilization is higher than that of pasteurization (typical one is 95-110 ° C, 2-4s), the shelf life of unopened can be extended to about 15 days, the packaging of this milk is often marked "milk" or "milk", but the brand name often has the word "fresh", and it should also be stored in the refrigerator.
"Pure milk" can be stored at room temperature
Products marked with the words "pure milk" use ultra-high temperature sterilization technology, which is heated for 2 seconds at a high temperature of about 135 ° C, which can basically kill all microorganisms in milk. Without opening, the shelf life is usually 6-12 months.
Once the seal is opened, drink it as soon as possible
Pasteurized milk, high temperature sterilization milk, ultra-high temperature sterilization milk, from the perspective of obtaining protein and calcium, there is no significant difference, the shelf life of unopened is increasing in turn, the taste (including price) may be decreasing in turn, and the choice of weighing their own needs can be.
But no matter what kind of milk, once opened, it comes into contact with bacteria in the environment and becomes a potential bacterial medium.
If you can't drink it after opening, you should close the lid and put it back in the refrigerator and drink it within the time limit specified in the packaging instructions. Including self-brewed milk, leaving it at room temperature for too long is also at risk of spoiling.
The packaging is really well written
Resources:
Meng Xianwen. Research on heating method of Tetra Pak aseptic packaging products[J].Packaging Engineering,2007(02):52-54.
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