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How does the shelf life of milk come? When you stand in […]
How does the shelf life of milk come? When you stand in front of the freezer, you will find some details on the milk carton-the production date is February 15, 2013, the shelf life is 30 days, and the refrigeration temperature is recommended to be 4 ℃, which is commonplace. Numbers that are often overlooked by us. How are these standards set? Do you know how to pick them?
The most ideal way is of course to conduct an actual measurement, but you must first determine the approximate time range and figure out several factors that affect the shelf life of milk. These are the characteristics of milk itself, processing technology, packaging form and freezer storage conditions.
Taking the temperature of the freezer as an example, the normal storage condition is 7 ℃, which will be set to 21 ℃ in the accelerated test. In this way, the shelf life obtained can be reversed by the formula to obtain the shelf life that can be achieved under actual conditions. At the same time, a normal shelf life test is also conducted to verify whether the results are reliable.
The shelf life of freezer milk is not an absolute critical point. Food will have different chemical changes under different environmental conditions. If the environment is harsh, such as extreme heat and cold, the shelf life cannot be used as an absolute safety standard; on the contrary, if the normal storage is performed according to the requirements on the packaging, and no deterioration problems are found, milk that has expired for one or two days is not inedible.
Fresh milk does not refer to the milk that has just been squeezed out, because the fresh milk that has just been squeezed out will start to grow bacteria after about 2 hours of exposure to the air, and the bacteria will deteriorate.Generally, it will be kept in the freezer within 15 minutes after extruding the fresh milk And sent to the processing plant for further disinfection. So the so-called fresh milk you buy in the freezer is sterilized. The shelf life of different milks is also related to the sterilization and packaging methods they use.
Milk with a short shelf life and simple packaging—such as bottled milk—is mostly processed by pasteurization. The method is to heat the milk to 62 ℃ to 65 ℃ and hold for 30 minutes, or to 75 ℃ to 90 ℃, hold for 15 to 16 seconds.
The milk sterilized by this method, the bacterial spores are not inactivated, so it should be stored in the freezer at low temperature, generally 4 ℃, in this environment, it can be kept fresh for about 1 week.
Another treatment method is called ultra high temperature sterilization, also called UHT milk, that is, the milk is placed at 135 ℃ to 140 ℃, heated for 1 to 2 seconds, and then quickly freezer cooling. This practice is commonly used for bagged milk with a long shelf life. Its disadvantage is that some heat-resistant nutrients such as vitamins in milk will be destroyed, but because of the short time of high temperature, this technology generally has little effect on nutritional value.
Secondly, aseptic packaging is also an important step. Milk must not be exposed to light and air during the entire operation, so as to maintain its storage requirements at room temperature and without the need to add preservatives. Adding preservatives may not only result in extra input costs, but also may damage the entire aseptic process. The shelf life of milk after ultra high temperature sterilization can reach 1 to 6 months.