Ultra-High Temperature (UHT) pasteurization and airtight sterilized containers allows milk to be kept at room temperature.
But how is this possible?
During the UHT process, the milk is pasteurized between 138°C and 158°C for a few seconds (eliminating pathogens and extending shelf life). Once it has cooled down, the milk is poured into a sterilized package without air contact.
The packaged milk can be found in a ‘tetra pak’ but also sealed plastic bottles. Note that in Canada, sealed plastic bottles of UHT milk are found in the refrigerated section of your store, alongside other fresh milk.
Those sealed bottles have a best before date that are a few months after the time they are packaged.
As long as the package remains closed, the milk does not have to be refrigerated. It can be stored at room temperature until the best before date (pretty neat, eh?). Once opened, UHT milk should be placed in the refrigerator and consumed within the next 3 days.