: Why do some milk need to be kept refrigerated and some don’t?

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Why some milk need to be kept in the fridge or chiller and some could just be kept in shelves?

In: Chemistry
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If the milk is Pasteurized, then it can be held in the fridge for a few days, mostly 3. During that process, the milk is heated and the bacterial activity is reduced. But the bacteria are still alive. If you keep it in the fridge, it would take much longer for the bacteria to make the milk go bad.

But during the sterilization process, the bacterial are completely “sterilized”, meaning they cannot reproduce and “spoil the milk” until the bottle/pack is open. Once it’s open, it should be kept in the fridge. Usually, sterilized milk is kept in special packets (One of the famous brands being Tetra Pack) which has several different layers. Until it is opened, it can be stored in room temperature.

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Edit: In my country, depending on the brand and the time of the year (Winter/Summer) Pasteurized milk can be kept for 3 to 5 days. It depends on many factors, including storage, delivery, ambient temperature, etc.