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There are millions of bacteria in each cubic centiliter of milk or most other liquids.

Many come just from being exposed to the air, so milk starts to turn sour as soon as it is milked.

Refrigeration is a way to contain the development and reproduction of these bacteria.

Pasteurization is a way to get rid of the nefarious bacteria, but it doesn't get rid of those that cause souring, for instance. It just postpone it for a few more days compared to raw milk.

The UHT (Ultra high Temperature) process does a better job, increasing the shelf life to several weeks without requiring refrigeration, at the cost of a burned taste.

Modern milking processes limit the exposure to ambient air using vacuum pumps and a neutral gas such as nitrogen, and refrigerating the milk immediately after milking, so our milk keeps longer than it ever did.

Shopping using home delivery is also a way to ensure that the "cold chain" is not interrupted, like when you shop in a supermarket and carry refrigerated milk in an unrefrigerated caddy or the boot of the car. Each minute spent unrefrigerated means tens of thousands of bacteria reproduce.

The souring process is caused by bacteria that convert the lactose sugar of the milk into lactic acid. They do so even in the fridge, just much slower.

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12y ago
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12y ago

Because It has less preservatives and whole milk is ultra pasteurized While skim is only pasteurized. I hope this helped you.

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Wiki User

12y ago

Well, sorry to burst your bubble but, its the same thing!

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Q: Why does milk expire quickly?
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