# Pasteurized Milk Spoiling. **URL:** \ **Category:** Factual Questions\ **Created:** [November 14, 2006, 12:19am UTC](https://boards.straightdope.com/t/pasteurized-milk-spoiling/380326 "2006-11-14T00:19:31Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![Jim\_B](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jim_b/32/4338_2.png) [@Jim\_B](https://boards.straightdope.com/u/Jim_B)\ **Post date:** [November 14, 2006, 12:19am UTC](https://boards.straightdope.com/t/pasteurized-milk-spoiling/380326/1 "2006-11-14T00:19:31Z")
Why does pasteurized milk left in a sealed container still spoil? I mean, what then is the purpose of the pasteurization? And is pasteurization different from canning? Thank you in advance to all who reply 🙂 ---
**Author:** ![Antigen](https://avatars.discourse-cdn.com/v4/letter/a/848f3c/32.png) [@Antigen](https://boards.straightdope.com/u/Antigen)\ **Post date:** [November 14, 2006, 12:31am UTC](https://boards.straightdope.com/t/pasteurized-milk-spoiling/380326/2 "2006-11-14T00:31:40Z")
From the [Wiki page on Pasteurization](http://en.wikipedia.org/wiki/Pasteurization): > [@](#): > > Unlike sterilization, pasteurization is not intended to kill all micro-organisms (pathenogenic) in the food. Instead, pasteurization aims to achieve a “log reduction” in the number of viable organisms, reducing their number so they are unlikely to cause disease (assuming the pasteurized product is refrigerated and consumed before its expiration date). Commercial scale sterilization of food is not common, because it adversely affects the taste and quality of the product. Basically, not all the organisms are killed. Milk is something you keep in the fridge, and something you’re supposed to consume fairly quickly after it’s purchased, so there isn’t much chance for those few bacteria left behind to multiply and do much damage. Leave them in there long enough, though, and they will grow and take over, spoiling the milk. Milk that stays in the fridge the whole time will take a lot longer to spoil because the bacteria are slowed down by the temperature, but it will still happen eventually. ---
**Author:** ![SCSimmons](https://avatars.discourse-cdn.com/v4/letter/s/e495f1/32.png) [@SCSimmons](https://boards.straightdope.com/u/SCSimmons)\ **Post date:** [November 14, 2006, 4:00am UTC](https://boards.straightdope.com/t/pasteurized-milk-spoiling/380326/3 "2006-11-14T04:00:32Z")
Alas, pasteurization does kill the microorganisms that cause milk to go sour, which is a relatively benign process. It’s the pasteurization trade-off–drastically decreased likelihood of being sickened or killed by your milk, in exchange for increased difficulty in doing other neat things with it. If you want to make sour milk or cream, buttermilk, yogurt, cheese, etc. from pasteurized milk, you need to ‘seed’ it with a culture of the appropriate bacteria or mold. That’s the ‘cultured’ in the ‘cultured sour cream’ you find at the grocery store. ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [November 14, 2006, 4:36am UTC](https://boards.straightdope.com/t/pasteurized-milk-spoiling/380326/4 "2006-11-14T04:36:09Z")
OTOH, UHT milk is widely available and lasts quite a while unrefrigerated. > **[Ultra-high-temperature processing](https://en.wikipedia.org/wiki/UHT)** > > Ultra-high temperature processing (UHT), ultra-heat treatment, or ultra-pasteurization is a food processing technology that sterilizes liquid food by heating it above 140 °C (284 °F) – the temperature required to kill bacterial endospores – for 2 to 5 seconds. UHT is most commonly used in milk production, but the process is also used for fruit juices, cream, soy milk, yogurt, wine, soups, honey, and stews. UHT milk was first developed in the 1960s and became generally available for consu UHT mi...