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What is Pasteurized Milk?

Mary McMahon
Updated May 17, 2024
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Pasteurized milk is milk which has been heat-treated to kill pathogens which cause disease. Not all pathogens are removed during the pasteurization process, so pasteurized milk is not 100% sterile, but many people consider it to be safer to drink than raw milk which has not been pasteurized at all. The bulk of the milk sold in commercial grocery stores is pasteurized, and much of it is also homogenized to prevent the cream from separating.

The pasteurization process is named for Louis Pasteur, a noted French microbiologist. Pasteur made a number of notable discoveries in the field of microbiology, developing techniques which are still used today to reduce the risk of disease. In 1862, he performed early pasteurization tests, determined to render milk safe to drink, and the practice was adopted very quickly. Before pasteurization, improperly handled and stored milk caused widespread disease, especially in urban areas, where several unrefrigerated days might elapse between the cow and the end consumer.

There are several different pasteurization techniques which can be used to make pasteurized milk. The goal of pasteurization is to render the milk safe to drink without curdling or coagulating it, and without altering the flavor substantially, although people who are accustomed to drinking unpasteurized milk may find the pasteurized kind has an “off” flavor.

In high temperature/short time (HTST) pasteurization, the milk is brought to a temperature of 161 degrees Fahrenheit (71.7 degrees Celsius) and held there for 15 to 30 seconds before being rapidly cooled and packaged. Double pasteurization splits the process up into two segments, and is not recognized as a legal pasteurization method by some governments. Extended shelf life (ESL) milk is pasteurized at a slightly lower temperature and passed through a special filter to remove microbes. Ultra high temperature (UHT) pasteurization involves bringing the milk to 250 degrees Fahrenheit (138 degrees Celsius) for less than a second, while batch pasteurization is performed at a very low temperature, with the milk being held to temperature for 30 minutes before being cooled.

Even after pasteurization, milk is not totally stable. It will go bad within two to three weeks under refrigeration, with the exception of UHT milk, which can be held at room temperature in aseptic packaging for up to three months. Pasteurization also doesn't eliminate the risk of contamination along the supply line, as for instance in the case of pasteurized milk which is pumped through contaminated piping, and it doesn't eliminate heat-resistant organisms, although it does get rid of many common pathogens.

The benefit of pasteurization is that it renders milk much safer to drink. However, it also destroys some of the enzymes present in the milk, including enzymes which make milk easier to digest. It also alters the flavor of the milk, although people who are accustomed to milk that has been pasteurized may not be aware of the difference between fresh raw milk and pasteurized milk. As a result of these drawbacks, some people prefer raw milk, despite its dangers.

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Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a About Mechanics researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Discussion Comments
By anon161964 — On Mar 22, 2011

I wouldn't eat an uncooked food so same applies to milk.

By anon139219 — On Jan 04, 2011

the studies made on mice showed that pasteurized milk after two generations. They had no sex drive and they died.

By anon121754 — On Oct 25, 2010

I am not brave enough to drink pasteurized milk!

If raw milk comes from a healthy cow and is handled carefully, the incidence of food borne illness is much lower than that of pasteurized milk (or deli meat, for that matter).

Food borne illness is a risk we take every day (as is becoming more obvious- spinach, tomatoes, eggs, beef- more and more recalls from foods that are thought to be typically "safe"). Statistically speaking, if you drink unpasteurized milk from a farm certified to sell it in the US, you are 10 times less likely to get any sort of illness than if you consume deli meat from the supermarket.

It's a very fascinating topic. There are some great books out there on raw dairy, especially "The Untold Story of Milk."

By anon110418 — On Sep 11, 2010

I'm lactose intolerant and missed a good glass of milk. I tried Organic Valley Ultra Pasteurized milk and no "issues". The grocery store near us, New Seasons, is starting to replace the Organic Valley ultra pasteurized with pasteurized milk and my "issues" have reoccurred. Do not replace my milk!

By anon81989 — On May 04, 2010

My family grew up drinking raw milk from our own cows. We didn't boil the milk. The milk went straight from the cow to the refrigerator. We never got sick. I'm not sure I would trust raw milk from unfamiliar cows, but if the cow is healthy and the milk is handled safely, there shouldn't be any problem. And it does taste better.

By anon69709 — On Mar 09, 2010

I used to be lactose intolerant-- my parents gave me raw goat milk and I was healed within a month. Now I am 19 and drinking 1/2 gallon raw milk a day.

By bookworm — On Dec 03, 2008

I suppose if raw milk is brought to the boiling point than most of the bacteria would be killed. That is how milk was used before pasteurization.

I would not be brave enough to drink uncooked, unpasteurized milk. It is probably not wise to drink raw milk.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

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