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The shelf life of milk
My family drinks about 6 gallons of milk every week. While my husband and sons prefer plain white milk, I drink chocolate milk. I was at the milk case picking out my chocolate milk when I noticed the two brands I usually choose from had very different expiration dates. That got me wondering why there was a difference in shelf life.
It turns out there are different types of pasteurization, and the two brands I buy use different ones. Pasteurization is the process of heating raw milk to a minimum of 145°F. for 30 minutes followed by rapid cooling. The process was first used in the 1800s to preserve wine and is now used to destroy bacteria in many foods, including milk.
A standard gallon of milk has a shelf life of 19 days and is pasteurized using the HTST method. This uses a high temperature over a short time to pasteurize milk. The legal minimum is 161°F. for 15 seconds.
Milk can also be pasteurized using the extended shelf life, or ESL, method. Also called ultra-pasteurized, this method heats milk to 190°F. to 195°F. for 10 to 15 seconds. ESL milk will have between 30 to 90 days of shelf life.
Looking through the milk case I noticed several brands, including certified organic milk, had a longer shelf life. I had an opportunity to tour a milk processor and asked them why there were different methods.
They explained that ESL pasteurization was originally used for organic milk. There are fewer certified organic dairies and processors. That milk must travel farther from the farm to the processor to the grocery shelf, so it needs a longer shelf life. It lasts longer because of the ESL pasteurization process, not because of the milk itself. That process can be used to pasteurize any milk, not just organic.
According to The Dairy Alliance, pasteurization does not significantly affect the nutritional value of milk or change the taste of milk. You can look on the milk carton to see if the type of pasteurization used in identified.
The differences in pasteurization give me more options at the dairy case and let me buy enough milk to last the month.