How Long Can Milk Stay Unrefrigerated?

From the Cow to the Grocery Store

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  Milk begins its journey straight from the cow at a temperature of about 100 degrees Fahrenheit. It is then kept cool in preparation for the pasteurization process, in which it is heated to a temperature of 145 degrees for a short time, then quickly cooled to about 38 degrees. From that point on, milk is kept chilled at that same temperature during packaging and then transportation to grocery store shelves. The entire process takes about two days from udder to store. Each container of milk has been stamped with a "sell by" or "use by" date. Generally, milk is still good for two or three days after the sell-by date.
  
  

Refrigeration Needs of Milk at Home

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  According to the National Dairy Council, milk needs to be refrigerated and stored at a temperature between 35 and 40 degrees. Food, including dairy products, that reach temperatures between 41 and 140 degrees (the "danger zone") are potential breeding grounds for salmonella and other coliform bacteria. The general rule of thumb is that milk can stay unrefrigerated for about two hours, but then must be refrigerated as soon as possible after that. In summer, food spoils faster, so it's even more critical to follow the two-hour guideline. If the milk container is still somewhat cool to the touch, it's probably okay.
  
  

Is It Spoiled?

• Milk that has been exposed to strong light, left out on a counter for more than two hours or frozen and then thawed can develop off-flavors. The Wisconsin Dairy Council states that for every 5 degrees over the ideal 40-degree refrigeration temperature for milk, its shelf-life is shortened 50 percent and it quickly loses its pleasant, fresh taste. Containers that appear bloated or swollen, milk with a sour or acidic taste and certainly any milk that appears to have separated or coagulated are all definite signs that milk has gone bad and should be tossed immediately. All milk will spoil eventually, but exposing it to warm temperatures accelerates bacterial growth.
  
  

Drinking Spoiled Milk

• Drinking milk that has been left on a counter at room temperature for several hours may or may not make you sick, but drinking potentially bacterial-laden milk isn't worth the gamble. Campylobacter, a bacteria present in spoiled milk, can cause diarrhea, fever, cramping, vomiting and headaches. When in doubt, pitch any warm milk that's been sitting out on the counter, and make sure baby bottles and toddler "sippy cups" are emptied and cleaned as soon the child is finished with them, or refrigerate any unused portions right away.
  
  

Soy, Raw Milk and Shelf-Stable Milk

• As soon as any milk product is opened, whether it's a box of shelf-stable milk, a can of condensed milk, a container of soy milk, or unpasteurized raw milk, the two-hour rule for leaving it unrefrigerated goes into effect. Even though shelf-stable milk can last on the pantry shelf for several months, when it is opened, it is prone to the same bacteria that affects whole or lower-fat milk.