How long can unopened milk sit out? (3 categories of milk)

In this brief guide; we will answer the question, ‘ How long can unopened milk sit out?’. We will discuss the shelf-lives of store-bought milk that is raw, pasteurized or UHT treated. 

How long can unopened milk sit out?

Whether unopened milk can sit out depends on the background of milk. Milk is treated by either pasteurization or by UHT treatment. However, raw or fresh milk does not undergo any heat treatment. 

The Ultra High Temperature treated Milk will not go bad if left out overnight and can sit at room temperature for about 6 months. 

How long does unopen pasteurized milk last?

The pasteurization process kills bacteria by heating the milk at high temperatures. After potentially harmful microorganisms destroy, then it is aseptically sealed to ensure its longevity.  Once the seal has broken, pathogenic microorganisms cause the milk to spoil.

In Vat pasteurization, the milk is heated to only 161 Fahrenheit for 15 seconds. It is not as safe as UHT but better than raw milk.

However, it is not as secure and protected as UHT, therefore has to be refrigerated at all times. If you left it out overnight, there is an 80 percent that it has gone bad. If you had the same milk carton for a few days or a week, then your milk is likely to spoil overnight.

Pasteurized Milk lasts only four hours at room temperature. When other factors come into play, your pasteurized milk will last anywhere from three to six hours.

If Pasteurized Milk is left out overnight, it is likely to spoil. Pasteurized milk does not turn sour, it directly spoils. Pasteurized milk that was left out overnight could go bad or possibly not.

How long will unopened UHT-treated Milk last?

Milk treated to UHT lasts much longer than pasteurized milk and hence, is processed and sold at room temperature.

During Ultra-High Treatment of milk, it is heated at 280 Fahrenheits for only 2 seconds.

UHT-treated milk is shelf-stable and can sit out for a long time. 

Aseptic Milk, packaged after processing at an Ultra High Temperature, will last for six months if the seal was left intact. It can be left unopened and unrefrigerated not overnight but for months. 

However, an opened tetra pack will spoil if left out of the fridge.

How long can Fresh or Raw Milk sit out?

Fresh Milk, on the other hand, does not undergo any such process. Therefore you can expect it to have a shorter life, even if it has an intact seal.

Fresh milk, was not subjected to any kind of heat treatment which, owes to its short life. In an unopened milk carton, the seal has not broken yet. The intact cap does not allow entry to spoilage bacteria. However, the preexisting ones are responsible for spoilage. The milk bacteria, to name some are; Campylobacter, E Coli, Salmonella, and Listeria; all of these pathogens can make a person sick.

The bacteria that were present since the milking process; is delivered to you. Gradually, the bacteria already in milk, multiply and spoil the milk.

Other FAQs about Milk which you may be interested in.

How many gallons of milk can a cow produce?

How much milk can you drink?

How to Heat Milk in the Microwave?

What affects the shelf-life of milk?

If milk was not handled, processed, or shelved properly; the milk will have a shorter shelf-life. Even if it is unopened proper handling is important before and after packaging. 

Unopened milk can sit out for anywhere from a couple of hours to months.

If your raw, unpasteurized milk handling were not in alignment with the standard operating procedures, at the farm and after, its standard shelf-life would be shorter. 

Unopened Whole Milk lasts 5-7 days. Skimmed or reduced-fat will have slighter longer stability than unopened Whole Milk from 7-8 days.

However, the shelf-lives of milk that we discussed are conditional. They will be shorter if substandard handling occurred at;

  • the farm (cow health, milking protocols)
  • processing and transportation (sanitation and temperature control)
  • supplier handling (cold chain)

If the standard operating procedures have complied you can expect your milk to last around or after the expiration date.

However, if any of the safety procedures were compromised, you can expect milk to expire prematurely. The rules not only apply to unopened milk but opened milk as well. Hence, the better you treat your milk, the longer it lasts.

Fresh or Raw Milk could sour if it was left out all night, even if it was unopened. However, it is likely to occur depending on good farm handling practice; and how much further the milk is from the expiration date. 

After we have decided all the above factors, it now comes down to under what condition was the milk left out. If it was cold or at least room temperature and away from sunlight, your milk will possibly not turn sour.

In this brief guide we answered the question, ‘ How long can unopened milk sit out?’. We discussed the shelf-lives of store-bought milk that is raw, pasteurized or UHT treated. 



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