Why Milk Spoils and How to Extend Its Shelf Life: Tips

Different types of milk can stay fresh for different periods of time. Milk can be safely consumed for several days after the expiration date. The shelf life of food and beverages depends on their quality, not their safety.

Drinking spoiled milk can make people feel sick, but it is usually easy to tell when milk is bad. There are many types of expiration dates for food and beverages, which can be confusing. Milk producers usually pasteurize milk before selling it to kill bacteria. However, milk can still spoil and become unsafe to consume.

In this article, we will discuss how long milk can remain safe after the expiration date and explain what different dates on food and beverage labels mean.

Preservation after the expiration date

There is no universal length of time that milk can be safely consumed after the expiration date. Different types of milk can stay fresh for different periods of time.

Most milk has been pasteurized, which involves heating the milk to kill harmful pathogens. While this makes milk safer to consume, it does not mean that it is safe to store milk out of the refrigerator for long periods of time, especially after it has been opened.

Some evidence suggests that pasteurized milk should remain fresh for 2-5 days after the use-by date and 10-21 days in total.

There are different pasteurization methods that can further extend the shelf life of milk. For example, ultra-pasteurized milk can be stored for about 30-90 days. This longer shelf life is due to the higher heating temperature during processing.

Producers produce aseptic milk, or ultra-high temperature milk (UHT), by heating the milk using sterile equipment and bottling it under aseptic conditions in specially designed containers that can extend the shelf life to more than 6 months. The product itself can also be stable in storage, meaning that it does not require refrigeration until a person opens it.

It is recommended to avoid consuming raw or unpasteurized milk, as it may contain harmful pathogens that can pose a serious health risk.

Why does milk spoil?

Milk naturally contains bacteria that can spoil and cause illness, such as E. coli and Salmonella. Milk spoilage is the result of an overgrowth of bacteria that impairs the texture, taste, and overall quality of milk. Psychrotrophic bacteria, which can grow in cold conditions, are often the cause of milk spoilage.

Milk production involves several steps to kill these bacteria to extend the shelf life. Milk processing includes:

  • Pasteurization: producers heat the milk to kill bacteria before cooling it again.
  • Homogenization: A sprayer distributes the fat evenly throughout the milk and prevents it from floating to the top.
  • Separation: A centrifuge spins the milk to separate the cream before combining it with different amounts of fat for different types of milk. Several other steps may also be required, including additional filtration or ultra-high temperature treatment.

Pasteurization kills most, but not all, of the bacteria in milk, which can continue to grow after processing. When you open milk at home, new bacteria can get into it and multiply, which will eventually lead to milk spoilage.

How to know if milk is bad

The expiration date is a poor indicator of whether milk is safe to consume. The smell and appearance of the milk are clearer indicators of how safe it is to consume.

Spoiled milk will have a sour odor as bacteria produce lactic acid. The odor intensifies when the milk becomes unsafe to drink. A yellowish color, crusts around the edges, and lumps in the milk also indicate that it has spoiled.

Ways to extend the shelf life of milk

The processing of milk has a significant impact on how long it stays fresh and safe to drink. However, there are steps people can take at home to extend this period. This includes:

  • putting milk in the refrigerator as soon as possible
  • tightly close the lid on the milk after use
  • Keep hot foods away from milk in the refrigerator
  • do not leave milk in the refrigerator for long periods of time
  • keep the refrigerator temperature below 4 degrees

Side effects of drinking spoiled milk

Consuming small amounts of tainted milk may not cause any symptoms or may cause some minor symptoms that usually go away on their own. For example, it may cause abdominal pain, nausea, diarrhea, or vomiting. Spoiled milk is unlikely to cause long-term problems.

However, drinking raw unpasteurized milk is dangerous. Raw milk contains harmful pathogens that cause food poisoning, including:

  • Campylobacter
  • Cryptosporidium
  • Escherichia coli
  • Listeria
  • Salmonella
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Written by Emma Miller

I am a registered dietitian nutritionist and own a private nutrition practice, where I provide one-on-one nutritional counseling to patients. I specialize in chronic disease prevention/ management, vegan/ vegetarian nutrition, pre-natal/ postpartum nutrition, wellness coaching, medical nutrition therapy, and weight management.

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