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How Long Does it Take for Milk to Spoil? Read This!  

Milk should be stored at about 45°F, but not less than 32 degrees.

If the temperature fluctuates too much, the milk will spoil faster.

Rapid and continuous temperature changes can cause the growth of bacteria like lactobacilli and lactococci.

These bacteria convert lactose to galactose and glucose, which produces lactic acid and spoils milk.

Lactic acid produces casein, which curdles milk in 24 hours.

If milk starts to curdle towards the lower part of its container, it is deemed spoilt and should be immediately thrown away.

Because bacteria grow on milk’s buttery fat, the mold grows too, and the milk spoils more.

How long does it take for milk to spoil?

According to the FDA, unrefrigerated milk starts to spoil after two hours at 39°F. As the ambient temperature rises, milk starts to spoil even quicker. By the time the ambient temperature is higher than 90°F, milk starts to spoil in just one hour.

How Long Does it Take for Milk to Spoil?
How Long Does it Take for Milk to Spoil?

What is meant by ‘milk spoils’?

Spoiled milk

Spoiled milk results from an increase in bacteria that alters milk’s texture, quality, and flavor.

The most dangerous strains of organisms that can cause illnesses include Salmonella, E. coli, and Listeria.

Over time, small colonies of these bacteria multiply and eventually destroy the milk completely.

As the milk begins to deteriorate, it will develop an unpleasant, rancid odor. The smell is hard to ignore and becomes more intense over time.

The taste starts to change too since the sweetness inherent in fresh milk is soon substituted by a slightly acidic or sour flavor.

As time passes, the texture, color, and appearance of the milk change dramatically.

Spoiled milk will look chunky, slimy, and dull yellow.

The increase in bacteria is what spoils milk
The increase in bacteria is what spoils milk

Curdled milk

Fresh milk illustrates colloids, which are composed of protein and fat particles floating in a solution of water.

It is acidic if the pH drops in milk and dairy proteins like casein and others bind, forming curdles or lumps.

These lumps grow faster at higher temperatures.

When milk has begun to curdle, it is considered spoiled.

However, foods that people love and eat in plentiful amounts depend on curdled milk. Such foods are buttermilk, yogurt, and cheese.

Milk also curdles when it is cooked for too long, or on heat that is too high, due to the evaporation of water in the milk.

Since milk that has curdled like this is due to heating and not to the action of bacteria on its pH level, such milk is perfectly okay to drink.

In fact, it is possible to reconstitute the milk by whisking in some cornflour and water.

Unrefrigerated milk starts to spoil after two hours at 39°F
Unrefrigerated milk starts to spoil after two hours at 39°F

Spoiled milk vs. sour milk

The terms sour and spoiled are frequently used interchangeably to refer to the condition of milk that has gone bad.

However, there could be subtle distinctions between the two depending on the person you ask.

Spoiled milk typically refers to pasteurized milk that has a distinct smell and tastes off due to the development of bacteria that have survived the process of pasteurization.

This type of bacteria is harmful and can make you sick.

Sour milk often means raw, unpasteurized milk that has started naturally fermenting. Like spoiled milk, the process of fermenting raw milk is caused by diverse lactic acid-forming bacteria.

Scientists deem a tiny proportion of these bacteria probiotics and think they offer slight health benefits.

The advantages of raw milk do not outweigh the potential dangers.

It’s generally inadvisable to drink unprocessed milk–fresh or sour–because of the potential threat of food poisoning.

Milk should be stored at about 45°F, but not less than 32 degrees
Milk should be stored at about 45°F, but not less than 32 degrees

‘Going off’ milk vs. ‘gone off’ milk

While you shouldn’t drink spoilt milk, it’s still far from useless.

If your milk is extremely old and is beginning to curdle, get slimy, or even grow mold, then just get rid of it.

However, if it’s only a bit off and only slightly acidic, there are various methods to make use of it.

Try using milk that is slightly spoiled in one of these recipes:

  • Baked goods. Replace regular milk in sour cream, yogurt, and buttermilk, in recipes such as cornbread, scones, biscuits, and pancakes with spoiled milk.
  • Cheesemaking. Produce cottage cheese or farmer’s cheese using sour milk.
  • Salad dressing. Use spoiled milk to create creamy dressings such as ranch, Caesar, or blue cheese.
  • Soups and stews. A splash of spoiled milk can assist in thickening and adding flavor to stews, soups, and casseroles.
  • Tenderize. Make use of sour milk to marinate and soften meat or fish. It is also possible to soak uncooked whole grains to help them soften.

Pasteurization and the prevention of milk spoilage

Pasteurization is a method for preserving food products using heat, generally at a temperature below 212°F over a specific duration.

Its goal is to lower the number of viable pathogens that cause spoilage to extend the shelf life of milk without compromising its quality.

There are four kinds of milk pasteurization which differ on temperature and duration of time milk is kept at that temperature.

  • Low Temperature/Short Time (HTST) where milk is heated to 162°F for 15s.
  • Ultra-High-Temperature (UHT) maintains milk for 2s at 280°F.
  • Ultra-pasteurization (UP) is heating milk from 280°F to 302°F for 1-2s.
  • Vat Pasteurization/Low temperature/Long-time pasteurization, where milk is heated to 145°F for 30m.

Pasteurization’s goals are:

  • To kill the harmful microorganisms found in milk and dairy products.
  • To guarantee a high quality of milk and milk products.

How to store milk to prevent spoilage

Milk is susceptible to air and light exposure. It should be kept in a cool place far from direct sunlight. Milk should be kept refrigerated for at least 24 hours of opening.

The refrigerator helps to keep milk from spoiling and prolongs the shelf time.

Don’t keep dairy products in containers made of plastic. Plastic containers let oxygen into the milk, which can encourage bacterial growth.

Store milk in glass bottles or other kinds of containers made from glass.

Glass allows milk to breathe and keeps bacteria from expanding. Never freeze milk. It can damage the protein structure and alter its taste.

Frequently Asked Questions About How Long Does it Take for Milk to Spoil

Is it okay to freeze milk?

It depends on what is meant by ‘okay.’ Bacteria won’t grow in frozen milk, but thawed milk can separate as its water thaws quicker than its fats, leaving an unsightly, making for an icky, weird-tasting mess.

How can I store milk without refrigeration?

The milk can be kept indefinitely without refrigeration, simply by boiling it regularly between 6-8 hours. The milk will thicken after 3-4 boiling sessions. You might add boiling water to alter the thickness before boiling again.

Afterword: How long does it take for milk to spoil?

Spoiled milk isn’t just ugly, but also dangerous because it will contain dangerous bacteria that might lead to serious illnesses such as fever, abdominal cramps, vomiting, diarrhea, even death.

According to the FDA, unrefrigerated milk starts to spoil in as little as an hour. Refrigerated milk will keep for about seven days.

Detect spoiled milk by smelling it (it will smell foul) or tasting it (it will taste bitter or sour).