Will milk go bad if left out overnight? 

In this brief guide, we will answer the question,’ Will Milk go bad if left out overnight?’ We will discuss the factors that make milk a perishable food and the appearance of signs that indicate spoilage.

Will milk go bad if left out overnight?

Yes, open milk lasts for about 2 hours before getting spoiled when left out at room temperature.

You should discard the milk that has been left in the open for more than 2 hours as bacterial growth takes place at a faster pace between the temperature of 40 and 140 degrees Fahrenheit.

Open milk, whether it be whole milk, skim milk, or reduced-fat milk, stays for about 4 to 7 days before getting spoiled when stored in the fridge at or below 40 degrees Fahrenheit in an air-tight container or bottle.

On the other hand, the unopened whole milk lasts for about 5-7 days,  reduced-fat and skim milk for 7 days while non-fat and lactose-free milk for 7-10 days past the printed date on it provided that it is stored properly in the fridge at or below 40 degrees Fahrenheit. (1-3)

How to store milk?

When it comes to storing pasteurized milk, it is recommended to keep it in the refrigerator at a temperature range of 3-4°C (38-40°F). Placing the milk carton in the refrigerator door should be avoided to minimize temperature fluctuations that can affect its quality.

If you wish to extend the shelf life of milk, freezing is an option. Frozen milk can remain safe for consumption for up to 6 months. 

However, for the best quality, it is advisable to consume frozen milk within a month. It’s worth noting that freezing may cause a slight grainy texture and fat separation in the milk. Therefore, frozen milk is better suited for cooking purposes or as an ingredient in smoothies and shakes.

To ensure proper storage, it is crucial to maintain the temperature of your refrigerator between 3-4°C (38-40°F). After using milk, promptly returning the carton to the refrigerator helps maintain its freshness and prevents potential spoilage. (4)

What factors affect milk shelf life?

The shelf life of milk is heavily influenced by storage temperatures and methods. 

Inadequate handling practices, improper storage temperatures, and insufficient storage durations can create opportunities for pathogenic microorganisms to enter, posing significant risks to public health.

In tropical regions where chilling facilities may be lacking during transportation, storage, or retail, bacteria cells can recover and proliferate due to favorable temperatures. 

Consequently, there is an increased risk of recontamination of processed milk even after heat treatment, primarily resulting from poor hygiene practices.

To mitigate these risks, it is crucial to implement proper temperature control and adopt suitable storage practices. By doing so, the growth of bacteria can be minimized, effectively extending the shelf life of milk and ensuring its safety for consumption. (5)

How does milk spoil?

Milk is home to bacteria such as lactococci and lactobacilli. At temperatures above room temperature, they breed and reproduce. The probiotic bacteria change the lactose milk sugar into its compositional units; glucose and galactose.

The formation of lactic acid starts, as proved by the familiar tangy smell and taste. As the casein develops, the curdling process starts. 

As milk deteriorates further, the bacteria take over the fats, which causes the occurrence of molds.

Spoilt raw milk may become inedible as it curdles and gains its distinct sour taste and odor.  However, it does not need to be discarded, as curdled milk is used to make cheese, cream, and kefir.

On the other hand, pasteurized milk does not become sour due to the absence of bacteria that cause the milk to curdle. Instead, it rots and becomes unfit for consumption. (6)

How to tell if that milk has gone bad?

As milk spoils, you can detect a rancid and sour smell. 

The texture and consistency change too, and the color becomes pale with a yellowish tinge. 

Other characteristics such as an “acidic aftertaste,” “chalky mouthfeel,” or “sourness” can serve as specific examples of milk spoilage. (6)

What happens if you drink spoiled milk?

If you drink milk that was left out overnight, you risk falling sick. Even if it smells and looks fine, it must be tossed out. 

Spoiled Milk can cause food poisoning with symptoms such as vomiting and diarrhea. 

It’s important to note that milk spoilage is caused by a wide range of microorganisms, but certain bacteria can pose significant health risks to consumers.

Fortunately, in most cases, these symptoms should significantly improve or disappear within three days. 

However, if the symptoms persist and worsen or if you have any concerns, it is advisable to seek medical attention and consult with a doctor. (6, 7)


In this brief guide, we answered the question,’ Will milk go bad if left out overnight?’ We discussed the factors that make the milk a perishable food and the appearance of signs that indicate spoilage.

Other FAQs about Milk which you may be interested in.

How long does breast milk last outside the fridge?

Can you freeze soy milk?


  1. U.S. Department of Agriculture. https://ask.usda.gov/ Website. Washington, DC. What is the “2 Hour Rule” with leaving food out?.
  2. Buehler, A. J., Martin, N. H., Boor, K. J., & Wiedmann, M.  Psychrotolerant spore-former growth characterization for the development of a dairy spoilage predictive model. Journal of Dairy Science, 101(8), 6964–6981. 2018.
  3. Lacroix, M., Bon, C., Bos, C., Léonil, J., Benamouzig, R., Luengo, C., … Gaudichon, C.  Ultra High Temperature Treatment, but Not Pasteurization, Affects the Postprandial Kinetics of Milk Proteins in Humans. The Journal of Nutrition, 138(12), 2342–2347. 2008.
  4. Adda Bjarnadottir, Kelli McGrane, How Long Is Milk Good for After the Expiration Date? Them. Healthline Media LLC. 2020
  5. Dortey, M. D., Aboagye, G., & Tuah, B.  Effect of storage methods and duration of storage on the bacteriological quality of processed liquid milk post-opening. Scientific African, 10, e00555. 2020.
  6. Lu, M., & Wang, N. S.  Spoilage of Milk and Dairy Products. The Microbiological Quality of Food, 151–178. 2017.
  7. Adda Bjarnadottir, Kelli McGrane, How Long Is Milk Good for After the Expiration Date? Them. Healthline Media LLC. 2020

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