How long can unopened milk sit out?

In this brief guide, we’ll address the search query: “How long can unopened milk sit out?” Also, we’ll explore how milk should be stored, how our readers can tell if their milk has spoiled, and what are the risks of drinking spoiled milk

How long can unopened milk sit out? 

This will depend on what the milk’s storage requirements are. For reference, a milk carton that has been purchased from the refrigerated food section can stay out at room temperature for roughly two hours before it begins to spoil.

However, some dairy companies make ultrapasteurized milk, which is much more shelf stable and can keep for days, and sometimes even weeks before it is opened, at which point, it will require refrigeration.

We encourage our readers to carefully review the instructions that come with their perishable food products so that they can decide what option and storage best suits their needs. 

How should milk be stored? 

Ideally, milk should be stored in refrigeration, especially once it has been opened. This is because opening a carton of milk exposes it to airborne microbes, such as molds and bacteria, which can hasten the spoilage of dairy products. 

Due to its liquid state and ergo, the moisture present in milk, it is especially susceptible to the effects of microorganisms. Its sugar content (in the form of lactose) may favor the growth of microbes and its fat content makes it susceptible to souring, as these fatty acids may break down and turn rancid. 

Ultrapasteurized milk and powdered milk are among the more shelf-stable variations of this product, though once opened, the latter should be stored in refrigeration. 

Powdered milk can be stored on a cool, dry shelf, within a tight sealing container where no moisture will seep in, and no critters will find the powder. 

In some cases, such as if our readers have purchased regularly pasteurized milk in bulk, it may be feasible to store it at subzero temperatures. However, if the milk has a modest concentration of dairy fat, it may be unpalatable after a round of freezing and defrosting, as this can cause the fat to separate and clump. 

Freezing may be feasible if the milk will be used in cooking, and its texture is of little to no importance for downstream applications. 

How can I tell if milk has spoiled? 

Our readers can tell if their milk has spoiled by observing for any of the following signs: 

  • An offensive, or off-putting smell
  • Discoloration – a greenish-yellow color
  • A bitter taste – a result of chemical processes driven by oxidation, which may or may not involve microorganisms.
  • A change in consistency, such a curdling. Curdling separates casein from whey, and when this occurs, the milk may give off an unpleasant smell if kept at room temperature. 

We encourage our readers to be mindful of the storage conditions in which they keep their milk and other perishable products. Also, milk should be consistently stored at low temperatures to keep its components from spoiling, and to avoid favoring the growth of microbes within it. 

What are the risks of drinking spoiled milk? 

Drinking spoiled milk can be hazardous to our readers’ health. Namely, if there are bacteria and mold present, these microorganisms can trigger symptoms of food poisoning. 

Symptoms may include abdominal pain, fever, nausea, vomiting, diarrhea, dehydration, muscle aches, headaches, and other associated symptoms.

Individuals at heightened risk of food poisoning include the elderly, pregnant women, young children, and patients with compromised immune function. 

Severe symptoms such as dehydration may require hospitalization and administering electrolytes intravenously, as well as a course of antibiotics to address the infection. 

We urge our readers to prioritize their health and be mindful of the storage conditions that they store their food and perishable products in, and to discard food that shows any signs of concern or spoilage. 


In this brief guide, we’ve addressed the search query: “How long can unopened milk sit out?” Also, we’ve explored how milk should be stored, how our readers can tell if their milk has spoiled, and what are the risks of drinking spoiled milk


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