How long will milk go bad? A complete guide to freshness

November 30, 2025 •

4 min read

According to the USDA, pasteurized milk can often be safely consumed for 5 to 7 days after its sell-by date if it remains unopened and is refrigerated below 40°F. However, several factors determine exactly how long will milk go bad after being opened or exposed to warmer temperatures.

Quick Summary

Milk spoilage depends on pasteurization, storage temperature, and exposure to bacteria. Freshness indicators include smell, texture, and taste, not just the printed date. Proper handling, like cold storage at the back of the fridge, can significantly extend its shelf life.

Key Points

Storage Temperature is Key: Keep milk at or below 40°F (4°C) on a back refrigerator shelf, not the door, to slow bacterial growth and extend freshness.
Dates Are Guidelines: The "sell-by" or "best by" date indicates peak quality, not absolute safety. Use your senses to determine if milk is spoiled.
Trust Your Senses: Obvious signs of spoilage include a sour or rancid smell, lumpy or curdled texture, and any visible discoloration or mold.
Proper Handling Prevents Contamination: Always seal containers tightly, and never pour unused milk back into the main carton to prevent cross-contamination.
Freezing Extends Shelf Life: Milk can be frozen for several months, but may require thorough mixing after thawing to address textural changes.
UHT vs. Pasteurized: Ultra-pasteurized milk has a much longer unopened shelf life than regular pasteurized milk due to higher heat treatment.

The Science of Milk Spoilage

Milk is a highly nutritious liquid, but this very richness is what makes it an ideal breeding ground for bacteria. Spoilage occurs when these microorganisms proliferate and break down milk's components, primarily its fats and proteins. This breakdown process, known as lipolysis and proteolysis, is what produces the off-flavors, sour smells, and curdled texture we associate with bad milk. While pasteurization kills most of the harmful bacteria, it doesn't eliminate all microbes. Some heat-resistant bacteria, known as psychrotrophs (like Pseudomonas), can survive the pasteurization process and continue to grow slowly in refrigerated conditions, eventually causing spoilage.

Factors Influencing How Long Will Milk Go Bad

Beyond the type of milk, several key factors dictate how quickly spoilage occurs. Understanding these can help you maximize your milk's longevity and reduce food waste.

The Role of Temperature

Temperature is the single most critical factor in preventing milk spoilage. Every time milk is left out at room temperature, even for a short period, it experiences a significant increase in bacterial growth. For instance, allowing milk to reach 50°F can effectively halve its shelf life compared to milk kept consistently at 40°F or below. Storing milk in the refrigerator door, where temperatures fluctuate with every opening, is a common mistake. Instead, store it on a back shelf, which is typically the coldest part of the fridge.

Handling and Cross-Contamination

Sealing: Leaving the milk container unsealed or drinking directly from the carton introduces new bacteria, mold, and yeast.
Unused Milk: Never pour leftover milk from a glass back into the container, as this will contaminate the fresh milk.
Cleanliness: A clean refrigerator and hygienic handling practices minimize the introduction of outside contaminants.

Packaging and Light Exposure

Milk is sensitive to light, which can degrade its nutrients and produce off-flavors through a process called oxidation. Opaque cartons and plastic jugs offer protection against light, which is why milk in glass bottles should be consumed more quickly.

How to Tell If Milk Has Gone Bad

Trusting your senses is the most reliable way to determine if milk is safe to consume, regardless of the date printed on the carton.

The Sniff Test: A strong, sour, or rancid smell is the most obvious sign of spoilage.
The Sight Test: Look for changes in texture and color. While fresh milk is a smooth, thin, white liquid, spoiled milk may appear chunky, lumpy, or yellowish. The presence of mold, which can appear as black or blue spots, is a clear sign to discard it immediately.
The Taste Test (with caution): If the smell and sight appear fine, take a very small sip. If it tastes sour or acidic, throw it out.

Comparison of Milk Shelf Life

The table below outlines the general shelf life for different types of milk, assuming proper refrigeration.


Milk Type	Unopened Shelf Life	Opened Shelf Life
Pasteurized (Regular) Milk	1-2 weeks after processing (lasts up to 7 days past sell-by date)	4-7 days after opening
Ultra-Pasteurized (UHT) Milk	6-9 months (shelf-stable before opening)	7-10 days after opening (refrigerated)
Raw Milk	5-7 days after collection	3-5 days after opening
Evaporated Milk (Canned)	6-12 months (pantry storage)	3-5 days after opening (refrigerated)
Powdered Milk	1-2 years (pantry storage)	1-2 weeks after reconstituting (refrigerated)
Plant-Based Milks (Almond, Oat, Soy)	Varies widely (UHT lasts longer)	7-10 days after opening (refrigerated)

Can I Freeze Milk to Extend its Life?

Yes, milk can be frozen to significantly extend its shelf life, which is an excellent way to reduce waste. For best results, freeze milk in a freezer-safe container or ice cube tray, leaving some room for expansion. Frozen milk can last for several months, though its quality may decline after prolonged freezing, leading to a grainy or separated texture upon thawing. To thaw, place it in the refrigerator for 24 hours. After thawing, use it within 3-5 days.

What About Using Spoiled Milk for Baking?

If milk is only slightly soured and hasn't developed a lumpy or moldy consistency, it can be used in some baking recipes that call for buttermilk. However, it is a riskier practice, and it is safest to throw out any milk that shows clear signs of spoilage. This practice should only be considered for baking at temperatures high enough to kill bacteria (165°F or above) and only if the milk is only slightly acidic. If the milk smells truly foul or is moldy, it is best to err on the side of caution and pour it down the drain.

Conclusion

Determining how long will milk go bad depends on a combination of factors, including the type of milk, proper storage, and handling. The printed date is a guideline for quality, not an absolute indicator of safety. By understanding the causes of spoilage, prioritizing consistent refrigeration, and relying on your senses, you can safely extend the usability of your milk and reduce food waste. When in doubt, the safest option is always to discard it. For more in-depth information on food safety standards, consult resources from the U.S. Department of Agriculture.

Frequently Asked Questions

It can be safe to drink pasteurized milk for several days past the sell-by date if it has been stored properly. Always check for a sour smell, unusual texture, and off-taste before consuming, as spoilage, not the date, is the primary indicator.

Drinking spoiled milk can cause digestive upset, such as nausea, vomiting, abdominal cramps, and diarrhea, due to the presence of harmful bacteria. A small accidental sip is usually harmless, but larger amounts can lead to food poisoning.

To maximize shelf life, store milk on a back shelf of your refrigerator where the temperature is most consistent and coldest, rather than in the door. Ensure the container is always tightly sealed to prevent contamination.

If milk is only slightly acidic and shows no signs of mold or thick curdling, it can be a substitute for buttermilk in certain baking recipes like pancakes or biscuits. Cooking at high heat will kill bacteria, but it's best to be cautious.

Unopened UHT milk can be stored at room temperature and last for 6 to 9 months. Once opened, however, it must be refrigerated and should be consumed within 7 to 10 days, similar to regular milk.

Milk should not be left unrefrigerated for more than two hours. If it has been sitting out for longer, harmful bacteria can grow rapidly, and it is safest to discard it.

Freezing milk is an effective way to preserve it for several months, though it may cause textural changes like separation or graininess upon thawing. It is still safe to use and can be stirred or blended to restore texture.