How to Identify Spoiled Milk

Milk is rich in vitamins, minerals, protein, healthy fats, and carbohydrates. However, drinking spoiled milk can cause stomach discomfort. The expiration date on the packaging is a good indicator of whether the milk is still safe to consume, but there are many factors that can spoil milk before its expiration. By checking the smell, consistency, color, temperature, or performing a baking soda test, you can determine if the milk is spoiled.

Ensure the milk has been expired for no more than 7 days. If stored correctly, milk that has passed its expiration by no more than 7 days can still be safe to use. However, if it has expired and been kept at room temperature, it's highly likely that the milk has spoiled.

• The shelf life of milk depends on its fat and lactose content. Full-fat milk can still be used 5 days after expiration, while lactose-free or fat-free milk may last up to 10 days after expiration.
• If the milk has been expired for over a week, it's better to discard it, even if its color and smell seem normal.

Smell the milk to check for unusual odors. Smelling the milk is the first and most straightforward way to determine if it has spoiled. Fresh milk typically has no strong odor, while spoiled milk will have an unpleasant smell. If you need to quickly move the milk away from your nose, it’s likely spoiled.

• Even if the milk looks fine, if it has an unusual smell, it's best to avoid drinking it.
• If you’re unsure whether the milk has an unusual odor, ask someone else to smell it, or use another method to check and taste the milk to be certain.

Check the milk's consistency for curdling. Fresh milk is typically smooth and liquid. The consistency of milk depends on its fat content, with whole milk being thicker than skimmed milk. However, regardless of the type, you should always feel a smooth consistency when pouring it.

• Spoiled milk will curdle. You may need to stir the milk, as curdles can often form at the bottom of the container.
• You can also check inside the packaging. If you see any residue inside, the milk has gone bad.

Check if the milk has turned yellow or cloudy. Pour the milk into a clear glass and hold it up to the light. Fresh milk will appear clear, clean, and white. Spoiled milk tends to look cloudy or take on a yellowish tint.

• If you have trouble judging the milk's color, place a white piece of paper behind or beside the glass for comparison. Spoiled milk will have a faint yellow hue.

Determine if the milk has been stored at room temperature. Milk needs to be kept cold to maintain its quality. If left out at room temperature for a long period, it will spoil, even if the expiration date is far off. Milk left at room temperature for more than an hour is highly likely to be spoiled.

• If you live with family members or roommates, it can be hard to tell if the milk has been left out. Be sure to ask others to confirm.

Pour milk into a microwave-safe cup. If you’re still unsure about whether the milk is spoiled, try this method. Pour a small amount of milk into a clear glass cup about 2.5 cm high.

• Only pour a small amount to test; you can use the rest of the milk if it hasn’t gone bad.

Heat the milk in the microwave for 30-60 seconds. The time may be shorter if you use a larger microwave with higher power.

• If you’re not sure how long to heat the milk, start with 30 seconds. If the milk isn’t hot enough after that, heat it for another 30 seconds.

Discard any milk that has curdled or become sticky. Stir the warm milk and check if it remains liquid or starts to thicken. Milk that has gone bad will curdle or stick together after heating.

• Curdling occurs due to high acidity, causing the proteins in the milk to clump together.
• It’s normal for a thin layer of film to form on the surface of the milk when heated. This is not a sign of spoilage. However, the milk is still good if it remains liquid after you remove the film.

Place one teaspoon of baking soda (10 g) on a plate. You don’t need much baking soda to test the milk – just enough to observe the reaction. Make sure the baking soda is fresh; if it’s expired, the reaction may not be accurate.

• In general, avoid using expired baking soda for this test.

Drop a few drops of milk onto baking soda. You should use milk straight from the carton, not milk that has been heated. Just one or two drops is enough to observe the reaction with the baking soda.

Spoiled milk will cause the baking soda to bubble. Baking soda does not react with fresh milk. Spoiled milk, with a higher acidity, will react with the baking soda and release CO2 bubbles. The more bubbles that appear, the higher the acidity level of the milk. If no bubbles form, the milk is still safe to use.

• Even if the milk looks and smells fine, if bubbles form with the baking soda, it’s best not to drink it.

Store milk at temperatures below 4°C. Milk should always be kept in the refrigerator. If left at room temperature for long periods, it will spoil faster.

• Store milk in the main section of the fridge to ensure it stays cold. If placed in the door section, the milk will be exposed to temperature fluctuations every time the fridge door is opened, reducing its shelf life.

Avoid exposing milk to light. Milk stored in clear glass or plastic containers won't last as long as milk in cartons or opaque plastic containers. Light exposure will cause milk to spoil, even if it’s just briefly when you open and close the fridge door.

• If you store milk in a transparent container, place it deep inside the fridge and cover it with other foods to reduce light exposure.

Secure the milk carton lid tightly. Fresh milk exposed to air can spoil even if stored properly. Always ensure the lid is tightly closed after use, and it’s best to keep the milk in its original packaging as it is designed specifically for milk storage.

• If the original carton is damaged, transfer the milk to a bottle or jar with a secure lid. Avoid storing milk in an uncovered jar or cup, even in the fridge, and write the expiration date on the new container.
• If the lid is loose, you can wrap a piece of plastic or wax paper around it to ensure it’s sealed as tightly as possible.

A final option is to freeze the milk. You can store milk for up to 3 months in the freezer. If you live alone and don’t drink milk often, this is an economical way to prevent milk from going to waste.

• When thawing, you can place the milk in the fridge or immerse the bottle/carton in cold water.
• Freezing may alter the texture and color of the milk slightly. It may even resemble spoiled milk in consistency and color, but it is still safe to use. The taste might not be as fresh as usual.