Is It Safe To Drink Milk in a Bloated Container?

I can’t start my day without a big bowl of cereal drowned in milk. When I’m choosing the perfect half gallon of 2% at the grocery store, I’ve seen milk cartons that look a little bloated, like someone overinflated a balloon. Are these swollen containers of milk safe to consume?

It depends on what’s causing it, says microbiologist Jason Tetro, host of the Super Awesome Science Show and author of The Germ Code and The Germ Files. “Bloating can occur due to air pressure changes or microbial growth,” Tetro says. “Usually air pressure is gentle bloating and reversible whereas microbial growth is hard bloating and irreversible.”

Bloating caused by changes in air pressure happens because of altitude and temperature shifts, says Tetro, while microbial growth is a natural process and occurs in refrigerated milk.

The Science of Why Milk Containers Bloat

“The bloating of milk cartons is caused by gas production (such as carbon dioxide), due to microbial action on lactose (milk sugar),” explains Pranav Vashisht, continuous improvement specialist at Idaho Milk Products Inc. and member of the Institute of Food Technologists’s dairy foods division.

Some of the causes of bloating—also known as “bulging defect” or “abnormal fermentation”—include improper processing of milk or sanitization of cartons. It can also happen if packages are defective and allow air to enter containers, encouraging bacteria to grow.

Is Milk From a Bloated Container Safe To Drink?

Milk safety in a bloated carton depends on if it is due to air pressure or microbes. If you’re in a high-altitude place and you’re not close to the best-before date, milk should be fine to drink. Otherwise, it’s best to pass over a bloated milk carton.

“Consuming such milk is unsafe due to the high levels of bacterial growth, which can pose health risks,” says Vashisht. “Drinking this milk can lead to gastrointestinal issues such as nausea, diarrhea, abdominal pain, and vomiting, and in some cases, the effects could be even more severe.”

How To Check If the Milk Is Safe To Drink

To check milk safety, Tetro suggests first shaking the carton to see if anything has solidified and formed chunks. Next, put it in the fridge to see if the bloating lessens. If so, you know it’s likely due to air pressure. If the container stays bloated, it’s best to ditch it.

Vashisht also recommends checking for any visual defects like gas bubbles, flakes on the sides of the carton, curdling, or anything that settles in the bottom of the container.

And never underestimate the power of the smell test. “Bacteria that ferment lactose into lactic acid and gas often produce a tingling odor,” explains Vashisht. “You can take a small sip and give the milk a little twirl in your mouth with the help of your tongue, it will cover your taste buds with the product and then sense for any off flavor.”

Tetro suggests putting some milk into a glass for a good sniff test. “Just put it into a glass rather than smell the opening of the carton,” Tetro suggests. “If anything is a positive, best to throw it out or maybe think about making some homemade yogurt.”

Finally, check the best-by or use-by date. “Even after proper processing milk quality degrades day by day,” says Vashisht. “It is susceptible to microbial contamination with minimal exposure to unfavorable conditions. If you have milk from two different lots in your refrigerator, always use the one with the earlier best-by date first.”