I just bought this pack of ground beef from the store yesterday and put it in the fridge. I went to cook dinner and noticed the plastic film is puffed up like a balloon, but the date is still good. Wh

What Causes the Plastic to Puff Up?
When the plastic film on a package of ground beef becomes inflated, it usually means one thing:

Gas has built up inside the package.

And that gas doesn’t appear out of nowhere.

In most cases, gas buildup is caused by microbial activity — meaning bacteria inside the meat are multiplying and producing gases as they break down proteins and nutrients.

This can happen even if:

The “sell by” or “use by” date hasn’t passed.

The meat was only purchased a day or two ago.

The beef still looks red on the surface.

The key takeaway: a puffed-up package is a warning sign.

Why Bacteria Produce Gas
Raw meat naturally contains bacteria. Even fresh beef is not sterile. When meat is processed and ground, the surface bacteria are mixed throughout the product, increasing the risk of spoilage.

As bacteria multiply, they:

Consume nutrients in the meat

Break down proteins

Release gases such as carbon dioxide and other byproducts

If the package is sealed tightly — as most supermarket trays are — those gases have nowhere to go. So the plastic expands outward like a balloon.

This is very different from normal packaging tension. A truly swollen package will feel tight and rounded rather than flat.