Yogurt is a fermented product, made by inoculating dairy with beneficial bacteria, so it's hard to tell when your tub or container is past its prime. Contrary to popular belief, fermented foods can indeed go bad, and here are signs to look for if you suspect your yogurt has gone off.

Biologists at Yogurt Nerd explain that excess water in your yogurt container can indicate spoilage. However, this fluid can be mistaken for whey, a dairy byproduct that often forms on top of yogurt; the key difference is that whey is always clear, so if the fluid in your yogurt looks cloudy, toss it out.

Another way to check your yogurt's freshness is to simply look at the expiration date. These dates aren't always foolproof indicators, but they are a good frame of reference; according to Eat By Date, unopened yogurt has a shelf life of two to three weeks in the refrigerator, or one to two months in the freezer.

Also, yogurt that's been opened already lasts for much less time: roughly one week in the fridge or less than a month in the freezer. Expired yogurt may also exhibit signs of spoilage such as a rancid, unappetizing smell, visible mold growth in the contents, or a bloated container, caused by the release of gasses.