It's packed with protein, comes in dozens of flavors and can be eaten on the go, so what's not to like about yogurt? It's a delicious dietary staple until you get a spoonful of spoiled yogurt and swear it off forever. Luckily, there's not too much mystery involved in identifying yogurt that's gone bad. Spoiled yogurt is pretty easy to spot by sight and smell alone.
Yogurt and Expiration Dates
Like all dairy products, yogurt has a limited shelf life. It will last considerably longer than milk, but a carton of yogurt generally won't keep for longer than three weeks before turning sour. It will turn bad long before that if it's exposed to air, especially if any saliva has been introduced into the yogurt. Once a container of yogurt has been opened, it should be eaten within a few days.
That said, the carton's expiration date isn't necessarily an indication of whether yogurt is safe to eat. The United States Department of Agriculture's official position is that yogurt can be kept in the refrigerator for up to two weeks, but that doesn't take into account how old the yogurt is when you buy it. Although the expiration date will provide some context, it's not an absolute ruling of when yogurt becomes unsafe to eat. Because yogurt can be edible for a week or longer past its expiration date, visual cues are the best indicators of spoiled yogurt.
The expiration date is still helpful to note, so be mindful of that when you buy yogurt in a multipack. Check whether the cartons have individual expiration dates. If the expiration date is only on the external packaging, mark the date on each cup so you don't lose track.
Identifying Spoiled Yogurt
There are a few key indicators that will tell you that your cup of yogurt has passed its prime. One is excess liquid. It's normal for yogurt to have some liquid on the surface, especially Greek yogurt, but spoiled yogurt will often have a puddle of liquid on top. It may be clear or whitish, but either way, it's a bad sign.
A change in texture may also occur in spoiled yogurt. If you stir the yogurt with a spoon and notice that its texture looks grainy, unusually thick or curdled, it should be tossed. Spoiled yogurt may also have a sour smell or even visible mold of any color, which are both obvious indications that it shouldn't be eaten.
Be especially diligent about checking for mold if you favor yogurt flavors that have fruit on the bottom or fruit in an attached container. Because fruit can develop mold quicker than yogurt, these varieties should ideally be eaten by their expiration dates.
How to Freeze Yogurt
If you find that your yogurt is often turning bad before you get around to eating it, it might make sense to stash those containers in the freezer to extend their window of edibility. Yogurt can be frozen for up to two months per the USDA. Thaw a container in the fridge overnight or for a few hours at room temperature. This strategy will prevent mold, but be warned: Like with other dairy products, freezing and thawing yogurt may cause it to separate somewhat.