Yeast is a natural product and spoils just like other foods. How long you can still use expired yeast, you can find out here.
When you should dispose of expired yeast
First, we need to distinguish between fresh and dry yeast: Dry yeast has a much longer shelf life than fresh yeast. For dry yeast, you can use the best-before date as a guide. If the yeast is past the best-before date, then you can still use the yeast relatively safely for a few days. Fresh yeast also has a best-before date. However, this is shorter, usually the yeast can be kept for 10 to 14 days. Even beyond that, you can still use yeast for a few days if it has been stored in a cool place.
Check food before use
There are signs when fresh yeast is no longer edible. Fresh yeast is soft, and uniformly light gray to light brown. If it is dark, spotty or dry, you should not use it. A smeary film on the food or a vinegar-like odor also indicates that the yeast has spoiled. There is a trick to finding out if the yeast is still usable. Place the yeast in a glass of water. If it floats to the top, you can still use it as long as it does not otherwise show any of the aforementioned signs.
