Shelf Life of Yeast

• An unopened package of dry yeast, whether in bulk, small jars or individual packets, will last up to four months in the pantry, or until the expiration date marked on the package -- typically, whichever is longest. An opened container of yeast will last about the same amount of time, but store it in the refrigerator. To extend the life of your yeast even further, store it in an airtight container in the freezer; properly stored yeast will a year or more in the freezer.

Testing Yeast

• Regardless of how long you've had the yeast, it's a good idea to check whether it's still alive before you incorporate it into your recipe -- this process is often referred to as "proofing." In a one-cup liquid measuring cup, dissolve 1 teaspoon of sugar into 1/2 cup of warm tap water and stir in 2 1/4 teaspoons of yeast; after 10 minutes, the mixture should have bubbled up to the 1 cup mark. If the yeast falls short of this mark, it has little to no activity and should be discarded.

Storing Bulk Yeast

• If you buy yeast in bulk, consider decanting it into smaller containers to minimize waste. Glass or acrylic airtight containers, including mason jars, work well for this purpose; simply divide the bulk yeast into three or four containers and store them in the freezer to maximize the yeast's shelf life. When you need some, measure out the amount needed -- 2 1/4 teaspoons equal one packet -- and put the rest back in the freezer. There is no need to allow the yeast to come to room temperature before proofing.

Active Dry vs. Instant Yeast

• Both active dry and instant yeast should be stored using these same guidelines. They are almost completely interchangeable in recipes, one-to-one, with the exception of bread machine recipes which do better with active dry rather than instant yeast. Active dry yeast might take longer to rise than instant yeast, but this is not a sign that the active dry yeast is old or inactive; be flexible with the rising time for recipes in which you've used active dry yeast, and proceed once the dough has risen to the desired level.