How to Store Yeast
Buy yeast in an amount you will use within several months. Once opened, yeast should be placed in an airtight container in the fridge or freezer. In the freezer, yeast can survive for a year or more. If you are unsure of your yeast, the safest option is to replace it. You can try to proof your yeast to test it, but it can be hard to tell just how active it still is.