How should I store opened yeast?

The answer

Keep opened active dry yeast in an airtight container in the refrigerator or freezer, and use it within about 4 months. Red Star Yeast says opened jars must go in the refrigerator or freezer, with the freezer preferred, and be used within 4 months of opening. Unopened jars keep at room temperature away from heat. Write the opening date on the container, and open it briefly to limit moisture and condensation. If you are unsure, test the yeast in lukewarm water with a pinch of sugar.