Yes. Moist kitchen air - which enters the baking powder canister each time you open it - dramatically lowers a baking powder's potency. As the below experiment demonstrates. Always test your baking powder's potency before using it by mixing a little of it into a little water. The fresher the baking powder, the more actively this mixture will bubble. If the chemical reaction is weak or does not occur, your baking powder will not properly raise whatever you are planning to bake.

Baking Powder Potency Experiment
Setup two 8-ounce measuring cups (or glass bowls). Call them A and B. Open a new can of baking powder. Transfer 1 teaspoon of it into cup A. Promptly close the can. Then cover cup A with several layers of very damp paper toweling (it should not touch the powder). Six hours later reopen the can and transfer 1 teaspoon of its powder into cup B. Into each cup, stir in a half-cup of cold tap water. Which produces the most bubbles and, therefore, is more potent?

** Asian Recipes **