Testing Baking Powder and Soda
If you don't seem to have much success with making baked goods, there may be a simple answer—your baking powder and/or baking soda may not be fresh. The shelf life for these products is about 6 months, but here's how to test for freshness to be sure:
For baking powder, place 1 teaspoon baking powder in a cup and add 1/3 cup hot tap water.
For baking soda, place 1/4 teaspoon baking soda in a cup and add 2 teaspoons vinegar.
If active bubbling occurs, the products are fine to use. If not, they should be replaced. When buying a new can, check for an expiration date.