First things first: check the expiration date. The shelf life for an open container of baking soda or baking powder is about 6 months, but here’s how to test for freshness to be sure:
How to Do a Baking Powder Test
Place 1 teaspoon baking powder in a cup and add 1/3 cup hot tap water. If it starts to bubble, it’s good to go. If not, add it to your grocery list.
How to Do a Baking Soda Test
Place 1/4 teaspoon baking soda in a cup and add 2 teaspoons vinegar. Just like baking powder, if baking soda doesn’t bubble, it’s old and should be replaced. If you’re left without baking soda or baking powder, here’s how to make cookies without.