How to test baking powder or soda?

Read this important tip somewhere!
Both baking powder and baking soda can lose their potency over time. So here's a tip to test them for freshness.

Baking powder:

Place a few tablespoons warn water in a small bowl. Add a teaspoon of baking powder. It should fizz and bubble - the more bubbles the better.

Baking soda:

Instead of water, use white vinegar. The baking soda should bubble up and foam.

Hope this helps!