How do I know if my baking powder is still fresh?

[True2marie]

I can't find the expiration information on a container of baking powder in my kitchen cabinet. I know I have had it for a while, but I don't if it's stale or not. How do I tell if my baking powder is still fresh?

 

[MyDigitalpoint]

I found myself in such dilemma with some baking power cans in my pantry, but thinking that it should be okay based on the fact that they were bought more or less by the same time and the expiration date in the others showed one more month of useful life, I took this can with the expiration information, added a tablespoon to the wheat flour an hot water as the recipe called, but the mix didn't bubble up.

Add hot water to a tablespoon of baking powder and see; bubbles are the way to tell if it's still fresh.