I learned the hard way that baking powder doesn’t last forever. When I had my bakery, I ordered a gigantic can of the stuff. It must have held the equivalent of 50 cups, and even though we were baking daily for retail sales, it lost its effectiveness before we used it up.
Many factors come into play – moisture and temperature being key. Most brands suggest a six-month (perhaps a year) shelf life, so if you don’t bake a lot, chances are your tin has been hanging around your pantry for a while and should be replaced. As far as storage is concerned, most baking powders come in a tin that can be sealed airtight and they work quite well – as long as you seal the tin well after use. Also, always use a dry spoon in the container, then store in a cool location, such as a cabinet, but not the one over the stove.
As for testing the efficacy of your baking powder, it is quite simple. Measure ¼ cup very hot tap water (as hot as you can make it) into a measuring cup. Quickly stir in 1 teaspoon of baking powder and hopefully you will see lots of bubbles and even hear it make a fizzing sound. The bubbles and the sound will cease rather quickly, but if they do appear you are good to go. No bubbles or sound? Toss the tin.
Image: Dédé Wilson