While staying at my grandparents’ house last weekend, I was craving pancakes—until I opened the baking cupboard and found a jar of baking soda with a label from the early 2000s. Could it still work?

I understand that baking powder has a shelf life, and that it can go bad. Can you tell us how long it remains good? Thank you. Joe and Kay, via e-mail It does have a shelf life, and here's how to test ...