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?

Have you ever looked at a half-used tin of baking powder or cocoa and wondered, “Is this still okay to use?” You’re not the only one. Most of us dislike throwing away perfectly good ingredients. The ...