If your cream of tartar is still sealed in its original container, you’re in for a treat. It can last indefinitely—yes, you read that right. It won’t expire in any dangerous way, so you can safely assume that jar from 2015 is still good to go.
However, “indefinitely” doesn’t mean it’ll stay perfect forever. Over time, the powder can absorb moisture from the air, which might cause it to clump into little rocks. Think of them as tiny, edible fossils.
