First off, cream of tartar is not some magical fairy dust, though it does make meringues stand up like a soldier. It's actually potassium bitartrate, a byproduct of winemaking. Think of it as the hangover helper for your wine grapes, left behind in barrels. Because it's a dry, acidic powder, it has an incredibly long shelf life—almost like a cartoon dinosaur that refuses to die.
But expire is a tricky word. Your jar of cream of tartar won't suddenly grow green fuzz or start emitting noxious fumes. It's not a carton of milk that will ruin your morning cereal. Instead, its expiration is more like that friend who still tells the same joke from college: it loses its punch.
