Does Baking Powder Go Bad?
You bet and it can ruin the best of baking intentions. I speak from experience.
It doesn’t go bad as much as flat. It just doesn’t have the ability to leaven the baked goods any longer.
So how do you know? Does it smell? is it discolored? No. You can’t tell by looking. Use this trick.
Take a little baking powder, add it to a little warm water–if it fizzes it’s still good. No fizz? Don’t waste your other ingredients, go buy some fresh baking powder and save yourself the heartache.