I tossed it, but, like my friend, I sometimes have some in my pantry that’s not the freshest and wonder: At what point is baking powder too old to use? With baking season upon us, you’ll ...

In fact, I learned the hard way about best-use-by-dates when we tried baking a cake with an old can of baking powder. I’ll bet you can guess what happened — we ended up with a flat cake.