Baking Powder Shelf Life

What’s the best way to store baking powder? Does it go bad?

Baking powder is a chemical leavener that produces carbon dioxide (the gas that gives baked goods their lift) when mixed with liquid. It is made of baking soda, acid salt (such as cream of tartar), and cornstarch, which helps prevent the other two active ingredients from reacting with moisture in the air. Baking powder will lose its ability to produce carbon dioxide over time; most producers claim that it will last about one year once opened if stored properly in a dry, cool place.

To put this to the test, we opened new cans of baking powder at monthly intervals over the course of a year. After 12 months, we gathered the opened cans and began our testing by adding 1 teaspoon of powder to 1/2 cup of warm water—a common test to see if baking powder is still effective. All of the powders (even the one that had been opened for a year) made the water bubble and thus passed this test.

But we were skeptical that these powders all had equal leavening ability, so we whipped up a batch of biscuits with each—and saw a big difference. The rise began to decrease with the 6-month-old powder and continued to decline to half the height of fresh at the 10-month mark. So instead of relying on the bubbling water test, we recommend writing the date you open your baking powder right on the can and discarding open baking powder after six months.