How to Test Baking Soda and Baking Powder (And What's the Difference?)
Flat cookies. Dense muffins. A cake that didn't rise. Nine times out of ten, it's the leavener. Here's how to know before you bake.
How to Test Baking Soda
Add ¼ teaspoon of baking soda to 2 teaspoons of white vinegar — or to hot water with a splash of vinegar stirred in. You'll see the result instantly: if it bubbles vigorously and foams up, your baking soda is still good. Weak fizz or no reaction at all means it's lost its strength. Toss it and open a new box.
How to Test Baking Powder
Add 1 teaspoon of baking powder to ½ cup of hot water. Strong, immediate bubbles mean it's still active and ready to lift your batter. If you barely see a reaction, replace it — flat baked goods are guaranteed otherwise.
Baking Soda vs. Baking Powder — What's the Difference?
They look almost identical, but they work differently. Baking soda is pure sodium bicarbonate. It needs an acid — buttermilk, yogurt, lemon juice, vinegar, brown sugar, cocoa — to react and release the carbon dioxide that lifts your batter.
Baking powder already contains baking soda plus a dry acid (and a little cornstarch to keep them apart). It activates when it hits moisture and again when it hits heat, which is why most modern baking powders are labeled "double-acting."
Because they work differently, they aren't interchangeable without adjusting the rest of the recipe.
How Long Do They Last?
Baking soda: roughly 6 months to 1 year once opened. An unopened box keeps for about 2 years.
Baking powder: 6 to 12 months once opened, up to about 18 months unopened.
Both last longer if you store them in a cool, dry place with the lid tightly closed. Heat and humidity are the enemies — keep them out of the cabinet right above the stove.
Can You Substitute One for the Other?
Yes, with adjustments. To replace 1 teaspoon of baking powder, use about ¼ teaspoon of baking soda plus an acidic ingredient already in (or added to) your recipe — buttermilk, yogurt, lemon juice or vinegar all work. Going the other way is trickier and rarely worth it.
Expect a slightly different flavor when you swap: too much baking soda without enough acid leaves a soapy, metallic aftertaste, while baking powder tends to be more neutral.
Scaling a recipe? Adjust every ingredient automatically →