Baking soda vs baking powder: how they differ
Quick answer: baking soda is pure sodium bicarbonate and needs an acid in the recipe to work. Baking powder is baking soda mixed with a dry acid, so it works on its own. They are not interchangeable one for one.
How each one works
Baking soda (sodium bicarbonate) is a base. When it meets an acid such as buttermilk, yogurt, lemon juice, brown sugar, honey or natural cocoa, it reacts and releases carbon dioxide bubbles that lift the batter. It starts working as soon as it gets wet, so bake soon after mixing.
Baking powder contains baking soda plus one or more powdered acids and a little starch to keep it dry. Most baking powder is double-acting: it releases some gas when mixed with liquid and more when heated in the oven.
Which does a recipe use?
- A recipe with an acidic ingredient (buttermilk, yogurt, brown sugar, cocoa) often uses baking soda, and sometimes both.
- A recipe with no acid (plain milk, white sugar) usually uses baking powder.
Recipes often use both, because the soda neutralizes the acid and the powder gives extra lift.
Typical amounts
As a rough guide, recipes use about 1 teaspoon of baking powder or 1/4 teaspoon of baking soda per cup of flour. Too much of either makes food taste soapy or metallic and can make it rise, then collapse.
Substituting one for the other
| You need | Use instead |
|---|---|
| 1 tsp baking powder | 1/4 tsp baking soda + 1/2 tsp cream of tartar |
| 1 tsp baking soda | About 3 tsp baking powder |
The second swap works, but the extra powder can add a slightly salty or chemical taste and changes the texture, so it suits recipes with little other flavor. You may also need to cut the salt slightly.
Substituting powder for soda in a recipe that uses acidic ingredients leaves that acid unbalanced, which can make the result taste sour. When in doubt, use what the recipe asks for. Need an acid? See the buttermilk substitute.
Test whether yours still works
Old leavener stops working. Test it in two minutes:
- Baking powder: stir 1 teaspoon into 1/2 cup of hot water. It should fizz right away.
- Baking soda: stir 1/4 teaspoon into 1 tablespoon of vinegar. It should fizz strongly.
If nothing happens, replace it. Most baking powder lasts about 6 to 12 months once opened.
Frequently asked questions
Can I use baking soda instead of baking powder? Not directly. Use the cream of tartar swap in the chart.
Are they the same as bicarbonate of soda? Baking soda is bicarbonate of soda, the British name.
Why did my cookies spread? Too much leavener, warm dough or too little flour can all do it. Measure carefully: see how to measure flour correctly.
To scale small spoon amounts, use the teaspoons to tablespoons converter.