Baking Soda vs Baking Powder
Baking soda is pure sodium bicarbonate, a base that releases carbon dioxide only when it meets an acid. Baking powder is baking soda already mixed with powdered acid and a little starch, so it can leaven a batter on its own with just moisture and heat.
How baking soda works
Baking soda reacts instantly with acidic ingredients: buttermilk, yogurt, sour cream, brown sugar, molasses, honey, natural cocoa, lemon juice, or vinegar. The reaction releases carbon dioxide gas and leaves behind a neutral salt.
It's strong. About ¼ teaspoon leavens a cup of flour, roughly 3–4 times the power of baking powder. Because it starts reacting as soon as it's wet, batters using only soda should go into the oven quickly.
Baking soda also raises pH. A more alkaline batter browns faster through the Maillard reaction, which is why soda gives cookies deeper colour and more spread. Too much, though, leaves a soapy, metallic taste.
How baking powder works
Baking powder contains three things:
- Baking soda (the base)
- One or two dry acids, such as cream of tartar, monocalcium phosphate, sodium aluminum sulfate, or sodium acid pyrophosphate
- Cornstarch, to absorb moisture and keep them from reacting in the tin
Most grocery-store baking powder is double-acting. One acid reacts when the batter gets wet; the second waits for oven heat. That two-step release gives a reliable rise even if batter sits for a few minutes.
Side by side
| Baking soda | Baking powder | |
|---|---|---|
| What it is | Sodium bicarbonate | Soda + dry acid + starch |
| Needs an acid ingredient? | Yes | No |
| Strength | About 3–4× stronger | Milder |
| Effect on browning | Increases | Neutral |
| Typical amount per 125 g (1 cup) flour | ¼ tsp | 1–1¼ tsp |
Why recipes use both
Buttermilk pancakes are a classic case. The soda neutralizes buttermilk's acidity for better flavour and browning, but there isn't enough of it to provide all the lift without leaving a soapy taste. Baking powder covers the rest.
Substitutions
- Replace 1 tsp baking powder with ¼ tsp baking soda + ½ tsp cream of tartar.
- Replace ¼ tsp baking soda with about ¾ tsp baking powder.
For more options, see baking powder substitute and baking soda substitute.
Storage
Keep both tightly closed in a cool, dry cupboard. Once opened, baking powder loses strength in about 6–12 months. Baking soda lasts longer but can absorb odours, so don't share the box you use in the fridge.
Questions
Can I use baking powder instead of baking soda?
Yes, in a pinch. Use about 3 times as much baking powder as the baking soda called for. Expect a slightly tangier flavour and less browning.
Can I use baking soda instead of baking powder?
Only if you add acid. For each 1 teaspoon of baking powder, use ¼ teaspoon baking soda plus ½ teaspoon cream of tartar, or swap some of the liquid for buttermilk or yogurt.
Why do some recipes use both baking soda and baking powder?
The soda neutralizes acidic ingredients like buttermilk, which balances flavour and boosts browning. The powder supplies the rest of the lift the soda alone can't provide.
How do you test if baking soda or baking powder is still good?
Stir ¼ teaspoon of baking soda into a spoonful of vinegar, or ½ teaspoon of baking powder into hot water. Strong, immediate fizzing means it's still active.