Why the ratio works
Baking powder is baking soda pre-mixed with an acid (usually cream of tartar) and a little cornstarch. One teaspoon contains about 1/4 tsp of actual soda — that is why the substitution is 1 tsp baking powder → 1/4 tsp soda + 1/2 tsp cream of tartar.
Mixing it yourself
- Whisk the soda and cream of tartar with the dry ingredients so the acid is evenly distributed
- Use immediately — the mixture starts reacting as soon as it meets liquid
- No cream of tartar? Use 1/4 tsp soda plus 1/2 tsp lemon juice or vinegar in the wet ingredients
- Do not substitute baking soda alone — without acid it leaves a soapy taste and poor rise
Single-acting versus double-acting
Most supermarket baking powder is double-acting: it releases gas once when mixed and again in the oven. A homemade soda + cream of tartar mix is single-acting, so get the batter into the oven promptly.
When not to substitute
Recipes that already contain an acid (buttermilk, yoghurt, lemon) may rely on that acid activating added soda. Swapping in more acid can over-activate and collapse the crumb — check the recipe's liquid before changing the leavening.
Frequently Asked Questions
Can I use baking soda instead of baking powder?
Only with an acid. 1 tsp baking powder = 1/4 tsp soda + 1/2 tsp cream of tartar.
Does the substitute taste different?
Slightly — cream of tartar can leave a faint tang in large amounts.
Is self-raising flour the same?
No; it already contains baking powder. Adjust the recipe rather than adding more.
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