Leavening: baking soda, baking powder, yeast and steam

Chemical

• Baking soda (sodium bicarbonate) needs an acid (buttermilk, yogurt, brown sugar, natural cocoa, lemon) to release CO2. Too much without enough acid tastes soapy or metallic.
• Baking powder already contains soda plus dry acid(s). "Double-acting" releases some gas when wet and more when heated.
• Roughly, soda is about 3-4 times stronger than powder.

Biological and physical

• Yeast ferments sugars into CO2 slowly, with flavor.
• Steam puffs choux, popovers and puff pastry.
• Air whipped into eggs or creamed butter and sugar (sponge cake, meringue).

Freshness test

Baking powder: a spoonful in hot water should fizz. Baking soda: fizzes with vinegar. If not, replace it.

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Explain leavening in plain English for a home cook, with one kitchen experiment I can do to see it, and how it applies to [dish].
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Where these facts come from

• American Chemical Society: Reactions, food chemistry explainers
• Exploratorium: Science of Cooking
• USDA FSIS: Safe temperature chart
• FoodSafety.gov: Safe minimum internal temperatures
• Harold McGee, On Food and Cooking (Scribner, 2004): the standard reference on kitchen chemistry

Checked Oct 29, 2026. Temperatures given for reactions are typical ranges, not sharp switches; they shift with moisture, pH and time. Food-safety numbers always come from USDA/FoodSafety.gov.