Leavening
Leavening is anything that makes a dough or batter rise by filling it with gas, which expands in the oven and sets into a light, airy texture. The gas can come from yeast, from chemical reactions with baking soda or baking powder, or from air and steam worked in physically.
The three kinds of leavening
Biological. Yeast and the wild microbes in a sourdough starter eat sugars and release carbon dioxide slowly. Gluten traps the gas, which is why bread needs time to rise.
Chemical. Baking soda (sodium bicarbonate) reacts with acid to release carbon dioxide almost instantly. Baking powder packs soda and dry acid together, often releasing gas twice: once when wet and again in the oven heat. See baking soda vs baking powder.
Mechanical and physical. Air beaten in by creaming butter and sugar or whipping eggs, plus steam from water in the dough. Water expands roughly 1,600 times in volume when it turns to steam, which is what puffs choux pastry, popovers, and laminated dough.
A surprising fact: leaveners don't make bubbles
Chemical leaveners and yeast don't create new bubbles. They release gas into tiny air pockets that are already there, made by mixing, creaming, or kneading. No air cells, no rise. That's why proper creaming and mixing matter so much in cakes.
What happens in the oven
As temperature climbs, three things push the rise:
- Gases expand with heat.
- Water and alcohol turn to vapour.
- Dissolved carbon dioxide escapes into the bubbles.
The rise ends once proteins and starches set, at roughly 70–85 °C (158–185 °F) inside the batter.
Typical amounts
| Leavener | Per 125 g (1 cup) flour |
|---|---|
| Baking powder | 1–1¼ tsp (about 4–5 g) |
| Baking soda | ¼ tsp (about 1 g), with an acid |
| Instant yeast (bread) | ½–1 tsp (about 1.5–3 g) |
Common problems
- Flat or dense: stale leavener, warm butter that couldn't hold air, or batter left sitting too long.
- Tunnels and peaked tops: too much leavening or overmixing.
- Sunken centre: too much leavening, underbaking, or opening the oven early.
- Soapy, metallic taste: too much baking soda for the amount of acid.
At high elevations, gases expand more readily, so recipes usually need less leavening (see high-altitude baking).
Questions
What are the three main types of leavening?
Biological leavening uses yeast or sourdough microbes, chemical leavening uses baking soda or baking powder, and mechanical or physical leavening uses whipped air or steam. Many baked goods combine more than one.
How much baking powder do you use per cup of flour?
A common rule is about 1 to 1¼ teaspoons of baking powder per 125 g (1 cup) of all-purpose flour. For baking soda, about ¼ teaspoon per cup of flour, balanced with an acidic ingredient.
Why didn't my cake rise?
Common causes are expired baking powder or soda, an oven that's too cool, under-creamed butter and sugar, or batter that sat too long before baking. Overmixing can also knock out air and toughen the crumb.
Can too much leavening make a cake fall?
Yes. Excess leavening makes bubbles grow too large, rise, and burst before the structure sets, so the cake collapses. It also leaves a bitter or soapy taste.