What if cakes had no baking powder?

A cake goes into the oven flat and runny. It comes out tall and soft!

Inside, it is full of tiny holes. What made the holes? And what if there were no baking powder?

Cake batter is a thick, runny mixture. Yet in the oven it grows taller and sets into something soft and spongy. Cut a slice and you'll find it full of tiny holes, like a sponge.

Those holes were once bubbles of gas. In many cakes, the gas comes from baking powder. So what if cakes had no baking powder? We can follow the clues: the gas, the bubbles, and the other ways bakers make things rise.

A cake owes its light, porous texture to leavening: the release or trapping of gas within a batter, which expands as it bakes and is then fixed in place as the structure sets. Layer cakes, muffins, cookies and biscuits are among the products leavened chemically.

This thought experiment removes baking powder and asks three questions: what it actually does, how gas bubbles shape a cake, and what other leavening methods, from beaten egg whites to yeast, could stand in. Established chemistry and reasoned guesses are labeled separately.

Baking powder is a powder. It is a mix of two things that react together.

When it gets wet and warm, it makes lots of tiny bubbles. The bubbles help the cake grow.

Baking powder looks like a plain powder, but it is really a mixture. It contains baking soda (sodium bicarbonate), a dry acid, and some starch to keep it fresh in the tin.

When the batter is mixed, the baking soda and acid can react, giving off bubbles of carbon dioxide gas and leaving behind salts with only a mild taste. Most baking powders sold today are double-acting: they make a little gas when you mix the batter and the rest when the oven heats it.

Britannica describes baking powder as a base, a carbonate or bicarbonate, mixed with a weak acid in suitable amounts, plus a diluent such as starch that acts as a buffer between them. The reaction's end products are carbon dioxide and blandly flavored, harmless salts.

The acid sets the timing. Single-acting powders, with tartaric acid or cream of tartar, release their gas at room temperature, so the batter must be baked at once. Double-acting powder, the most widely used type, contains sodium aluminum sulfate and calcium acid phosphate: it releases a small amount of gas on mixing and the rest when heated, so less gas is lost if the batter waits.

Now imagine the baking powder is gone. No powder means no extra bubbles.

The cake might come out flat and heavy. Some cakes could still rise in other ways.

Without baking powder, a cake made from an ordinary recipe would lose its main source of gas. With fewer bubbles to puff it up, the cake might come out flatter, heavier and less spongy. That is our prediction, based on what baking powder does.

But cakes would not vanish. Bakers already know other ways to get bubbles into a batter: beating in air, whipping egg whites into foam, and letting steam push up from inside. Some cakes, like sponge cakes and angel food cake, rely on beaten egg whites.

Leavening agents expand a batter by releasing gas, giving a porous structure. Remove the chemical leavening from a recipe designed around it and the main gas source is gone; a denser, less expanded crumb is the reasoned expectation, not a measured result.

Other leavening routes remain. Britannica lists air, steam, yeast and baking soda alongside baking powder. Vigorous mixing traps air; egg white forms voluminous, strong foams that hold their structure as they bake, and is used in angel food, chiffon and sponge cakes. Baking soda alone works if the recipe supplies an acid, such as honey, sour cream, molasses or cocoa.

Gas takes up space. When bubbles grow, the batter gets bigger.

In the oven, the batter turns firm around the bubbles. The holes stay, and the cake stays soft and tall.

Every bubble in a batter is a little pocket of gas. Beating the batter traps tiny air bubbles, and baking powder adds carbon dioxide to them. In the hot oven, the bubbles grow bigger, and steam from the batter's water pushes on them too, so the whole cake swells.

Meanwhile, the heat makes the batter set firm around each bubble, with the holes inside it. If the gas all escapes too early, before the cake has set, the cake can sink.

Leavening is a race between gas and structure. Beating fat into a batter traps many tiny air bubbles; chemical leavening releases carbon dioxide; and as the interior nears the boiling point, water vapor exerts pressure inside the bubbles, producing further swelling. Gluten proteins from the flour are the main structural element that sets around the cells.

Timing matters. The New Zealand Institute of Chemistry notes that if too much carbon dioxide is released at first and production stops, the cake can drop when it leaves the oven, which is why some powders combine a fast acid with a slower one.

Bread rises too, but not with baking powder. It uses yeast.

Yeast is made of tiny living cells. They eat sugar and make bubbles of gas.

For thousands of years, people have raised bread with living leavening. Baker's yeast is made of tiny living cells. Mixed into a dough, the yeast feeds on sugars and gives off carbon dioxide, along with substances that add flavor and smell. That is why most breads and rolls, and some sweet treats like raised doughnuts and Danish pastries, are made with yeast.

A yeast dough is left to rise, often to about double its size, before baking. Cakes, muffins and cookies are among the treats raised with baking powder or baking soda instead.

Leavening with living things is very old. Britannica credits the Egyptians, by 2600 BCE, with the first intentional use of leavening: they kept stocks of sour dough to start fresh doughs. Bread samples found in their tombs are flatter and coarser than modern bread.

Baker's yeast, Saccharomyces cerevisiae, ferments sugars in the dough, releasing carbon dioxide and flavor compounds. Sourdough relies on sugar-fermenting bacteria in a starter. Yeast leavens most breads and rolls and sweet doughs such as coffee cakes and Danish pastries, while chemical leaveners raise layer cakes, cookies, muffins, biscuits and corn bread.