Why Dough Rises: Kitchen Science Words

The Secret Inside Bread Dough

1Have you ever watched a lump of bread dough grow in a bowl on the kitchen counter? A ball of dough can double in size in an hour or two. It is not magic. The dough rises because of a tiny living helper called yeast.

2Yeast is a kind of fungus, so it is related to mushrooms. Each yeast cell is microscopic, which means it is far too small to see without a microscope. The dry yeast that families buy in small packets is dormant. It is alive, but it is resting and not growing. When a baker mixes the yeast with warm water, the yeast becomes active again.

3Next, the baker stirs in flour. Yeast feeds on the sugars in flour. As it feeds, it gives off a gas called carbon dioxide. This process is called fermentation. Carbon dioxide is the same gas that makes the bubbles in a fizzy drink.

4Gas alone cannot make bread rise. Something has to hold the gas in. That is the job of gluten. Gluten forms when proteins in wheat flour mix with water. When a baker kneads the dough, pressing, folding and pushing it over and over, the gluten forms long strands. These strands make the dough elastic. Elastic dough can stretch out and then spring back, like a rubber band.

5The gluten strands trap the carbon dioxide in thousands of tiny pockets, almost like little balloons. As more gas collects, the pockets expand, or grow larger, and the whole dough puffs up. Bakers call this resting and rising time proofing. Yeast works best when it is warm, so dough proofs more slowly in a cool kitchen.

6Finally, the dough goes into a hot oven. The heat makes the gas pockets expand one last time, and then the heat stops the yeast from working. The dough firms up around the pockets. Slice a loaf, and you can see the holes where the gas bubbles used to be. Bread made without yeast is often dense, which means it is heavy and packed tightly, with very few holes. Many flatbreads are made this way.