Bread rises because yeast consumes sugars and releases carbon dioxide gas into the dough.

The longer version

Yeast are single-celled fungi that metabolize simple sugars and give off carbon dioxide and alcohol as byproducts. In dough, the gas has nowhere to escape because the kneaded mixture of flour and water forms an elastic network of gluten strands that stretches around each bubble. Warmth speeds the fermentation, while cold slows it.

Salt and sugar affect the rate too, since both change how much water is available to the cells. The alcohol produced during fermentation mostly evaporates in the oven. When the loaf finally meets heat, the trapped bubbles expand before the structure sets, which is why the increase in volume is most dramatic in the first minutes of baking.

Where this entry sits

Everyday ingredients turn out to be full of quiet chemistry and long history. This collection gathers short, plain explanations of how bread rises, why onions sting, where common spices originate, and how coffee, tea, and chocolate reached the modern kitchen. The full list sits on the Food and Drink page, where every entry is listed in order.