Dough rises because yeast releases carbon dioxide during fermentation, and the gluten network inside the dough traps those bubbles. As a result, the dough expands and becomes lighter.
Explanation
Yeast feeds on simple sugars already present in the flour or created as starch breaks down. In the process, it produces gas and a small amount of alcohol. The gas inflates tiny pockets in the dough, and during baking those bubbles expand even more with heat, which is why the crumb becomes airy.
Details
Good rise depends on three things: active yeast, enough time, and an elastic structure. When dough is mixed, flour proteins form gluten, which works like a stretchy web. If the dough is undermixed, the gas escapes too easily and the rise is weaker. If the dough is left too long, the structure can weaken and collapse. Warmth speeds up fermentation, but excessive heat harms yeast, so dough usually needs a moderate temperature rather than real heat.
How sourdough works
Sourdough lifts dough for the same basic reason, but instead of commercial yeast it relies on wild yeast and lactic acid bacteria. When you feed a starter, you add fresh flour and often a little water. The microorganisms get a new food supply, become active, start processing sugars from the flour, and release gas. That is why the starter grows after feeding and can later leaven dough well.
Feeding is not a ritual for its own sake. It keeps the starter strong and stable. If it sits too long without food, the microorganisms weaken, acidity shifts, and dough rises more slowly. A healthy active starter usually shows many small bubbles, grows noticeably after feeding, and gives dough not only lift but also its characteristic tangy aroma.
Good to know
- Salt slows yeast down: it helps with flavor and fermentation control, but too much of it reduces rise.
- Cold fermentation is slower but often tastier: more time usually means deeper flavor and better texture.
- Sourdough works more slowly than commercial yeast: in return, it often gives fuller flavor, a different texture, and a stronger aroma.
- Yeast is not the only way dough can rise: some recipes use baking soda or baking powder, where gas comes from a chemical reaction instead of living microorganisms.
