Why does yeast make bread rise? © Getty Images

Why does yeast make bread rise?

As if by magic, leavened breads rise as they are baked.

Asked by: Nicholas Peat, Kendal


Yeast is a single-celled fungus, and the cells are still alive when you mix them into the dough. The yeast releases enzymes that convert the flour starch into sugar, which the cells absorb and metabolise. This process releases CO2 gas, which forms bubbles that become trapped in the stretchy dough. During baking, the oven’s heat expands the bubbles even further.


Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.