Why does yeast make bread rise?

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.

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