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Why does yeast make bread rise?

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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.


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luis villazon
Luis VillazonQ&A expert

Luis trained as a zoologist, but now works as a science and technology educator. In his spare time he builds 3D-printed robots, in the hope that he will be spared when the revolution inevitably comes.


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