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Why does bread get bigger when it is cooking?

MATERIAL WORLD: Room 1, Hampton Hill School, Tawa asked this question

Bread is made using yeast. Yeast is a living organism that converts the sugars in the bread mixture into carbon dioxide gas, the bubbles of which get trapped and make the bread rise and expand. Baking powder and baking soda are also used in baking, in place of yeast, as they react to form carbon dioxide gas which in turn makes the cakes and cookies expand and become lighter in texture, yum!

Our expert

Professor Sally Brooker answered this question. She is a Fellow of the Royal Society Te Apārangi, which means she’s one of the top experts in her field. She is based at University of Otago's chemistry department. See her profile.