Cambridge O Level Biology · Syllabus 5090 · Biotechnology and Genetic Modification
Yeast in bread making
What is Yeast in bread making?
The use of yeast to raise bread dough. Yeast is mixed into dough containing a sugar source and respires anaerobically, converting glucose to ethanol and carbon dioxide. The carbon dioxide is released as bubbles that become trapped in the stretchy dough; as more gas is produced and the bubbles expand, the dough rises. Baking then kills the yeast, evaporates most of the ethanol and sets the structure so that the risen shape is permanent. The gas responsible for the rise is carbon dioxide - not ethanol, which is a liquid, and not oxygen, which is not a product of respiration.
This definition is part of the Biotechnology and Genetic Modification chapter in Cambridge O Level Biology.