MARTYN F. CHILLMAID / SCIENCE PHOTO LIBRARY MARTYN F. CHILLMAID / SCIENCE PHOTO LIBRARY
Bread yeast. Packaged baker's or brewer's yeast, Saccharomyces cerevisiae, used to bake bread. Yeast is a kind of single-celled fungus. It is able to ferment sugar, producing alcohol and carbon dioxide in the process. It has long been used to make beer and wine as well as leavened bread (carbon dioxide causes the dough to rise).
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