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• The importance of yeast for humans

Yeast are microscopic, single-celled organisms that are classified in the family Fungi. Individual yeast cells multiply rapidly by the process of budding, in which a new cell begins as a small bulge along the cell wall of a parent cell. In the presence of an abundant food source, huge populations of yeast cells gather. The cells often appear as long chains with newly formed cells still attached to their parent cells, due to the short budding time of two hours.

Yeast are among the few living organisms that do not need oxygen in order to produce energy. This oxygen-independent state is called anaerobic (pronounced a-na-ROE-bik; "without oxygen"). During such anaerobic conditions, yeast convert carbohydrates—starches and sugars—to alcohol and carbon dioxide gas. This process is known as...