Yeast

Yeast is a collection of single-cell fungi. It is an ingredient in baking as it causes dough to expand by converting sugar and starch to alcohol and CO₂. The gas inflates the dough and the alcohol is evaporated. Yeast is also used in the manufacture of alcoholic beverages to ferment sugars of rice, wheat, barley, and corn and to create the bubbles in sparkling drinks such as champagne.

Yeast is 50% protein and is sold as a food supplement in health stores.

Active raw yeast should never be ingested as it will continue to grow in the digestive system and consume nutrients which would otherwise be utilized by the body. Pasteurization prevents that from occurring.