Yeast has something to do with any of certain unicellular fungi, generally members of the class Ascomycetaceae, few are members of the class Basidiomycetaceae.

Many yeasts are capable of producing ethanol and carbon dioxide by the anaerobic fermentation of sugars. Yeasts are composed of approximately 50 per cent protein and are a rich nutritional source of B vitamins. Below are kinds of yeast:

1. Baker's yeast refers to a cultured yeast sold in grocery stores

2. Wild yeast- referring to a yeast that occurs naturally on the skins of fruit, on raisins, and in dust in the air