Is it necessary to add yeast to alcoholic fermentation?
Fermentation of sugars to produce alcohol does require the presence of yeast, however, its not always necessary to add the yeast. For example, crushed grapes will start fermenting without addition of yeast because the skins contain natural wild yeast cells that will ferment. However, in order to make good wine, the grapes are usually sterilized and cultured yeasts developed especially for wine are added.
