Fermentation

Fermentation is the digestion of some matter by bacteria or other small organism (such as yeast).

Fermentation is popularly taken to refer to the fermentation of sugar in solution to alcohol using yeast.

In the process, the organism metabolises one or more substances to produce the energy and chemicals it needs to live and re-produce. This process of chemical reactions will produce some form of by-product. In the case of yeast used for brewing, these by-products are carbon dioxide, and ethanol alcohol.