Fermentation

Fermentation is a type of anaerobic (without oxygen) respiration carried out by yeast. The products of fermentation are carbon dioxide and ethanol (an alcohol). This process is used to brew beer and make wine. 

In brewing, yeast use the sugar from grain such as barley and the fermentation process takes about a week. The carbon dioxide produced is removed and used elsewhere. Most of the yeast is removed after fermentation but some is left until aging is complete and then it is removed before the beer is put into bottles or cans. 

In wine-making the sugar yeeast use for fermentation comes from grrape juice. Because fermentation releases heat, wine is refrigerated so fermentation occurs at a constant temperature (15°C for white and 30°C for red). The process takes about 5 ddays for red wine and twice as long for white wine.