microorganism metabolises alcohol carbon dioxide wort top-fermenting Saccharomyces cerevisiae bottom-fermenting Saccharomyces pastorianus Brettanomyces lambics Torulaspora delbrueckii weissbier lambics cultures fermentation sugars yeast
Yeast is the microorganism that is responsible for fermentation in beer. Yeast metabolises the sugars extracted from grains, which produce alcohol and carbon dioxide, and thereby turns wort into beer. In addition to fermenting the beer, yeast influences the character and flavour. The dominant types of yeast used to make beer are top-fermenting Saccharomyces cerevisiae and bottom-fermenting Saccharomyces pastorianus. Brettanomyces ferments lambics, and Torulaspora delbrueckii ferments Bavarian weissbier. Before the role of yeast in fermentation was understood, fermentation involved wild or airborne yeasts. A few styles, such as lambics, rely on this method today, but most modern fermentation adds pure yeast cultures.
