microorganism metabolises alcohol carbon dioxide wort Saccharomyces cerevisiae Saccharomyces pastorianus Brettanomyces lambics Torulaspora delbrueckii weissbier lambics Emil Christian Hansen Carlsberg Laboratory cultures fermenting yeast brewery beer
Yeast is the microorganism that is responsible for fermentation in beer. Yeast metabolises the sugars extracted from grains, which produces 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 Saccharomyces cerevisiae, known as ale yeast, and Saccharomyces pastorianus, known as lager yeast;  Brettanomyces ferments lambics, and Torulaspora delbrueckii ferments Bavarian weissbier. Before the role of yeast in fermentation was understood, fermentation involved wild or airborne yeasts, and a few styles such as lambics still use this method today. Emil Christian Hansen, a Danish biochemist employed by the Carlsberg Laboratory, developed pure yeast cultures which were introduced into the Carlsberg brewery in 1883, and pure yeast strains are now the main fermenting source used worldwide.
