What role does play yeast in breweries?

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 wortinto beer. In addition to fermenting the beer, yeast influences the character and flavour.[23] The dominant types of yeast used to make beer are Saccharomyces cerevisiae, known as ale yeast, and Saccharomyces uvarum, known as lager yeast; their use distinguishes ale and lager.[24] Brettanomycesferments lambics,[25] and Torulaspora delbrueckii ferments Bavarian weissbier.[26]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