In the fermenter, the yeast converts the malt-sugar to alcohol, aroma and carbon dioxide. After fermentation, the yeast is being removed and the beer is ready for maturation. The fermentation will normally take between 3-30 days, dependent on the beer type and temperatures used.
Yeast is the soul of beer. Brewers use top-fermenting or bottom-fermenting yeast. Top-fermenting yeast rises while bottom-fermenting yeast falls to the bottom. Top-fermenting yeast contributes most to the aroma in beer. To produce one litre of beer you need around 10 grams of yeast.
Yeast multiplies during fermentation. Yeast can be used around 10 times, before being sold as spend yeast for protein production or as pig feed.