Brewer's yeast

Brewer's yeast consists of single-celled fungi of the genus Saccharomyces. They metabolise the sugar in the wort and produce alcohol, carbon dioxide and numerous flavour compounds. A distinction is made between top- and bottom-fermenting strains.

The yeast strain used strongly influences a beer's character: wheat beer yeasts contribute banana and clove, Kölsch yeasts mild fruitiness, lager yeasts a clean taste. Breweries often maintain their yeast strains for many years and reuse them after fermentation. If yeast remains in the finished beer, as in Hefeweizen or Zwickelbier, it appears cloudy. Filtered beer is almost free of yeast.