top-fermenting yeast bottom-fermenting yeast Lactobacillus Brettanomyces lambics spontaneous fermentation fermentation beers wort lambic ales alcohol yeast yeasts
A variety of yeasts are used in making beer, most of which are strains of either top-fermenting yeast or bottom-fermenting yeast. Different strains impart different flavour and aroma characteristics, and may vary in which complex sugars they can ferment and how high their alcohol tolerance is, both of which are factors in attenuation. Some beers use other microbes in addition to yeasts, such as Lactobacillus or Brettanomyces. For example, the distinctive flavour and aroma of Belgian Abbey ales largely result from the yeast strains used to ferment the beer. There are a few modern styles, notably lambics, where spontaneous fermentation is used — that is, rather than being inoculated in a controlled fashion with a nurtured yeast, the unfermented wort is allowed to be colonised by microorganisms present in the environment.
