Article: Brewer's yeast

Brewer's yeast (also known as brewers yeast or brewing yeast) can mean any live yeast used in brewing. It can also mean yeast obtained as a by-product of brewing, dried and killed, and used as nutritional yeast.

Beer brewing

Beer brewers classify yeasts as top-fermenting and bottom-fermenting. This distinction was introduced by the Dane Emil Christian Hansen.

Top-fermenting yeasts (so-called because they float to the top of the beer) can produce higher alcohol concentrations and prefer higher temperatures. An example is Saccharomyces cerevisiae, known to brewers as ale yeast. They produce fruitier, sweeter, ale-type beers. Bottom-fermenting yeasts ferment more sugars, leaving a crisper taste, and work well at low temperatures. Another example is Saccharomyces uvarum, formerly known as Saccharomyces carlsbergensis. They are used in producing lager-type beers. Brewers of Bavarian-style wheat beers often use varieties of Torulaspora delbrueckii, which contribute to the distinctive flavour profile.

To ensure purity of strain, a 'clean' sample of the yeast is stored in a laboratory environment at refrigerated temperature. After a certain number of fermentation cycles, a full scale propagation is produced from this laboratory sample. Typically, it is grown up in about three or four stages using sterile Brewing wort and oxygen.

Brettanomyces

Main article: Brettanomyces

A notable "wild" strain of yeast used in brewing lambic. There are three main strains: Brettanomyces lambicus; Brettanomyces bruxellensis; and Brettanomyces claussenii, a British strain.

Nutritional yeast

"Brewer's yeast" can also refer loosely to any nutritional yeast. S. cerevisiae is the usual species for this purpose.^[1]

See also

• Bottom and top fermenting yeast
• Brettanomyces