Brewer's yeast
Brewer's 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. S. cerevisiae is the usual species for this purpose.[1] "Brewer's yeast" can also refer loosely to any nutritional yeast.
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, real ale-type beers. Bottom-fermenting yeasts ferment more sugars, leaving a crisper taste, and work well at low temperatures. An example is Saccharomyces uvarum, formerly known as Saccharomyces carlsbergensis. They are used in producing lager-type beers. Brewers of wheat beers often use varieties of Torulaspora delbrueckii.