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 a dietary supplement for its B vitamin content.
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 produce fewer of the esters that cause the fruity taste in ale, leaving a crisper taste, and work well at low temperatures. An example of bottom fermenting yeast 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.
- Main article: Brettanomyces
A genus of "wild" yeast used in brewing lambic. There are three main species: Brettanomyces lambicus; Brettanomyces bruxellensis; and Brettanomyces claussenii, which is found in Britain.
Due to its rapid metabolism, yeast contains a high concentration of the B vitamins, whose functions are related to metabolism, as well as other minerals and cofactors required for growth. It can therefore serve as a good dietary supplement of these nutrients. "Brewer's yeast" can also refer loosely to any nutritional yeast. S. cerevisiae is the usual species for this purpose.
Side effects have not been reported from the use of brewer’s yeast, although allergies to it exist in some people. It is not related to Candida albicans fungus, which causes yeast infection.
Because it contains a highly biologically active form of chromium, supplementation with brewer’s yeast could potentially enhance the effects of drugs for diabetes (e.g., insulin or other blood sugar-lowering agents) and possibly lead to hypoglycemia. Therefore, people with diabetes taking these medications should not supplement with chromium or brewer’s yeast without a doctor's supervision.
Saccharomyces cerevisiae is registered in Europe under the name Saccharomyces boulardii, though the manufacturer states that S. boulardii is not the same as brewer’s yeast (S. cerevisiae). It is marketed as a probiotic supplement for the treatment of diarrhea and Clostridium difficile colitis. There is a case report of a person with severely impaired immune function who, after receiving treatment with S. boulardii, developed an invasive fungal infection identified as S. cerevisiae. People with severe impairment of the immune system should therefore not take brewer’s yeast or S. boulardii unless supervised by a doctor.
Use of brewer's yeast as a dietary supplement is thought by some to effectively prevent parasitic insect bites and stings, e.g., mosquitoes.
Certain medicines may interact with brewer’s yeast. Refer to drug interactions for a list of those medicines.