Brewer's yeast

Brewer's yeast is a fermentation by-product made of inactivated Saccharomyces cerevisiae cells, added to foods and supplements as a source of B-group vitamins, protein and palatability, and it often improves a food's taste, which explains its use in treats and [coating](/glossary/coating). It also supplies beta-glucans and mannans, cell-wall compounds studied for a possible role in gut flora and immunity, though clinical evidence for these effects in dogs and cats remains limited and does not justify strong claims (EFSA). A persistent myth credits brewer's yeast with repelling fleas; scientific data do not confirm this effect, so it should be presented as folklore rather than fact. Brewer's yeast is a safe ingredient in reasonable amounts, useful mainly for palatability and B-vitamin supply, and importantly it should not be confused with raw baker's yeast, which can ferment in the stomach and cause problems. The inactivated yeast found in foods carries no fermentation risk (FEDIAF). The marker: brewer's yeast is a safe palatability and B-vitamin ingredient whose immune and anti-flea claims outrun the evidence, a pattern it shares with several functional additives in the [Petipedia glossary](/glossary). Its influence on taste links to broader questions of [palatability](/glossary/palatability) and how it can flatter a [coating](/glossary/coating).

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