Glossary
Brettanomyces
A genus of yeast that ferments sugars Saccharomyces cannot and produces barnyard, leather, hay and pineapple character — a spoilage organism in most breweries and the defining organism of several Belgian styles.
Pronounced bret-an-oh-MY-seez.
Also called brett, brettanomyces bruxellensis, dekkera.
The full record
Brettanomyces has its own catalogue entry with the detail this page summarises — causes, thresholds, related styles and evidence.
Brettanomyces — A wild yeast genus producing barnyard, leather and tropical-fruit character — a defect in most beer and the point of lambic.
Brettanomyces works slowly and consumes long-chain carbohydrates and cellulose-derived sugars, which is why it can keep a lambic developing for years after ordinary fermentation would have finished.
Whether it is a fault depends entirely on intent. In a pilsner it is contamination; in a gueuze it is the point. It is also notoriously difficult to eliminate from wood and soft plant components, which is why breweries that use it deliberately often keep separate equipment.
Commonly misunderstood
Brett is often described as "wild yeast". It is a specific genus, routinely pitched deliberately as a pure culture, and its presence says nothing about whether a fermentation was spontaneous.
Related
- Saccharomyces — The genus that does most brewing fermentation.
- Mixed fermentation — Where it is used deliberately.
- Gueuze — The style it defines.
- Brettanomyces — The catalogue record.
More vocabulary
Adjunct · Aroma hop · Base malt · Bittering hop · Black malt · Candi sugar · Chocolate malt · Crystal malt · Dextrin · Dual-purpose hop
See every term on the glossary index.
Last reviewed 2026-08-16.