species
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 can ferment dextrins that Saccharomyces leaves behind, so a Brett-inoculated beer keeps attenuating for months or years and finishes exceptionally dry. That super-attenuation is also why it is dangerous in packaged beer that was not meant to contain it: continued fermentation in the bottle produces gushers or worse.
Its character is genuinely variable and develops with time — young Brett is often tropical and pineapple-like, while mature Brett moves toward leather, hay and horse blanket.
The name means "British fungus"; it was first isolated in the context of English stock ale, where a degree of its character was expected in aged beer.
Behaviour
| Scientific name | Brettanomyces bruxellensis |
|---|---|
| Apparent attenuation | 85–100% |
| Flocculation | low |
| Esters | high |
| Phenols | high |
Used in
- Old ale
A matured English strong ale with dried fruit, treacle and often a trace of oxidative or wild character from age.
- Berliner Weisse
A very low-strength sour wheat beer: sharply lactic, bone dry, lightly sparkling and enormously refreshing.
- Lambic
Spontaneously fermented Belgian wheat beer, matured in oak for years — funky, acidic, dry and unlike any other beer.
- Gueuze
A blend of young and old lambic, refermented in bottle — intensely complex, bone dry and Champagne-like in its carbonation.
- Fruit lambic
Lambic refermented on whole fruit — traditionally sour cherry or raspberry — producing a dry, tart, intensely fruity beer.
- Flanders red ale
A deep red sour ale matured for years in oak foeders, balancing sharp acidity against dark fruit and a vinous depth.
- American wild ale
A broad New World category of mixed-fermentation and barrel-aged sour beers, often fruited, with no fixed base style.
Questions
Is Brettanomyces a contamination or an ingredient?
Both, depending on intent. In a lager or a fresh IPA it is a contamination that will keep fermenting in the package and eventually produce gushing bottles. In lambic, gueuze, aged saison and traditional old ale it is a deliberate and essential ingredient. The organism is identical; the difference is whether the brewer chose it.
Evidence
What BeerHQ knows about this, and how. Every statement carries the state of the evidence behind it rather than being presented flatly as fact.
Brettanomyces is a specific genus routinely pitched as a pure culture, so its presence indicates neither a spontaneous fermentation nor an accident — the common description of it as "wild yeast" conflates the organism with a method.
Backed by a source
Sources: Yeast: The Practical Guide to Beer Fermentation — print; The Oxford Companion to Beer — print
Brettanomyces can consume long-chain carbohydrates that Saccharomyces cannot, which is why a mixed or spontaneous fermentation keeps developing for years after ordinary fermentation would have finished.
Backed by a source
Sources: Yeast: The Practical Guide to Beer Fermentation — print; Journal of the Institute of Brewing