Brettanomyces

Brettanomyces is a genus of yeast (true fungi) known for its role in the fermentation and aging of beer and wine. It is often described as a wild or spoilage organism, but it is also intentionally exploited in some beer styles to add complexity. The genus includes several species, most notably Brettanomyces bruxellensis, along with B. anomalus, B. lambicus, and B. custersianus; in some classifications, the sexual form of B. bruxellensis is called Dekkera bruxellensis.

Ecology and physiology: Brettanomyces yeasts tolerate low nutrient availability, acidic conditions, and relatively high ethanol. They grow slowly and are able to metabolize a wide range of carbon sources, often persisting in wooden barrels, casks, and other porous environments where Saccharomyces is less competitive.

Flavor and aroma: They produce volatile phenols such as 4-ethylphenol and 4-ethylguaiacol, giving earthy, smoky, spicy, or "barnyard" notes sometimes described as horse blanket. They can also form esters and glycerol that contribute to sweetness and mouthfeel. In beer, Brettanomyces can be perceived as off-flavors, but in certain styles they provide desirable complexity when well managed. In wine and barrel-aged beer, they can contribute to character over extended aging.

Applications and contexts: Brettanomyces is central to traditional Belgian lambic and Gueuze beers and to some sour ales fermented with mixed cultures. In many beer and wine production systems, it is considered a contaminant to be controlled; in others, it is a valued contributor to aging profiles.

Management and detection: Controlling Brettanomyces relies on sanitation, oxygen management, and careful handling of wooden vessels. It is often monitored by selective culturing on specialized media and by molecular methods such as PCR to detect its DNA in product samples.