Brettanomyces bruxellensis (the anamorph of Dekkera bruxellensis) is a yeast associated with the Senne valley near Brussels, Belgium.
B. bruxellensis plays a key role in the production of the typical Belgian beer styles such as Lambic, Flanders red ales, Gueuze, Kriek, and Orval, and is part of spontaneous fermentation biota. It is naturally found in the brewery environment living within oak barrels that are used for the storage of beer during the secondary conditioning stage. Here it completes the long slow fermentation or super-attenuation of beer, often in symbiosis with Pediococcus sp. Macroscopically visible colonies look whitish and show a dome-shaped aspect, depending on the age and size.
In the wine industry, B. bruxellensis is generally considered a spoilage yeast and it and other members of the genus are often referred to as Brettanomyces (“brett”). Its metabolic products can impart “sweaty saddle leather”, “barnyard”, “burnt plastic” or “band-aid” aromas to wine. Some winemakers in France, and occasionally elsewhere, consider it a desirable addition to wine.