Brett or brettanomyces is a high attenuation yeast strain that is known for the acidic, funky, wild\barnyard type tastes and smells that it produces. In most beer styles, brett it is perceived as an unwanted contaminant due to its strong and distinct flavors that can overwhelm more subtle beer flavors. Yet it is highly prized in some Belgian ales, such as gueuze, lambics, farmhouse ales, and Flanders red ales.
It is even used in one of my favorite Belgian Trappist beers called Orval, where their brewers add it at bottling, and allow it to ferment out and condition over time. Brettanomyces has grown in popularity over the last several years and is now used in a wide variety of styles and by many US craft breweries. When brewing with brett, it is important to avoid cross contamination with your non-brett beers as it is a robust yeast strain that can easily modify a beer’s flavor and aroma.
The most commonly used brett yeast strains are White Labs WLP644 Brettanomyces Bruxellensis Trois, White Labs WLP645 Brettanomyces Clausenii, White Labs WLP650 Brettanomyces Bruxellensis and Wyeast 5526 Brettanomyces Lambicus.