A beer fermented entirely or primarily with Brettanomyces yeast — producing distinctive funky, leathery, fruity, and earthy character without necessarily being sour. Typically 4.5–9.0% ABV. Brett Beer is a relatively young category, championed by American craft brewers exploring what 100% Brett fermentation can produce when freed from the traditional Belgian framework of mixed cultures.
In the glass
Origin
Brettanomyces was first isolated and named in 1904 by Niels Hjelte Claussen at the New Carlsberg brewery’s laboratory, who identified it as the organism responsible for the distinctive flavor that developed in aged English stock ales during their slow secondary fermentation. The name means “British fungus.” The genus had long been present in the brewing world as a character-defining organism in Belgian lambic and a contaminant elsewhere, and the Belgian Trappist beer Orval, first brewed in 1931, has used Brettanomyces in its conditioning continuously through the decades when most breweries worked to eliminate it. Early-21st-century American craft brewers — among them Russian River, Allagash, and Crooked Stave — began fermenting beers with Brettanomyces as the sole or primary yeast, a deliberate departure from lambic’s mixed-culture tradition. The approach produces distinctly different results: fruity and funky, but generally not sour, showcasing what Brettanomyces alone can contribute to a finished beer.
Notes
Brett beer is best understood against its sour cousins. A 100% Brett beer is not the same as a lambic or a Flanders red: those derive their acidity from lactic and acetic bacteria working alongside wild yeast, while a Brett-only beer leans on the yeast’s esters, phenols, and funk and stays close to dry rather than tart. The category can range from pale and quenching to dark and malt-focused; what unifies it is the dominant Brettanomyces character rather than any particular base beer. Modern breweries have isolated dozens of distinct strains, which is why two Brett beers can smell worlds apart — one all tropical pineapple, another all hay and leather.
Defining examples
Allagash FV 13·Russian River Sanctification·Crooked Stave Hop Savant·Orval (traditional Belgian example, Brett-secondary)·Jester King Le Petit Prince (with Brett)