Brettanomyces is a non-spore forming genus of yeast in the family Saccharomycetaceae, and is often colloquially referred to as "Brett". The genus name Dekkera is used interchangeably with Brettanomyces, as it describes the teleomorph or spore forming form of the yeast. The cellular morphology of the yeast can vary from ovoid to long "sausage" shaped cells. The yeast is acidogenic, and when grown on glucose rich media produces large amounts of acetic acid. Brettanomyces is important to both the brewing and wine industries due to the sensory compounds it produces.
In the wild, Brettanomyces lives on the skins of fruit. The strain Brettanomyces claussenii was discovered at the Carlsberg brewery in 1904 by N. Hjelte Claussen, who was investigating it as a cause of spoilage in English ales. The term Brettanomyces comes from the Greek for "British fungus."