Brettanomyces

Brettanomyces, chiefly the species Brettanomyces bruxellensis, is a spoilage yeast producing volatile phenols, mainly 4-ethylphenol and 4-ethylguaiacol. Its animal aromas evoke leather, stable, medicinal plaster and barnyard. Able to survive without oxygen and to lastingly colonise wooden barrels, it divides tasters: a subtle trace judged complex by some, a clear fault masking the fruit for others. It most commonly affects ageing red wines held in barrel.