Brettanomyces, sometimes called brett, one of the yeast genera found occasionally on grapes but more often in wines, especially those that have undergone barrel maturation or cask ageing. Brettanomyces in its perfect or sporulating form is known as dekkera, but recent changes to the rules for naming fungi suggest precedence be given to the name Brettanomyces. While it is widely considered a spoilage yeast since it can produce off-flavours in wines, there are producers who suggest that at low levels some of the diverse flavours produced by Brettanomyces can improve red wine complexity. (In some beers, for example Belgium’s spontaneously fermented lambic and gueuze beers, Brettanomyces and its effects are essential.)
