Brettanomyces (Brett)

Definition - What does Brettanomyces (Brett) mean?

Brettanomyces, or Brett for short, is a naturally occurring yeast that is most commonly associated with wine spoilage or fault. In high doses, Brett causes rancid, barnyard or horsey aromas and characteristics in wine. Wines spoiled by Brett are called Bretty and metallic, or deemed to have Brett character. In low doses, it can add complexity and character to wines.

Brett is also known as Dekkera, however they are two different versions of the same genus of yeast: Brett does not populate through spores, while Dekkera does.

WineFrog explains Brettanomyces (Brett)

Brett produces several compounds that alter palate and bouquet. These are:

  1. 4-ethylphenol: creates band-aid, barnyard, horse stable, antiseptic notes
  2. 4-ethylguaiacol: creates bacon, spices, cloves and smoke notes
  3. Isovaleric acid: creates sweaty saddle, cheese and rancid notes
4-ethylphenol is the most common compound when Brett is present. It is balanced by the more favorable 4-ethylguaiacol in a ratio of 3:1 to 10:1. Winemakers who use Brett to create specific characters in their wine aim to use 420 micrograms/liter or less of 4-ethylphenol. The use of Brett in a wine reduces the fruit and typicity of a wine, but when used appropriately can add smoke, spice and earthy characters. Wines with high levels of Brett smell and taste like a rancid, dirty barn.

Brett thrives in wines with high polyphenol and pH content - which is why it is most common in red wines and very few whites (Sauvignon Blanc, Chardonnay). Some reds, especially those made for barrel aging, are more prone to Brett contamination than others. That’s why the winemaker has to aware of the causes and solutions.
Since the 1990s, Brett has been on the rise in winemaking. It is more prominent in natural winemaking practices - where winemakers don’t use pesticides or chemical additives - because "cure" for Brett is sulfur dioxide or other similar chemicals. Another cause of Brett is the "international" style of creating wines high in alcohol and sugar. High sugar content means the wine is also high in phenols and pH, two states that Brett loves. Also, residual sugars or nitrogen sources remaining in the wine when it is bottled allows the Brett to continue working and fermenting the wine, sometimes without the winemaker even knowing. Finally, old wine barrels (used for aging wines) can be a ripe breeding ground for Brett.