Have you ever opened a bottle of wine and thought you’d stepped in something? That pungent aroma, politely called “barnyard,” is a telltale sign of Brettanomyces, a microbial spoiler of wine. Brett, as it is commonly called in wine circles, is also responsible for wet dog, sweaty horse and band-aid, among other unappetizing aromas and flavors.
“When you give people a bretty wine to smell, they associate it with France, and of course the French don’t like that,” says Linda Bisson, a professor of viticulture at the University of California at Davis. “They associate it with spoilage.”
Brett is a yeast that can grow in winery hoses, barrels, air vents — almost anywhere, even in a wine after bottling. It thrives on the phenolic compounds essential to red wines and does its dirty work after the beneficial yeast Saccharomyces has finished fermenting the grapes’ sugar into alcohol.
Brett has been vilified in modern winemaking since the 1950s, when it was first identified as a spoilage agent. UC-Davis, with its emphasis on winery hygiene and sanitation, has fought against various spoilers, including brett. Brett can be controlled by judicious use of sulfur dioxide during winemaking or eliminated by filtration before bottling. Many wineries guard against it by adding dimethyl dicarbonate, brand name Velcorin, a controversial chemical that can be toxic when undiluted but breaks down harmlessly in solution once added to wine.