Cornell Food Scientists Are Helping To Uncork The Mystery Of 'Brett' Aroma In Wines

Scientists at Cornell University are starting to unravel the chemicalmysteries that produce the curious aroma found in fermented beverages likewine and beer. "We're trying to understand the aroma's chemical profile,essentially the aroma chemistry of the wine and the microbiology thatcreated it," says Jonathan Licker, a Cornell graduate student in foodscience.

Brett is the nickname for a wild yeast, "Brettanomyces." Winemakers oftenfind this yeast where they least want it: in barrels, production lines,bottled wine and even on the grapes themselves. Licker explains thatwithout proper sanitation, particularly after the harvesting of grapes,"Brettanomyces "can thrive in a winery. "It can become the unwelcome guestthat takes over your home," he says.

Licker, Terry Acree, Cornell professor of biochemistry, and ThomasHenick-Kling, Cornell associate professor of enology and microbiology, areusing a procedure known as gas chromatography-olfactometry to furtherunderstand the odor-active compounds found in wine. Christoph Egli, aCornell postdoctoral associate of molecular biology in Henick-Kling'slaboratory, is attempting to genetically differentiate and identify, usingDNA fingerprinting, the "Brettanomyces "strains. The researchers all workat Cornell's New York State Agricultural Experiment Station in Geneva.

"The chemistry of wine is very complex," says Licker, who has chemicallyanalyzed samples of domestic cabernet sauvignon from three different years,using the odor-analyzing methods developed at the Agricultural ExperimentStation. He initially found striking differences in chemical compositionin the samples provided by a winery from 1989, 1992 and 1994 batches. Theprofessional noses at the winery believed the 1989 sample was "bretty," the1992 sample was not too bretty and the 1994 sample was fruity and did nothave a bretty flavor.

The trained sensory snouts at the experiment station confirmed the resultswith a technical descriptive analysis of each wine. "The "Brettanomyces"yeasts isolated from the bottled wine were the same yeast strain within avintage, suggesting dominance of a particular yeast in a batch of wine,"Egli and Craig Mitrakul, who received an M.S. from Cornell in 1997, wrotein a recent research paper. The same yeast strain completely dominatedwines from the vintages of 1992 and 1994, suggesting that the yeasts tookhold in the cellar rather than in the vineyard, they wrote.

In the past, some brewers sought a bretty aroma for their beer, and evenwinemakers savored it during the early part of this century, but today theyeast is regarded as overwhelming in some wineries and the wine industry isconcerned that this wild yeast might be out of control.

"Our ultimate goal will be to provide winemakers with more tools to helpthem control and optimize brett aroma in their wine production," saysLicker. "You can still find brett in some of the best French Bordeaux anddomestic cabernet sauvignons. Many people -- winemakers and consumersalike -- think a little brett is a great thing."

Licker and Egli will present ""Brettanomyces:" Microbiology and Aromas,"at the New York Wine Industry Workshop, during the wine sensory workshop,"The Good, the Bad, and the Ugly -- a Review of Wine Aromas," Saturday,April 4, at the Geneva Lakefront Ramada Inn, Geneva.