Taking the Barnyard Out of Your Wine

Scientists are decoding the brettanomyces DNA to stop wine spoilage
Aug 7, 2009

The only thing worse than that first whiff of barnyard smell coming from your glass of wine is the realization that the whole case is contaminated. Brettanomyces, aka brett, can be a winemaker's worst enemy. A yeast species that contaminates wine and corrupts the entire fermentation process, brettanomyces can lead to flavors best described as sweaty horse, manure, Band-Aid and burnt plastic. At lower levels, some find it pleasantly spicy, with cedar and earth undertones. But higher concentrations ruin a wine completely.

Now, scientists have begun a project to decode and sequence the brettanomyces genome. They hope that a better understanding of the yeast's genes will help in the prevention of future contaminations, or perhaps even turn the now-troublesome yeast into a positive addition.

"Contamination is a major problem in the wine industry," said Trevor Phister, an assistant professor of food, bioprocessing and nutrition at North Carolina State University and lead scientist on the project. "The better we understand the metabolism of the organism, the better we can understand how the yeast is surviving, and that will point us in the direction of eradication."

For winemakers, brettanomyces can be a devilish opponent. It can lurk in certain vineyards, flourishing on grape skins. Or it can contaminate a winery, finding a happy home in old barrels. The yeast itself cannot be smelled or tasted in wine; the unpleasant aromas and flavors result from certain compounds associated with brett, especially 4-ethylphenol (4-EP) and 4-ethylguaiacol (4-EG). Once these two chemicals are produced during fermentation, they combine with other elements in the wine to produce the off tastes and odors. Until recently, vintners' best diagnostic option was to perform tests to measure for 4-EP and 4-EG. But no technique currently exists to remove the compounds.

According to Phister, the reason brettanomyces is so hard to eliminate is that the yeast evolved to survive the world of microbial combat. Within fermentation tanks, yeast and bacteria fight over space and resources. When fermentation goes smoothly, saccharomyces, the yeast used to make wine, wins the battle.

But brettanomyces is a cagey opponent. While other organisms waste energy fighting each other, brettanomyces waits for saccharomyces to kill the competition. Then, often when wine is transferred to barrels for aging, the brettanomyces strikes, overtaking the saccharomyces.

Wineries have tried a number of different chemical mixtures to ward off infection, but none have proven fully effective. Phister believes the genome will provide answers on how brettanomyces survives the initial battle with saccharomyces, how it spreads so fast and, ultimately, on how to stop it.

To decode the brettanomyces genome, Phister will work with the Department of Energy's (DOE) Joint Genome Institute. The seemingly incongruous pairing of the Energy Department and winemaking stems from problems with brett contamination in biofuel production. Biofuel producers use saccharomyces to convert organic waste into ethanol fuel. In 2008, brettanomyces eradicated and replaced over 2,000 pounds of saccharomyces in an ethanol production plant in just a few weeks.

Of course, some scientists warn that decoding the genome won't produce answers right away. "It's not going to be easy, and I'm skeptical it will lead to the brettanomyces solution for a number years," said Kevin Verstrepen, a yeast genetics and fermentation researcher at Katholieke Universiteit in Leuven, Belgium. "Over the long term, though, its probably one of our best hopes for controlling it."

And once winemakers can control bretannomyces, they may even be able to use it to their advantage. For some wines, a little brettanomyces actually adds body and complexity. The current inability to control brettanomyces has doomed every attempt to deliberately introduce it to winemaking. But if Phister's project produces a method for controlling the yeast, some vintners may forgo eradication and utilize this currently maligned yeast to produce some new and interesting wines.

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