Wood Preservatives Blamed for Corky French Wines

Since the early 1980s, hundreds of French wineries, including some of the big names in Bordeaux, have been quietly renovating and rebuilding their cellars. While boom times have spurred much of the construction, many of the renovations were made for less salutary reasons: They were actually an effort to stem a worrisome increase in corky, musty-tasting wines.

The culprit many cite is chemically treated wood used for cellar construction, wine bottle bins and other purposes inside wineries. Though the problem has been well-known for years within the wine industry, it became more public following recent reports in the French press, including an investigative story in the French newsweekly L'Express. Wineries in other countries, including the United States, Spain and Australia, have also been affected, according to French sources.

The latest developments in France put a new wrinkle in the age-old debate over corky wines. What's not in doubt is the persistence of the problem. Wine Spectator calculates that 3 percent to 5 percent of the thousands of wines it reviews each year are corky, meaning that they have musty aromas and flavors reminiscent of wet cardboard.

While corks have long been blamed, some vintners in France and elsewhere believe that part of the problem may stem from conditions inside the cellar, due to the presence of a group of chemicals called polychlorophenols, particularly pentachlorophenol, which is applied to wood to protect it from mold and insects.

In Bordeaux, numerous chateaus have replaced roofs and walls in their wineries because the wood emitted polychlorophenol molecules into the air. Under the humid conditions in cellars, these chemicals can evolve into such contaminants as tetrachloroanisoles and pentachloroanisoles, which are similar to 2,4,6-trichloroanisole, or TCA, which is commonly cited as the substance primarily responsible for turning wines corky.

These contaminants, which pose no health hazard, can migrate into wine, according to influential French researcher and consultant Pascal Chatonnet, who runs a business in Bordeaux that helps vintners eradicate musty conditions from their cellars. Wines aging in barrel or in vats, corks stored in a cellar and even bottled wines have all been affected, Chatonnet explained. His findings have been backed up by various public and private research efforts in France.

It's difficult to estimate how widespread the problem really is. The Conseil Interprofessional du Vin de Bordeaux, a wine producers trade association, estimates that pentachlorophenol-affected cellars damaged less than 1 percent of Bordeaux wines. The CIVB tested 1,344 wines in 1998; all were Bordeaux wines bought in retail stores around France. Of the total, 44 tasted corky. Those found corky were then chemically analyzed, and 11 of them were definitively traced to anisoles from wood preservatives in cellars, while the rest were affected by their corks, said CIVB spokeswoman Sophie Girard. The organization would not reveal the names of the tainted wines.

The well-regarded Chateau Canon of St.-Emilion is one estate that suffered. The property's wine quality went down significantly from 1992 to 1995, with bottles often showing a dry and cardboard-like character when tasted. The problem was attributed to a chemical containing polychlorophenols that had been used to preserve the wooden roof of the building as well as the walls.

"It would have been completely ridiculous to hide your heads in the sand and not do anything," said John Kolasa, who oversees Canon, which is owned by the Wertheimer family. They bought Canon in 1995 knowing a problem existed. "We believed in the property," explained Kolasa. "So we did everything possible to correct the problem. We took out any source of pollution. We have done tests again, and it's all clean."

Many other top Bordeaux chateaus also took precautionary measures against polychloroanisoles, from testing for the chemicals in their cellars to replacing treated wooden structures. "This is an old story for Bordeaux at this stage," said Francois Thienpont, a wine merchant in Bordeaux whose family owns various chateaus in the region, including Le Pin and Vieux-Chateau-Certan. "My family had their cellars tested, and we never had the problem. But certain wooden parts of the cellar were replaced, to be sure. But this was done a few years ago."

New wineries seem to be hit harder than old ones, because the new materials have been recently treated with the chemicals by the wood suppliers. Air-conditioned cellars worsen the problem by speeding up the process of indoor pollution. In 1995, Domaine du Grand Vendeur in Chateauneuf-du-Pape told authorities that it had destroyed all its wine after a new cellar contaminated it.

In the United States, if this problem exists, it's hardly acknowledged. Christian Butzke, an enologist at the University of California at Davis and an expert on cork taints, said that he had never seen any evidence of California wine being spoiled by pentachlorophenol in wood preservatives, although he concedes that it could occur. Rather, he suggests that corks are the main culprit: "I would say that in 90 percent of the cases of tainted wine, the source is the cork, and it would be very difficult to argue otherwise."

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