For years, wine fans have raged against TCA, the chemical compound blamed for corked wine. Cork producers have tried to eliminate it and wineries have switched to screw caps and other stoppers to avoid it. But TCA, or 2,4,6-trichloroanisole, is not the only cause of moldy, earthy, wet cardboard aromas in your wine. Since 2004, scientists have known of another compound—MDMP, or 2-methyoxy-3,5-dimethylpyrazine—that can leach out of corks and into wine, but they haven’t understood where it comes from.
Now they’ve found the culprit. A group of scientists, led by Dr. Pascal Chatonnet, at the Excell Laboratory in Bordeaux, have isolated a bacteria found in soils, plant roots and bark. When cork bark is used to create stoppers, the bacterium can produce MDMP and contaminate the wine. The bacterium can also be found in oak chips, staves and barrels used to age wine, another potential source of contamination.
“MDMP and its particular odor have been identified in some wines,” said Chatonnet, a sensory scientist and founder of Excell Laboratory. “There’s a presence [of MDMP] in quite a high percentage of basic new cork stoppers and also in basic oak alternatives, mainly untoasted, which is the new fashion.”
The researchers looked at corks from five suppliers in Portugal, detecting MDMP in 86 percent of the batches. While the smallest amounts of MDMP present little to no risk of significant contamination, the researchers explained in the study that 51.2 percent of the corks represent a more serious risk and 16.3 percent have an extreme risk to wine.
The study also examined the use of oak chips to add flavors to wine, following a producer in the Languedoc region of France. The researchers tested wine from three vats of Syrah and Grenache, two of which were treated with slightly toasted wood chips. The testing was run before the wine came in contact with cork. Chatonnet’s team found that both vats using wood chips were contaminated with MDMP.
Chatonnet’s previous research has provoked some controversy. In a study published earlier this year, he argued that oak barrels are a more common source of TCA contamination than suspected. The findings angered French coopers, who accused Chatonnet of inventing a problem to sell his diagnostic tests.
When it comes to MDMP, Chatonnet believes that one problem spot for barrels and wood chips is light toasting. Studies of the thermal treatment of oak showed that wood quickly toasted at temperatures of at least 437 degrees Fahrenheit for 10 minutes reduced MDMP content by 93 percent. “With barrel alternatives like staves and chips, the range of toasting levels is higher,” Chatonnet said. “Untoasted products are used more and more. These products could be responsible for MDMP in wine.”
Chatonnet explained that this research offers winemakers a new point of view of off-odors typically blamed on TCA. He hopes it will spur investigation of the efficiency of various cork-making technology and decontamination processes.
John A Edie — Bethesda, MD — March 15, 2011 4:02pm ET
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