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Dear Dr. Vinny,

Since TCA is a chlorine-based organic compound, and no one uses chlorine in winemaking, storage or in the cork-production process anymore, why hasn't it been eradicated in cork-closed wines?

—Alan, Metairie, La.

Dear Alan,

If it were only that simple! The chemical compound 2,4,6-trichloroanisole (TCA for short) has long been the primary culprit behind cork-tainted, or "corked," wines. You’re right that this organic compound is created by the intersection of chlorine and plant phenols—the plants in the wine equation can be cork, but it can originate from other types of wood like barrels and pallets.

You're right that most wineries and cork-production facilities have phased out chlorine-based cleaning products and sanitizers—these days peroxide- or ozone-based cleaning routines are the norm. But TCA is still around. Chlorine-based pesticides used to be sprayed on cork trees, and it takes a decade or longer for a cork tree to regenerate its bark. There can also be chlorine in local tap water, and TCA can linger in equipment like hoses and filters and other components. The recent news is that talented (and cute!) dogs are now sniffing out TCA in wineries.

Even though it’s the primary source, TCA is not the only cause of musty notes in wine. There are other compounds, like tribromoanisole (TBA), which usually comes from wood preservatives and flame-retardant paints used in cellar construction, and there is concern that it can be airborne. TBA can also attach to polyethylene-based winemaking equipment (like silicon bungs that seal barrels). And then there is MDMP, or 2-methoxy-3,5-dimethylpyrazine, a compound that can be produced by a bacteria found in soils, plant roots and bark, which also causes musty notes. MDMP has been found in oak barrels, staves and chips that are used to make wine.

However, the cork and wine industries have invested many millions of dollars in eliminating TCA over the past decade and more, and we have found that incidences of cork taint are generally on the decline in our own official Wine Spectator blind tastings.

—Dr. Vinny

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