Why does wine sometimes cork

A.� If you've opened a bottle of wine to discover it smells like a musty old hymn book, it's the chemical compound called 2,4,6-trichloranisole. TCA, as it's known in spitting circles, is responsible for corked wines. These have nothing to do with bits of cork floating on the surface.

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All sorts of things can go wrong with a bottle of wine, from explosion to bacterial spoilage, but the most common fault is cork taint. Anything between one and 10 per cent of wines are corked. The problem with establishing a reliable figure is that "corkiness" varies in intensity. In the most extreme cases, it renders the wine undrinkable, though not physically dangerous; in others, it just flattens the aromas and flavours.

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Q.� Where does TCA come from

A.� Nobody really knows. The Oxford Companion to Wine suggests it's "caused by the action of chlorine on cork bark or wood" during manufacture of corks, but efforts to eliminate it have met with only partial success. Most cork manufacturers have stopped using chlorine to bleach their corks, but the problem hasn't gone away. Some argue that the taint can come from barrels or winery rafters as well as corks, and the image of natural cork has suffered in recent years. The Portuguese Cork Association, APCOR, has launched a charm offensive in the UK.

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Q.� It's not just cheap wine that's affected is it

A.� TCA is a random taint, which can affect the finest chateau-bottled Bordeaux as easily as the cheapest plonk, although the problem is less prevalent in most expensive wines. If you buy a bottle of wine that's corked, it should be taken back immediately.

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Q.� What about plastic tops

A.� Roughly eight per cent of all wines are now screwcaps or plastic stoppers. These have helped eliminate the risk of cork taint in many inexpensive wines. Plastic corks and screwcaps can be difficult to remove and are often associated with basic Lambrusco, which has made producers wary of switching too quickly, particularly for their best wines.

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Last year, Plump Jack, a Californian producer released a Napa Valley Cabernet Sauvignon with a screwcap at more than $100 and many wineries in Australia's Clare Valley and in New Zealand switched to screwcaps for some or all of their production.

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By Katharine MacColl

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