It happens occasionally to all wine-drinkers; you open a bottle and find the wine is 'corked'. It's an unmistakable taste, once you've encountered it, you'll know it the next time. It's a taste that has been variously described as woody or earthy. Wine that is 'corked' has an aroma that matches the taste - that same woodiness comes through in the bouquet.

At a rough estimate you can expect to find one bottle in 30 to be corked. Why this happens is because the cork in the bottle is an organic product - it's made from the bark of the cork oak, a tree that covers millions of acres in central Spain. Being an organic product, it's variable, so before it can be used to make a stopper for a bottle of wine it has to be processed. It's in the processing that the problem is thought to occur. During the washing process it seems that a fungal cross-infection reacts with a steriliser in the wash, which produces a third product that creates the 'corked' taste. If a wine is stoppered with one of these corks, it begins to acquire the flavour from it.

Like the transition from wine to vinegar, the transition from wine to corked wine is a long process. Just as a wine might exhibit the first tiny hints of vinegar long before it actually becomes vinegar, a wine that is corked may easily be missed when it's at the start of the process of becoming corked. Frequently I've found myself almost at the end of a glass of wine before the corked flavours make themselves felt. Sometimes of course, at the other end of the spectrum, the odour of corked wine is so strong at the instant of uncorking, that you know at once.

Constant research into the chemistry of the cork and its production means that the incidence of corked wine is less than it used to be, yet it still occurs. The reason why we go through the little ritual in restaurants of tasting the wine first is not to see whether you like it or not - it's assumed that if you ordered it, you like it - but it's rather to give you the opportunity to return a wine that's corked. Smelling the wine prior to tasting it will also give you the opportunity to avoid tasting a corked wine if you can catch it on the nose first.

Wine of the Week

Saint Chinian 1999 'Les Garriguettes', Gerard Bertrand.

If you like huge reds, bursting with fruit and flavour, then this wine will fit the bill. Made from a blend of Syrah, Grenache and Cinsault, the hot summers of the Languedoc ensure the very ripe grapes that produce this wine. It's powerful enough to hold its own even with a dish like chilli con carne.

Available O'Briens off-licenses, RRP £8.99.