To decant or not to decant? This question is not a simple one. For good clarets it's common, for Burgundies it's rare and for vintage Port it's a necessity. Decanting accomplishes two things; it aerates a wine, and if the wine has thrown a sediment, it leaves the sediment in the bottle and you have bright, clear wine in the decanter.

But you do need to be careful: many years ago I had a few bottles of 1949 Chateau Lanessan - a decent classed growth of a good vintage. 1949 was a good year for me too, it was the one in which I made first my appearance. I treated the wine as I treated all clarets and decanted it an hour or so before I wanted to drink it. As soon as it was poured, it died in the glass. All the remaining esters and aldehydes, those things that give a wine its distinctive bouquet and flavour had simply evaporated. An old wine still needs to be decanted, but it should be drunk almost immediately afterwards.

There are exceptions of course. Over the Millennium celebrations a friend opened a bottle of Chateau Latour 1945. That's a vintage that's still talked about; it was probably the best year of the last century. What made it so extraordinary a vintage was that it came at the end of Second World War, after a period of six years in which the Bordeaux vineyards had had less than their usual care. Despite its age, even after decanting, it still tasted like a mature, but not elderly, claret and still had a bright, garnet colour.

Increasingly red wines are being made for drinking young, but even a young wine can soften after decanting. Obviously reds that have been heavily oaked would benefit from decanting, but in general decanting helps to unlock many of the flavours in the wine - they 'open out'. You may have come across this phenomenon by accident. Sometimes a bottle of red can get left unfinished and unnoticed till the next day and often it will taste much better than it did shortly after opening. By being left at room temperature in a partially filled bottle, it was able to breathe and was effectively decanted.

Always check a decanter by smelling it before you decant a good wine into it. Make sure that there are no off-flavours or odours that would spoil the wine. Ideally decanters, like glasses, should be washed only in water as detergent residue does little to improve a wine.

Different grape varieties can make a wine open out at different speeds. If you're unsure it's a good idea to under-decant in terms of time, since a wine will continue to open out in the glass. If you over-decant there's always the risk. as with my Chateau Lanessan, that the wine will die in the glass and be nothing more than a flavourless red liquid. Be careful, too, that the room in which you leave your decanter to chambre isn't too warm. A good red that has been over-heated is unrecoverable, whereas one that is slightly too cool can still be warmed in the glass.

Wine of the Week.

Glen Ellen Sauvignon Blanc Reserve

Higher in alcohol than most whites at 13%, this Californian wine has a very fruity bouquet and taste. It's the sort of wine that's easy to drink without food, but could easily overpower a subtly flavoured dish. It would go well with pates, terrines or highly-seasoned foods.

Widely available, about £6.50