I got an email this week from a reader who asked a seemingly simple question. She'd bought a New World Cabernet Sauvignon 1998 from a supermarket, which turned out to be corked. The supermarket made a refund, so in that respect all was well. However she'd noticed that on the back label it read 'a wine that is at its best after three years' and she wondered why then was it on sale at all. After all, by this reckoning it's apparently already past its best. Or is it?

When it comes to wine nothing happens quickly. The ageing process, by which tiny amounts of oxidisation happen each year, changes the wine's character. In a red the acids and the tannins soften, the colour slowly changes from a dark purple to a brick red, the flavours blend into a more complex combination. Depending on how the wine was made that process could take anywhere from five to fifty years. It's the wine-maker's choice: he can make a wine that's ready to drink in few weeks, like a new Beaujolais, but that will be undrinkable in a year, or he can make a wine that can't even be approached for five years, but that will last for perhaps fifty years or more. It's a decision that's dictated by how much tannin there is in the wine, and that depends on how the wine is marketed; whether it's for immediate consumption or for laying down.

No matter which approach is taken, the wine will age in the same way. It will be undrinkable at first, then it will approach its peak, then it will plateau, then it will deteriorate to the point of being undrinkable. Notice, though, that there's a plateau stage; a stage at which the wine holds. So to go back to the original question, the answer is that the wine will be at its best after three years, and may well remain at that stage for another five before the ageing process makes its presence felt. It's not like milk - once it's past its best before date it's unfit for consumption - rather it's saying that you really shouldn't drink it before three years have elapsed. The wine, in the maker's opinion, is mature at three years and not before. It doesn't mean you have to drink it in its third year. It's perfectly likely that it will taste better at five years of age than it did at three, since the original question referred to a Cabernet Sauvignon, the grape that most of the world's long-lived wines are made of.

Wine of the Week

Ramos-Pinto 'Aperitivo' White Port

As ever championing the underdog, let me suggest as warm days approach, a drink with a difference. White port has long been drunk in Portugal as an aperitif, but is relatively unknown here. Take it chilled in a long glass with ice and soda as a refreshing summer drink.

Fairly widely distributed, RRP €17.25