Half an hour before setting off for our family holiday in California earlier this month I took a package from a courier on my London doorstep to my kitchen, unwrapped four half- bottles of dark red wine that had three days previously been in barrels in various chateaux around Bordeaux, pulled the corks, wrote a tasting note for each on my laptop and published it on my website.

I had already been rung once by the sender of this package the previous day and twice that morning to check whether it had arrived. She urged me to taste them wines before I left since they wines were too fragile to last until my return. Such is the madness of the annual primeur campaign in Bordeaux, and the determination of château owners that their wines should be noticed.

Each spring thousands of us, merchants and commentators, descend on this city in south west France, virtually un-navigable for the next two years while a tram system is installed, to try to form an opinion on the quality and saleability of wines that will not even be blended and bottled for well over a year. What is it like to devote a week of your life focusing as precisely and intensely as possible on the embryonic wines of one region and one vintage?

I can tell you without hesitation that it is the most arduous task of my working life and one from which, without fail, I return less healthy than when I went. In fact because of it, the only time I have ever stayed at Venice's famous Hotel Cipriani I could summon up not a jot of enthusiasm for eating or drinking the whole time I was there. Which was a shame since this was a special surprise trip planned months in advance to celebrate Nick's half century.

Italy's major wine fair, Vinitaly in Verona, is conveniently timed immediately after the Bordeaux primeur tastings. More recently the Burgundians have devised a similar tasting jamboree just before. How anyone manages the grand slam - and they do, especially if crossing the Atlantic to Europe - I cannot imagine.

You might imagine I am crying wolf here. Could tasting wine possibly be anything other than pleasurable? The problem is partly the wine itself (tough, tart, inky, work in progress), partly the timing (first tasting appointments are at eight in the morning) and the sheer concentration required. Drinking is pleasure. Tasting is work.

Not that there is not immense intellectual stimulation involved. It truly is fascinating to see how each individual château performs each year and to try to build up an overall picture of the vintage - which is much more difficult than simply working out who, within a given appellation, has made the best wine. But hedonism it is not.

Anyone who has ever tasted red wines only a few months old but designed to live for years or decades knows that these wines very rarely provide sensual pleasure at the time. One is trying to read them for likely future development and potential. I am frequently asked exactly how to taste young wine and to go through the tannins, the undeveloped fruit and the acid to the process of assessment. But, like so many instinctive activities, breathing for example, it is now almost impossible for me to analyse and describe it. The best I can do is say we are generally looking for the right sort of balance between all these elements, as well of course as attractive flavours.

But what of the mechanics? Well the micro-mechanics are that a head cold is unhelpful. I completed the 2000 primeur marathon with a real stinker and had to rely heavily on nasal decongestant spray, taken long enough before tasting that the residual flavour was not a distraction.

It goes without saying that spitting is essential - particularly since we sometimes taste 100 wines in a day. And, unless you have the memory of France's wine guru Michel Bettane, some efficient form of note-taking is also required - even if the handwriting does tend to deteriorate a bit towards the evening.

The typical tasting is of a range of different wines from the same appellation(s) held at one of Bordeaux's hundreds of wine châteaux where the converging cars are marshalled into some suitable paddock, the tasters crunch over the gravel to a well-signposted salon, grab a rather fine long-stemmed glass and then fight their way to the bottles of wine taken recently from barrels before fighting their way to a spittoon, all the while writing their notes in notebooks and on clipboards with mouths too full to chatter.

As the day wears on our teeth and fingers blacken and, such is the physiognomy and practice of some tasters, that they develop little purple wings on each side of the lips where the glass hits the cheek.

If all this sounds a little spoon-fed, you should be aware that there are complications. The Union des Grands Crus organises, splendidly, the major appellation tastings but the truly significant wines, the so-called first growths, refuse to have their wines seen off the premises at these bun fights so the tasters have to trek, in a series of carefully synchronised appointments, to each in turn. And since the UGC tastings are not grand enough for the first growths there are, inevitably, other châteaux owners who believe they too should operate outside the system. So, all in all, an appointment is required at about two dozen châteaux, not to mention invaluable supplementary ranges of wines on show chez merchants in and around the city providing a useful second or third look at many of these wines, plus what is now a positive rash of tastings of less exalted but often particularly interesting wines outside the remit of the UGC.

Thanks to a campaign mounted some years ago by Michel Bettane, the UGC tastings for journalists are now hugely more valuable and peaceful than they were. We now have the option of tasting blind which is a boon in eradicating any possible prejudice for or against particular châteaux, and these blind tastings tend to be held, seated, in conditions of silence disturbed only by the click of our keyboards. Indeed at the end of every March nowadays there must be a run on multi-plug adaptors as the blind tasting salons are equipped. Some of them even treat us to servers - true luxury.

One infallible rule of wine tasting is that it makes you terribly hungry, so what of the solid matter? Rather good lunches have generally been provided by the châteaux holding UGC tastings to set us up for an afternoon's tasting but this year a diktat went out that lunches should be lighter. Some châteaux interpreted this by omitting the cheese course and moving straight on to strawberry parfait, one by serving canapes only. The French journalists' reaction to this is not recorded.

In past years I have tended to socialise in the evening, enjoying dinners with Bordeaux's incomparable mature wines - the reason, after all, we are all here in the first place. This, I have finally worked out, has doubtless been my undoing, so this year I communed instead with salad and cheese from room service. It did not provide quite the same input of gossip but is probably responsible for the fact that only serious damage I seem to have done this year is to my teeth.

I took advice from an Australian wine judge-cum-dentist and armed myself with Gel-Kam, a mineralising gel applied to the teeth each evening designed to ward off the predations of acid. But those 2003s sure were deep in colour, as I can tell every time I look in the mirror.