The scene was a large London trade tasting at the Merchant Taylor's Hall: Bordeaux '88s, so far as I remember. I was a greenhorn, sharing my tentative impressions with a coterie of newly acquired and vastly more experienced wine-writing colleagues. Did I like the wines? Fairly, I said. I quite liked their austerity. One of my seniors, I recall, pounced on this word like a cat on a hapless vole. "Austerity?," he said. "You mean thinness? Exaggerated acidity? That delicious dilution? That wonderful rawness of flavour?" He warmed to his task, as the cat might paw the half-dead, maimed vole around the lawn for the pleasure of watching its doomed attempts at escape. "You mean the fact that in five years all these wines will provide the same kind of pleasure as a cold shower?

Ah yes, where would Bordeaux be without its austerity? Don't we just love a dose of chilliness, a bit of boniness, the eternal cold shoulder? Who wants pleasure in a wine, after all? Especially an expensive wine. That would be ridiculous. Obviously the only reason we drink a vastly overpriced wine made by an aristocrat in a suit in a château is to be beaten up by it. Yes, I quite agree with you. Lovely austerity; lovely."

It was, as you might imagine, a while before I used the word with any sort of approbative gloss again. Fifteen years, to be precise. Until today.

Well, times have changed, after all. We've got Parker, Rolland and the pleasure revolution. We've got global warming and garagistes. You'd have a job finding a bony Bordeaux nowadays; the one thing they all promise is pneumatic bliss. Chile, Argentina, the New Spain, all those old-vine Aussie Shirazes: our best bottles nowadays could model for Rubens or Titian.

Not that my subject is Bordeaux; it's Chianti. That mortifying memory was dredged up by fifteen minutes spent enumerating to myself everything I love about Chianti. And a measure of austerity is one of those things. Great Chianti is like a walk in an olive grove by moonlight: it's a wine of pale light and dark shadows. There should be a sour quality to its acidity; you should feel the snap of vulpine jaws when its tannins meet your tongue. Sangiovese grown in galestro leaves a stony trace.

It's laurel and coffee; it's complicated plot-lines; it's a whisper in a courtyard. You wouldn't necessarily like the first sip. You need to take it to table, give it air, pass time with it. If any wine could be said to be Old Europe in a glass, it's Chianti. It's wonderfully, elegantly, satisfyingly austere. I've never liked it more than I do today. I may very well drink little else in twenty years. Were it not for the fact that more and more of it is polluted.

I didn't really notice at first; my mind was elsewhere. It's been tastings over the last year or two that have sent me back to the text books, and they have corroborated what my papillae have been reporting: that Chianti isn't fully Chianti any more. Since 2000, producers have been able to add up to 20 per cent Cabernet, or Merlot, or Syrah (or other recommended and authorised grapes).

Not all do, of course, and I've now taken to scrutinising back labels and information sheets so that I can weed out the corrupted. But my amazement hasn't faded. I still can't believe that the growers of the region are happy for bottles of DOCG Chianti Classico to set off for market with a great dollop of Cabernet or Merlot or Syrah inside them. Blends of this sort just don't taste like Chianti any more: they're fuller, richer, fruitier … less deliciously austere. They may, of course, be very good wine - but isn't that why IGT Toscana exists?

What is the point of troubling to put whatever-you-want blends into some sort of legal and regional framework if you then surrender the meaning of the very name from which those other wines have been so carefully differentiated? 'Chianti' was first used in 1398, cited (as a white wine) in the copious correspondence of Francesco di Marco Datini, and growers (including Grand Duke Cosimo III in 1716, Cosimo Villifranchi in 1773 and Baron Bettino Ricasoli in 1872) have been struggling to endow it and enrich it with meaning ever since. This decision dilutes that meaning pointlessly, internationalising and homogenising one of Italy's greatest treasures.

And I hope the French are listening. France's current wine crisis has loosed a torrent of largely superficial criticism of its AOC system, with sheep-like commentators tumbling over each other in calling for whatever-you-want blends to replace the 'rigid' AOC rules which 'stifle creativity'. Learn from Chianti's mistake, chers amis. Keep AOC wines as true as you can to the sensorial ideal which gave rise to them in the first place, no matter how difficult or unfashionable, and leave Vins de Pays for all that unimaginative, internationalised, uncreative 'creativity' for which an ephemeral market exists.