Bordeaux plays host next week to the world's fine wine trade who descend en masse to sniff, sip and spit their way through the 2014 vintage.

The grandest chateaux on earth will fling open their doors and pour for free wines that can cost hundreds of pounds. It sounds like heaven, but there's a catch. Barely six months old and drawn from the barrel, these wines are raw in the extreme.

"It's always been slightly ridiculous," admits Gary Boom MD of Bordeaux Index. "It is really difficult to taste wines that young, but you can do it and judge them. An old hand taught me to forget everything else and just look for the balance between fruit and tannin. Of course it would be way better if it were postponed for a year, but it's not going to happen."

The system, known as 'en primeur', works brilliantly for the grandees of Bordeaux. Following the tastings, they gingerly release their prices, each looking over the other's shoulder to make sure they are charging enough. If all goes well they can sell their entire production in an afternoon and sit back as their wine mellows in the cellar. Meanwhile its ownership flips from broker to négociant (merchant), to well-healed wine lover often via a speculator if we're talking 'investment-grade wine' to use an ugly expression.

For those in the whisky trade the idea of selling a year's output in just a few phone calls before it is even legally whisky is the stuff of fairy tales, but that's effectively what happens in Bordeaux. However with 'en primeur' the wheels may be coming off.

"The reason it's sort of broken, is that some of the chateaux have got quite greedy," says Corney & Barrow's fine wine director Will Hargrove. The reason for buying en primeur and paying money up front, he would have told his private clients, is that you will never be offered the wines at a better price. In many cases that has patently been untrue for the last three or four years.

At this year's Bordeaux bun fight one face will be absent - that of the all-powerful American critic Robert Parker whose scores out of 100 could make or break a chateau. Those speculating in wine who imbibed his every word were shocked to hear his latest pronouncement: "For 37 years, I've thought wine was a terrible investment."