You may have noticed a purple-and- green seal with a gold star winking at you from the label of a wine bottle in the past few days. If so, your eye has been caught, as intended, by the Institute of Masters of Wine's new Star of Excellence. Just over a week ago, at a grand tasting in London, the corks came out of the first 51 wines to win the accolade. Despite the quality of many of the wines on show, however, a row is brewing over what is seen by some as the thin end of a blatantly commercial - and eventually damaging - wedge.

Until the scheme was announced last May, the 39-year-old institute had always prided itself on its Olympian detachment from the world of commerce. In line with its policy of promoting the highest standards of wine education, it has been instrumental in organising seminars, courses and tutored wine tastings. The jewel in its crown is the Master of Wine examination itself, a tough test of practical and academic skills, passed by only 178 Masters of Wine alive today.

Success in the MW exam brings prestige and a passport to a high-powered job in the trade. Increasingly recognised abroad, the institute has in the past two or three years welcomed new Masters of Wine from the United States, Australia, New Zealand, South Africa, the Netherlands, Norway, Northern Ireland - even France. It has attracted sponsorship from, among others, Bollinger, Safeway, Sainsbury's and Australia's Rosemount. It was to finance its expanding activities without having to go cap in hand to sponsors that Colin Anderson, one of the institute's most respected members, dreamt up the Certificate of Excellence.

For pounds 50, a producer can submit a wine, which is tasted blind by a panel of seven Masters of Wine. The tastings are conducted according to the horrendously complicated rules of the Office International de la Vigne et du Vin (OIV). The panel is told the price, and takes into consideration value for money. A Certificate of Excellence goes to a wine receiving an average mark of 86 per cent (85 for a sparkling wine), which, according to the institute, 'is set at approximately the gold-medal standard of other wine competitions'.

The Certificate of Excellence entitles the successful producer to use the Star seal, at a cost of 3p a bottle. So a successful 10,000- case wine will yield the institute pounds 3,600 on top of the initial pounds 50 fee. That is where it hopes to make its money.

With pressure on to hand out certificates to commercial lines, the institute will have to take care to ensure the scheme is not seen as a licence to print money. But should it be dabbling at all in the world of commerce? Not according to some Masters of Wine. 'The institute is a non-profit-making body,' says David Molyneux Berry, who is also chairman of the International Wine & Spirit Competition. 'I've always understood it to represent its members and high standards in the industry. The only way it can make money is by selling lots of stickers. It then becomes a commercial operation. I don't think the institute should be involved in commercial operations. Sponsorship is quite adequate. And policing the scheme will be an impossibility.'

David Gleave, managing director of Winecellars, believes the scheme creates a conflict of interest. 'A high-quality educator should be impartial. We lose credibility and independence by throwing our hat into the commercial ring. By asking people to pay, the institute's name will be hijacked as a marketing tool. The institute should be more involved in seminars, tastings, exams and the MW magazine.'

Mr Anderson accepts that the scheme was devised to finance the education activities of the institute, but claims it is in line with its stated objective of 'promoting the highest standards of quality in wine'. Is the scheme, then, in the interests of the institute rather than the consumer? 'Twenty- five per cent in the interests of the institute,' replies Mr Anderson, 'and 25 per cent each in the interests of the consumer, the trade and the producer.'

On the evidence of the launch tasting, the operation of the scheme and choice of wines have been unexceptionable, although it is debatable whether gold stars have been awarded with absolute consistency.

There were some well-deserved 'golds' in the line-up, among them the Australian Coldstream Hills 1992 Chardonnay and Pinot Noir Reserve, and its 1991 Cabernet Merlot, Plantagenet's 1992 Chardonnay from Western Australia, and Villa Maria's fine 1991 Cabernet Sauvignon from New Zealand. Upholding the gold standard in France was a classic 1992 Vouvray Vieilles Vignes from Bourillon Dorleans; a richly concentrated 1990 red bordeaux, Chateau les Grands Chenes; Vacheron's archetypal 1992 Sancerre, Les Roches; and the 1991 Nuits St Georges Clos des Forets St Georges from Clos de l'Arlot.

Italy's 1990 Sassicaia was a star, if much too young to drink, as was the 1990 Forster Ungeheuer Riesling Spatlese from Deinhard. Graham's seductively sweet 1987 Late Bottled Vintage Port was worthy of its Certificate of Excellence.

Equally, there were wines that I would rate as no better than average. A couple of them received only bronze medals in last year's International Wine Challenge, and in addition I was struggling to place wines such as the 1992 Fortant de France Chardonnay, the 1990 Barton & Guestier St Julien, and the 1992 Chateau de Panisseau Bergerac Sec higher than bronze. As for the hideously expensive Batard-Montrachet from Moillard, it appeared to be showing signs of terminal oxidation.

Anomalies and questions remain. How is it, for instance, that one of the institute's sponsors, the Villa Maria group, has managed to garner four times the number of certificates awarded to Italy and Spain combined? (Villa Maria did not become a sponsor until after the awards were made, says Mr Anderson.) Do just three certificates between Italy, Germany and Spain inspire confidence in the scheme's ability to attract entries of the right calibre? How can the institute police the number of bottles legitimately entitled to the sticker? How can it control the price? Above all, can the institute avoid compromising its independence? 'The proof of the pudding will be in the eating,' says Mr Anderson.

Wines of the Week

A selection of recommended Star of Excellence wines:

1991 Philippe de Baudin Chardonnay, pounds 4.49 Waitrose, Gateway. Good value oak, spice and vanilla, with richly tropical, peachy fruit flavours.

1990 Cairanne, Cotes du Rhone Villages, pounds 4,75, Fullers; pounds 4.99, Waitrose (end April). From Max Aubert's Domaine de la Presidente near Ste Cecile les Vignes, a southern rhone redolent of spice, plum and red fruits, the extra maturity adding a smooth and rounded feel.

1990 Duque de Viseu, pounds 4.79, Safeway. A typically robust Portuguese red from Sogrape with fine plum and blackcurrant flavours and good length.

1992 Viognier, Fortant de France Collection, pounds 6.99, Thresher, Wine Rack, Bottoms Up. Intriguing floral scents and rich, full-bodied apricot fruitiness.

1992 Vouvray Vieilles Vignes, Domaine Bourillon Dorleans, pounds 6.90, Morris & Verdin, London SW1 (071-630 8888). If only all Vouvray were as good: magnificent floral, honeyed wine.

1990 Chateau les Grands Chenes, Medoc, pounds 9.75, Lay & Wheeler, Colchester. Quality claret from a fine vintage with seductive toasted oak nose and concentrated blackcurrant fruit.

1992 Coldstream Hills Chardonnay, pounds 7.99, Oddbins. Elegant, aromatic, with pineapple and melon fruitiness.

1991 Coldstream Hills Cabernet Merlot, pounds 8.95, Waitrose. Minty, ripe, succulent plum and blackcurrant fruit with fine, elegant tannins.

1987 Graham's Late Bottled Vintage Port, about pounds 10 from many off-licences. Floral, with sweet fruit flavours, like raisins in chocolate.