David and Pat McGrath came home from England to establish their vineyard in the Blackwater Valley. Sheltered by the Knockmealdown Mountains, and from modest beginnings, they defied lack of sunshine and a cool Irish climate to produce what they regard as "pure Irish grape wine of the highest quality".

With a masterful ability to generate publicity, their company, West Waterford Vineyards near Cappoquin, is frequently mentioned on television and radio, as well as in magazines and newspapers (including The Irish Times).

The couple are presented as producers of "superb white wine. . .of the highest calibre". One exhortation is to "snap up the fine Reserve."

The existence of Irish wine is enough to send some into ecstatic adulation. But the results of scientific analysis commissioned by The Irish Times suggest the McGrath product is not all that it seems.

The McGraths put down roots in Waterford in 1989. They fought tenaciously against the vagaries of Irish weather, often putting appalling demands on themselves, as they attempted to make their enterprise viable.

That aside, declaring their wine to be "pure Irish grape wine of the highest quality", as stated on their brochures, is vehemently disputed by others who are vine experts and professional wine-tasters.

Yes, it is relatively easy to produce country wines made from the fruits of the hedgerow, or with apples and strawberries. It is a task at which the McGraths have shown themselves to be proficient.

However, to produce a high quality grape wine on an annual basis, according to wine experts who spoke to The Irish Times, is a wholly different proposition. It is, in their view, one next to impossible to fulfil under Irish conditions.

Mr David Llewellyn is a horticulturalist with an interest in growing grapes for wine production, particularly in Ireland. He has studied vine-growing, worked in Germany in the industry and is undertaking a postgraduate study at UCD on possible "micro-climates" in Ireland suitable for grape production.

A handful of people in the southern half of the country is attempting to grow grapes for wine production. He has contacted anyone he has become aware of, out of curiosity and research interest.

"I have always felt that the McGraths were reluctant to make themselves available to me since they became aware of both my interest and in particular, I suspect, my experience in vines," he claims.

Tim and Fiona York had their own vineyard south of Lismore, also in Co Waterford, up to the end of 1996. Yet they struggled to produce wine of significant quantity and quality growing Madelaine Angevine and Reichensteiner vines. Their vineyard is about five miles from the McGraths', on a slope overlooking the meandering Bride river - not unlike a typical French scene.

Mr Llewellyn believes the site is significantly superior for growing grapes to that of the McGraths. A south-facing slope with less frost and more sun ensures earlier flowering and a longer season.

"The Yorks were in a better location and yet struggling. It was perplexing. I wondered how the McGraths could appear to be so successful at a less suitable location for growing grapes and with a less suitable grape variety."

The Irish Times asked the Geisenheim Research Institute in Germany to investigate what was sold as the McGraths' 1996 Schonburger house wine. This was said by David McGrath in 1996 to be made primarily with Schon

burger grapes, but blended with a small quantity of other grapes grown at their vineyard (Madelaine Angevine, Seyval Blanc and Siegerebe).

There was nothing on the bottle label to differentiate this from other wine they were selling in June 1997, or to indicate its year.

A report by Dr Claus-Dieter Patz of Geisenheim's department of wine analysis and beverage research concluded that the McGrath product had "little to do with grape wine."

The comprehensive examination of the wine consisted, firstly, of a sensory evaluation (assessment of the wine by an expert panel by sight, smell and taste) and, secondly, chemical analysis in which tests were conducted for 21 different substances including sugars, acids and minerals.

The sensory analysis concluded that the taste was "very deviant" and "untypical". The aroma was "obtrusive". The sample had "not the least organoleptic resemblance - in terms of taste and smell - to a wine made from pressed grapes." The taste and odour were "more reminiscent of an apple or pear wine."

Some key elements of the chemical analysis supported the finding that "the investigated sample is by no means a typical wine produced from grapes."

Tartaric acid is a natural acid occurring almost exclusively in grapes, and ought to be present in grape wine. For this reason it is commonly tested for in wine laboratories in cases of suspected wine fraud.

The Geisenheim analysis of the McGrath grape wine found tartaric acid to be absent.

Mineral analysis also showed "noticeable peculiarities". The sodium content was "distinctly high" which, Dr Patz suggested, in combination with a high nitrate content might be due to the addition of water during the wine-making process.

Addition of water is a fraudulent practice, sometimes attempted to increase quantity. It is considered highly irregular and strictly forbidden in EU wine-producing regions, as elsewhere.

A European Commission spokesman confirmed that "addition of water [during grape wine-making] is absolutely forbidden under EU Regulation A22-87, which is applicable in all member states including Ireland."

Another key test carried out in wine laboratories in cases of suspected wine adulteration is measurement of the sorbitol content. Sorbitol is a substance naturally occurring at a relatively high level in fermented apple juice, but normally below 100 mg/litre in grape wine.

The Geisenheim analysis of the McGrath wine showed a sorbitol content of 1,600 mg/l, which was considered "noteworthy" by Dr Patz.

In the opinion of Mr Chris Foss, a lecturer in viticulture and wine making at Plumpton College, East Sussex, an absence of tartaric acid suggests a product was not made from grapes, or that the vines had succumbed to a very rare disease known as tourne.

If the latter applied, "the wine would be totally undrinkable." Asked about a high sorbitol level, he replied: "It suggests apples, apple concentrate or apple juice."

The Irish Times asked a professional wine taster, Mr T.P. Whelehan, wine critic for the paper from 1960 to 1988, to evaluate the same McGrath house wine. It sells at £4 per bottle. It had a distinct "appley taste", he said. "There is a foul finish to the wine. . .a quite nasty aftertaste coming from possible [presence of] sulphur, a cidery taste suggesting bad fermentation. There may be some grape [present] to justify the product."

Mr Whelehan tastes up to 4,000 wines a year and said this was among the worst he had tasted in 40 years.

Asked to evaluate McGrath's Reserve Schonburger", referred to by them as their "limited vintage", dated 1996 and selling at £10 per bottle, he said: "It tastes flat, oxidised, fruitless and has a strong malic acid taste, which could come from apples or very unripe grapes. There is an appley taste, too. It's pretty well undrinkable. I don't think that it is made purely from grapes."

Asked if the McGrath Reserve merited being classified as "pure Irish wine of the highest quality", he said he could not envisage under any circumstances that it would warrant such an appellation.

At the same sitting, he was asked to taste blind an English Schonburger wine.

Without seeing the label, Mr Whelehan said: "It has the look and smell of wine. It's a quite well-made wine, Germanic in style but not enough sharpness to be from there. It's a little thin, but I would respect that as something I would like. I would say it is German or a well-made British wine with a German grape."

It was a Tenterden 1991, an English table wine made by a leading British vigneron, using the Schonburger grape and selling at £4.75 sterling.

Mistakes were made in the course of wine-making, David and Pat McGrath admitted this week when confronted with the evidence about their produce. They said they deeply regretted this but insisted that all their wine-making was done "with good faith."

They had never wished deliberately to mislead people buying their wine.

On the results of the Geisenheim analysis, Mr David McGrath said that the product must have been "our apple and grape wine."

When it was pointed out that the purchaser on behalf of The Irish Times explicitly stated he wished to buy only grape wine and not any country wines (i.e. those containing other fruits), Mr McGrath accepted that he may have inadvertently sold the wine as grape wine.

"And God, am I sorry about that."

He claimed that all wines sold at £4 per bottle were in fact country wines and not table grape wine. When it was pointed out that the 1996 Bridgestone Guide to Ireland had referred to his grape wine selling at £4, he replied that he had not read that guide; this despite their publicity pamphlets saying the guide recommends their grape wines.

Mr McGrath admitted that some wine sold last year, notably their Schonburger flagship product, was "not up to snuff". It was "not equal" to what was on the table in the sense of "pure Irish grape wine of the highest quality".

He did not recall adding water to it, though he said it was possible he added a small amount. Where there was a gap at the top of a barrel, he may have topped it up with water to prevent an air gap.

They accepted that, given some of their premier 1996 wine was "nowhere near the mark", it was expensive at £10.

Asked to account for a distinct apple taste in this "limited vintage", he suggested that it might have been due to using unripe grapes. This, he added, "will not happen again".

To ensure that people get a high-quality grape wine in future, David McGrath said, he would sell his Schonburger only by the glass from the vineyard. He added: "We have learned a terribly hard lesson. We would do anything to redress what we have done."

The McGraths have been portrayed under media spotlights with the message that it is possible to produce significant quantities of quality Irish grape wine.

The appearance list is impressive: many RTE programmes including Nationwide, Live At Three, The Right Side and a full programme in the Video Diaries television series.

Beyond RTE, credits included the Financial Times, Farmer's Journal, the Examiner, a British TV holiday programme and a previous appearance in The Irish Times. The McGraths proudly promote themselves as "recommended by Best in Ireland 1996 Bridgestone Guide".

The Office of the Director of Consumer Affairs has confirmed that it has received a complaint about the wine. This, a spokesman said, "is the subject of investigation."