Wine-growers and brewers, often hopeless at describing their products on the label, have much for which to thank supermarkets and high-street shops. Now whisky distillers can add their gratitude.

For years, shops have displayed cards describing the flavours of wines and grading them according to dryness and sweetness; now Safeway is doing the same for Scotch. "Our research showed us that some customers were interested in trying different whiskies but did not know which would suit their taste," explains Jim Rands, marketing controller for Safeway.

It is not easy with wines: how do you code a chardonnay that has both sugary syrup and tannic dryness? It is even more difficult with Scotches, most of which combine malty sweetness and at least some peaty smokiness.

Fearing that a scale of dryness and sweetness would be simplistic and inaccurate, Safeway has opted for degrees of intensity. These are explained in a notebook attached to the Scotch shelves in the supermarket.

A little-known blend called Glen Nevis is dubbed a one-point whisk: "lively, fresh ..." Safeway's own-label blend merits two points: "clean, with a hint of peat". The Famous Grouse gets three: "ripe, fruity, smooth, sherryish". Four points to Teachers: "dry, nutty, spicy and peaty". The only five-point blend is Johnnie Walker Black: "big flavours, rich, smooth, silky..." Scores do not indicate quality. Some customers may prefer the light touch and delicacy of a one-point whisky to the weight of a high-five bruiser.

In the case of malt whiskies, Safeway has worked even harder to recognise the complexity of the products. While a one-point malt promises to be "light and delicate", a two should be "flowery and aromatic", and three "malty and honeyed". Four points suggests a "spicy and warming" whisky and five, a dram that is "powerful, pungent and intense".

The world's biggest-selling malt, Glenfiddich, wins a one: "salty, crisp, refreshing". The Glenlivet scores two: "citrussy, floral". Oban, with its "liquorice note", gets three. The "nutty" Cragganmore is judged a four. Lagavulin has five: "powerful, peppery, leathery".

Who decided upon these scores and descriptions? In the world of wine writing, with so many voices, it might be easy to establish a consensus. Whisky has its bards, but they are fewer. Safeway decided to consult the blenders working for the biggest producers of Scotch. These are remarkable men.

A well-known Scotch such as Ballantines, Bells, Grouse or Whyte & Mackay might be blended from as many as 30 or 40 malts and two or three grain whiskies. In the original combination, established decades ago, the blender has to maintain the same character in the end product despite changes in the malts and grain whiskies available to him. These changes are in every cask of whisky arriving for the attention of the blender.

Occasionally, new distilleries are established. More often, old ones close - and sometimes reopen. From a single distillery, each batch of whisky will taste slightly different. Each season's will be affected by weather and by the barley harvest. Old varieties of barley are replaced by new ones that are more resistant to disease or weather, or provide a better yield of grain or fermentable sugars. When the English drank a lot of sherry, the empty butts and hogsheads, often made from Spanish oak, went to Scottish distilleries; now, much whisky is matured in former Bourbon barrels, made from American oak.

What did the cask previously contain? How many times has it held whisky? For how many years? These factors greatly influence the character of the mature whisky. If a distillery has six warehouses in which to age its whisky, each will produce slightly different aromas and flavours. Even casks from opposite corners of the same warehouse will vary in character.

From every cask of whisky a sample is sent to the blender, who pours it into a "nosing" glass. This is shaped like a sherry copita, to retain the aroma. The blender primarily uses his nose - he does not usually taste the whisky. He then orchestrates the casks to ensure that his company's blends remain consistent to the character required. The same company may make blends under a variety of brand names for different markets, or a selection of ages or price ranges, and each has its own character.

Blenders have astonishingly reliable noses, and a good vocabulary of aroma and flavour but, like most people in the drinks industry, they are as sensitive to defects as they are to the merits of their products. A blender is as likely to declare a whisky "cat pee" as "flowering currant". Because he is trained to make well-balanced blends, he may also be wary of the pungent whiskies so loved by a growing band of connoisseurs.

Would blenders come up with negative-sounding descriptions, especially in the case of very powerful whiskies? Worse still, would they be tempted to dismiss each other's blends? Safeway, concerned on both counts, invited me to the grading session as a sort of United Nations observer, from England.

We met in the middle of Scotland, in a distillery that was not to be featured by Safeway. Never before had these blenders appraised each other's produce face to face. At first, the encounter was statesmanlike, but these generally taciturn men gradually became more loquacious. Faced with Safeway's Five- Year-Old, Richard Paterson (who blends Whyte & Mackay, among others) commented favourably on its soft-fruit flavours. Some of his contemporaries thought there was far too much butterscotch. I found an attractively tea-like character.

There was dissent over Claymore, with one taster pronouncing: "Sugar water!" Glen Nevis won praise for its heathery flavours from Ian Grieve (of Bells). A half-forgotten blend, VAT 69, was welcomed back by Robert Hicks (Ballantines), who deemed it "a definite three". The floral Langs was judged to be "resiny" by John Ramsey, The Famous Grouse taster. His own blend aroused a long, and generally very favourable, discussion, as did Mackinlays.

When another blender's own product attracted more perfunctory respect, he felt obliged to explain, with some eloquence, its virtues to his peers.

It is one thing to know your own product, but what of the rest? When the malts emerged, the blenders were able to identify almost every one. I was not surprised when I picked out Glenfiddich and the volcanic Talisker, but pleased to spot the minty, cakey, Glen Ord, and the complex Cragganmore.

Of the malts, Glenmorangie was drier and flintier than I remembered its being, and I learned just how much I enjoy the tar-like Caol Ila. I wish more of the tasters' spicy responses had made it into the stores. The "coriander" in the Glenlivet, the "cinnamon" in Glenkinchie, and the "fruit cake" in Glen Ord should give all three an occasional place at the dining table, as aperitif, accompaniment or digestif.

Is it really true then, as devotees insist, that Scotch is appropriate on any occasion? With such a wide range of flavours, identified by Safeway, why ever not?