Classification of Single Malt Whiskies 

Clussification by clustering, cartoon from the Scotch Malt Whisky Society 

"If I like a particular malt whisky, what other whiskies might I also enjoy?"

A classification of single malt whiskies has been developed which attempts to answer this question.  It has been presented at several scientific meetings and has been published.  Following consultation of industry interests, the results were reviewed and were published as "Whisky Classified 2000" in April 2000.  It is now available as a book "Whisky Classified: Choosing Single Malts by Flavour".

Tasting notes in 10 recently published books on malt whisky were analyzed for 86 readily available single malt whiskies (Arthur (1997), Broom (1998), Jackson (1995), Lerner (1997), MacLean (1997), Milroy (1995), Murray (1997), Nown (1997), Shaw (1997) and Tucek and Lamond (1997)).  Tasting notes published by the distilleries were also reviewed, where available.

Most distilleries produce several brands that are differentiated by length of time in cask, special conditioning or finishing, e.g. to impart flavours such as oak, sherry, port or Madeira to the whisky. As our objective was to develop a classification of malts that are readily available to consumers, we felt we should select a benchmark malt whisky from each distillery.  We firstly excluded rare malts and any premium brands that are specially aged, cask conditioned or finished.  We also decided not to cover distilleries that had been demolished or are not currently in production.

Not all of our 10 authors reviewed the same distillation from each distillery, as some limit their tasting notes to house style only (e.g. Milroy (1995)).  Where more than one distillation is produced we selected the most widely available brand, usually of 10-15 years maturation in cask.  New distilleries that currently offer young malts (Arran and Drumguish) were included for future reference, as they evolve. Vatted malts (blends of pure malts), and malt whiskies produced in Ireland, Japan, New Zealand and Wales were excluded.  We thus arrived at 86 single malt whiskies of around 10-15 years maturation, most of which are widely available in the U.K.

Six single malts that illustrate the rangeA vocabulary of 500 aromatic and taste descriptors was thus compiled from the tasting notes in the 8 books.  These were grouped into 12 broad aromatic features: Body (Light-Heavy), Sweetness (Dry-Sweet), Smoky (Peaty), Medicinal (Salty), Feinty (Sulphury), Honey (Vanilla), Spicy (Woody), Winey (Sherry), Nutty (Oaky-Creamy), Malty (Cerealy), Fruity (Estery) and Floral (Herbal).

The 86 single malts were classified using ClustanGraphics.  The cluster analysis groups malts into the same cluster when they have broadly the same taste characteristics across all 12 sensory variables.  Technically, the method minimizes the variance within clusters and maximizes the variance between clusters.  The analysis was completed using FocalPoint Clustering within ClustanGraphics on a standard PC.  The result was ten clusters of single malt whiskies, as in the following table.

Classification of Single Malt Whiskies

Cluster A ( Full-Bodied, Medium-Sweet, Pronounced Sherry with Fruity, Spicy, Malty Notes and Nutty, Smoky Hints): Balmenach, Dailuaine, Dalmore, Glendronach, Macallan, Mortlach, Royal Lochnagar;

Cluster B ( Medium-Bodied, Medium-Sweet, with Nutty, Malty, Floral, Honey and Fruity Notes): Aberfeldy, Aberlour, Ben Nevis, Benrinnes, Benromach, Blair Athol, Cragganmore, Edradour, Glenfarclas, Glenturret, Knockando, Longmorn, Scapa, Strathisla;

Cluster C (Medium-Bodied, Medium-Sweet, with Fruity, Floral, Honey, Malty Notes and Spicy Hints ): Balvenie, Benriach, Dalwhinnie, Glendullan, Glen Elgin, Glenlivet, Glen Ord, Linkwood, Royal Brackla;

Cluster D (Light, Medium-Sweet, Low or No Peat, with Fruity, Floral, Malty Notes and Nutty Hints ): An Cnoc, Auchentoshan, Aultmore, Cardhu, Glengoyne, Glen Grant, Mannochmore, Speyside, Tamdhu, Tobermory;

Cluster E (Light, Medium-Sweet, Low Peat, with Floral, Malty Notes and Fruity, Spicy, Honey Hints ): Bladnoch, Bunnahabhain, Glenallachie, Glenkinchie, Glenlossie, Glen Moray, Inchgower, Inchmurrin, Tomintoul;

Cluster F (Medium-Bodied, Medium-Sweet, Low Peat, Malty Notes and Sherry, Honey, Spicy Hints ): Ardmore, Auchroisk, Bushmills, Deanston, Glen Deveron, Glen Keith, Glenrothes, Old Fettercairn, Tomatin, Tormore, Tullibardine;

Cluster G (Medium-Bodied, Sweet, Low Peat and Floral Notes ): Arran, Dufftown, Glenfiddich, Glen Spey, Miltonduff, Speyburn;

Cluster H (Medium-Bodied, Medium-Sweet, with Smoky, Fruity, Spicy Notes and Floral, Nutty Hints ): Balblair, Craigellachie, Glen Garioch, Glenmorangie, Oban, Old Pulteney, Strathmill, Tamnavulin, Teaninch;

Cluster I (Medium-Light, Dry, with Smoky, Spicy, Honey Notes and Nutty, Floral Hints): Bowmore, Bruichladdich, Glen Scotia, Highland Park, Isle of Jura, Springbank;

Cluster J (Full-Bodied, Dry, Pungent, Peaty and Medicinal, with Spicy, Feinty Notes): Ardbeg, Caol Ila, Clynelish, Lagavulin, Laphroaig, Talisker.

This classification may be freely reproduced provided that the source is acknowledged as follows: Whisky Classified: Choosing Single Malts by Flavour, David Wishart, Pavilion Books, London 2002.

Interpretation

The order of the 10 clusters A-J maximizes the row-wise rank correlation of the underlying proximity matrix (details).  Readers who are familiar with malt whiskies may recognise the two extremes of strongly sherried malts (cluster A) and the heavily peated, mainly Islay malts (cluster J).  Adjacent to these polar benchmarks are the lightly sherried (clusters B and C) and lightly peated (clusters H and I) malts, with the light-bodied, floral and malty clusters, including four largely unpeated groups (clusters D-G) falling in the middle.

A ClustanGraphics tree that summarises the final classification of the 10 whisky types is shown below, in which the last 5 clusters are shaded differentially. This was obtained using Ward's method with the 10-cluster FocalPoint model.  The cluster of pungent, peaty Islay malts (J) is most distinctive, being maintained as a separate group to the end of the analysis, with the "sherries" of clusters A-C the next most distinctive, followed by clusters H-I.

The tasting profiles corresponding to each of the 10 clusters are available from clustan for those interested in taking this analysis further, or in using it as a case study.

The classification has been analysed by distillery location for Whisky Magazine - details here.

Applications

The classification may now be of use to retailers and consumers.   For example, if you like a particular malt then those in the same cluster should be of interest to your palate.  It could be of use by distillers, to type new distillations or to design new malts for marketing purposes.  There may also be scope for blenders to select malts from particular clusters to compile a sensory blend they are aiming to formulate.

The cluster analysis also finds an exemplar for each cluster, or that single malt which is typical of its class.  It can be useful in marketing, for stratified statistical sampling or for selecting a representative sampling panel.   For example, when organizing a whisky tasting it is helpful to choose at least one malt from each cluster to illustrate the full range. Indeed, this is done for the whisky tastings that accompany the presentation of Whisky Classified.

The development of a standardized tasting vocabulary framework may also be of value to the industry.  This study is possibly of limited value because the data were collected from open-ended descriptions by authors who were clearly not all singing from the same hymn book.  But in compiling a vocabulary of nearly 500 aromatic and taste descriptors, grouping them into 12 broad categories, and analyzing the resulting classification in these terms, we have developed a standard, consensual vocabulary which may now be used to type whisky products more objectively.  However, this framework clearly needs further development.

ClustanGraphics can be used identify new whisky products by reference to the classification.  A product's characteristics are entered into the program according to whether each of the 12 sensory feature groups are absent, hinted at, or pronounced.  ClustanGraphics4 then finds the best cluster to describe the product, and the malt which is closest to it in terms of the data entered.  Goodness-of-fit statistics indicate how close the product is to each malt or cluster.  However, a close fit may not be desirable if the objective is to discover a market segment which is unoccupied or under exploited.  In this way, the methodology may be of assistance in the design of new products.

It is also of interest to compare the authors in terms of how they rated the 86 malts.  We can classify them into types of tasters, and possibly work towards a scheme for recruiting a balanced panel of tasters.  Parallel work could be undertaken to develop a consumer segmentation, or a typology of whisky drinkers.  It was evident from whisky tastings that there are at least two distinct types of tastes at two extremes - the "Islays" and the "Sherries".

Understanding whisky consumers, and what they look for in their favourite brands, is a marketing pre-requisite for developing whisky products with enhanced consumer appeal.  John McGrath, Diageo Group Chief Executive, puts it simply: "You have to know a brand to grow a brand".

Validation

Our provisional classification was sent to the 86 distillers covered in the study, and to about 100 others including the authors of the 10 books reviewed, malt whisky societies, independent bottlers, blenders, retailers and academic researchers. Over 40% replied indicating strong interest within the industry, and of those responding over 95% thought the classification was reasonable overall, that the standard flavour profile was a reasonable description of flavours, and that the classification would be a useful guide to consumers.

The handful of negative responses we received all came from producers; significantly, we received 100% support for Whisky Classified 2000 from retailer and consumers organisations.  A number of whiskies were identified as being in the wrong clusters, six being noted by two or more respondents. The data were re-examined in the light of these comments, and the final classification was further adjusted to take account of most of these apparent misclassifications.

Several respondents felt that certain malts should not be clustered together because their peat content, distillery character or cask-maturation method differed.  One respondent felt that better results might be obtained using a trained tasting panel.  However, this was not the point of our study.  The malts were classified by how they are perceived by consumers, as represented by our "panel" of 10 expert authors, and not by the production or maturation methods used by the distillers.

Conferences and Seminars

Whisky Classified has been presented at several scientific conferences and seminars, which included in each case a tutored tasting sponsored by several distilleries.  Further details here.

Classification of Single Malt Whiskies ©Copyright 2000 by David Wishart, Edinburgh.