1. The Colour of Whisky
The first of our Reference series on sensory evaluation, or the organoleptic properties of whisky, focuses on Appearance and specifically Colour.
Before we nose or drink a whisky we evaluate it visually. Unfortunately as a species that has developed excellent colour vision and visual acuity, an unconscious assessment is made automatically upon viewing. For this reason ‘blind’ assessment (different from a ‘blind’ tasting where the reviewer samples whisky of unknown origin) can take place by using coloured glasses, blue or black are popular, anything that blocks the colour and intensity of colour of the whisky contained within being perceived by the taster.
Perceptive, cognitive and emotional factors all influence the way we perceive and evaluate food. By removing the colour aspect we remove predispositions and assumptions made based on the colour of the whisky, allowing aroma and flavour detection and description to occur in an un-biased way.
As we are focusing here on visual description however, a clear glass is preferable. Whisky spirit when distilled is completely colourless (or Zero on our scale) and whisky gains its colour as a result of the maturation process.
Where does the colour of whisky come from
New make spirit coming off the still is a perfectly clear liquid, so where does the colour of whisky come from? Whisky is matured in oak casks, the size and shape of the cask will govern the area with which whisky can interact with it. The condition of the cask, virgin, toasted, charred, remnants of previous occupants, how many times it has been used or re-used and finally the length of maturation will all play a part in determining colour.
This is not an exact science however, for example it is not just the length of maturation but also the location and climatic conditions during this maturation will govern how the cask ‘breathes’. As oak wood is porous, the whisky inside will move into and out of the wood itself as it expands and contracts with temperature fluctuations. Similarly surrounding air pressure and humidity may amplify or reduce this.
The whole process allows spirit into the wood to extract compounds that may also react with the spirit itself to generate further aroma, flavour and colour. In one way the resulting colour of the whisky is linked to the other qualities, for example an intensely coloured whisky would be expected to have a large cask influence in aroma and flavour. However, colour compounds are not the same as flavour and aroma compounds. Whisky may extract differing amounts of each from the cask, producing a very flavourful but pale whisky for example. For that reason, visual assessment of colour can be largely ignored, and attempts to be un-biased by it should be pursued for accurate sensory evaluation. This can either be done physically (as in the colour-proof glass above) or by making a conscious cognitive decision and attempt to ignore visual presentation.
Identifying and describing colour
A description of the colour and intensity is usually slightly subjective despite colour chemistry being a much more exact science. The colour produced is due to light being absorbed or reflected, which can be measured using a spectrophotometer and given an exact read-out in terms of absorbance values at specific wavelengths. The typical human eye responds to light at wavelengths of around 390 to 700 nanometers (nm), known as the visible spectrum. Colour is detected by specific pigments (Rhodopsins) in the eye that absorb light at a range of wavelengths, however the three specific pigments have peaks at 424, 532 and 563 nm corresponding to ‘blue’, ‘green’ and ‘red’ respectively. As a result, the human eye isn’t quite as exact as a spectrophotometer and so a near approximation is achieved. Like other aspects of whisky evaluation, reference is widely used in colour descriptors too, with gold, amber and copper featuring heavily as well as reference to other wines/spirits associated with a more specific or uniform colour e.g. Champagne gold.
The standard scale for describing whisky colours is based on a 20 point scale of colour intensity, that can be exactly defined by specific light absorbance measurements. A good example can be found at Whisky Magazine’s site, including descriptors for each point on the scale.
Similar have also been published by Charles Maclean in his book Whiskypedia, due to its small size I regularly use this exact scale to confirm my own assessment of appearance. Shop for Maclean’s Whiskypedia: A Gazetteer of Scotch Whisky (New Edition) (opens Amazon)
Industry uses a slightly expanded scale either the Series 52 Brown Scale or European Brewing Convention (EBC) scale. Series 52 is the original Lovibond® Brown colour scale now currently used for the colour grading of whisky, honey and similarly coloured liquids or syrups. The standard version of this scale includes a series of 23 amber/brown glasses although other values are also available.
The EBC colour scale, developed by the Institute of Brewing and the European Brewing Convention, is a recognised method for colour grading of beers, malts and caramel solutions as well as similarly coloured liquids. It has a range of 2 to 27 visual units; yellower pale worts and lagers at the low end of the scale and the amber of dark worts, beers and caramels at the upper end of the scale. If the sample falls outside this range (e.g. concentrates, syrups) then sample dilution and/or a different path length cell can be used to bring the reading within the EBC range. This scale measures absorbance of light at wavelength 430nm. A similar system is used in America termed the Standard Reference Method (SRM) Beer colour chart with 40 colour grades. The SRM value is 12.7 times the log of the attenuation experienced by light of wavelength 430 nanometers (deep blue) in passing through 1 cm of the beer (or wort).
Is the colour natural or not?
For purists the statement ‘No added Colour’ or ‘Natural Colour’ is a must on a whisky bottle as it means or suggests that the colour has not been adjusted by the addition of spirit caramel. Spirit Caramel additive also known as E150a is a food colouring made by heating of sugars without any other additive or preservatives. It has long been used in the whisky industry to provide a uniform colouring of a natural product that might vary in colour due to cask maturation.
This makes sense when you consider Blends or Bulk vatted or married expressions where hundreds of casks at a time may go into the mix to produce a uniformly flavoured product such as a classic blend like Johnnie Walker Red Label or single malt like Glenfiddich 12 Years Old. If every batch tastes exactly the same, it should also look exactly the same, in a process termed harmonization.
Consumers would be highly wary or ascribe a difference in taste to a very dark versus an almost colourless bottling of the same product. Spirit caramel adds little or no flavour to the whisky depending upon who you ask, indeed only tiny amounts are needed to colour a bottle or whole batch of whisky. I suspect the flavours in most whisky are already far stronger than any caramel influence anyway so I don’t dwell on this issue and have never knowingly identified ‘spirit caramel’ as an overriding flavour.
Cynically however E150a could be used to produce a rich deep colour in a whisky to suggest great age or maturation, and there is clearly no place for it in single cask bottlings or other highly individual bottling series. Personally I would prefer it not used at all. I find nothing more fascinating than a young Islay malt with barely a suggestion of gold or even gin clear liquid and then a massive punch of flavours and aroma’s, proving that there really isn’t any connection between the visual and chemosensory (flavour and aroma) elements of whisky. I do understand though that a consumer-product relationship is established to the point that even whisky in opaque bottles (i.e. where the consumer cannot even see the colour of the whisky at the point of selection or purchase) is coloured, mostly for the reason that once it is poured it will be automatically and instantly visually assessed.
Traditionally nothing may be added to single malt scotch whisky, a reasonably pure product, without threatening its status. With the exception of spirit caramel or in more recent legislation specifically E150a. Differing legislations apply around the world however, as do bottling requirements. For reference, bottles of whisky exported for sale in Germany or Denmark must have the use of colouring declared upon the label to meet legislation.
How we use colour
We rate our whiskies to the standard 20 -point scale described above, usually with visual reference to a colour chart for confirmation. In the absence of added colouring the following are usually indicative: (0-5) clear/pale gold young or refill cask matured, (6-11) medium to full gold 1st fill ex-Bourbon or refill Sherry casks, darker gold (12+) well aged, any copper or bronze hue may indicate Sherry and darker (14-20) usually 1st fill ex-Sherry, crimson or pink hue may indicate Port or Red Wine maturation or finishes. The use of American white oak, European “Sherry” Oak or French “Tannic” Oak are likely to only introduce a variance of around 1 point on the scale as the predominant colour is derived from the casks former occupants more than variance in colour of the oak wood, aside from charring/toasting or other physical procedures performed on the wood which may influence colour.