Just like wine, whisky is an amazingly complex beverage, with as many ways to drink it as there are drinkers.
Purists will tell you the only thing you should add is a few drops of water just before drinking to improve the flavour, and scientists have just figured out why – but we’ll get back to that.
On a chemical level, whisky contains several hundred aromatic and flavour compounds that work together to produce a complex flavour profile that connoisseurs are willing to pay top dollar for. Just this week, a bottle of Black Bowmore 1964, sold at auction for more than A$18,800, or an eye-watering A$800 per shot.
The many stages of the production process start with drying and grinding malted barley, then mixing it with yeast. This creates a product similar to beer, and it’s about 5-10% alcohol by volume (ABV).
In traditional processes this liquid is transferred to a copper still. The liquid is heated in the still so that the alcohols within it vaporise and rise up the neck, where they condense and can be isolated – otherwise known as distillation. Undesirable components from the start and end of the distillation process are removed, and only the middle portion moves on to the next step.
This liquid, known as the ‘heart’, winds up at about 60-70% ABV at this stage. This concentration is known as ‘cask strength’, and is carried on to the maturation process. The whisky is sealed in wood casks, and aged for at least 3 years. Once the ageing is complete, the final spirit is diluted down to about 40% ABV before bottling.
A large part of whisky’s characteristic flavour and complexity comes from the ageing process. Initially the whisky has a sharp, metallic taste which becomes significantly more mellow and smooth as it ages.
Different types of wood, the age of the cask, temperature, humidity, and other environmental factors all contribute to the final taste of the spirit. As it ages, some components of the whisky are drawn into the porous wood of the cask.
Similarly, the whisky draws compounds out of the wood. It is through this ‘give and take’ that important and desirable flavour and aroma compounds find their way into the whisky. Chemical compounds such as esters add sweeter and fruitier fragrances and flavours, such as notes of crisp apple or pear.
Aldehydes are responsible for spicy, floral or botanical flavours, and lactones add woody, nutty notes. However, the most characteristic of many whiskies are the smoky, peaty flavours that are contributed by a class of compounds known as the phenols.
So, if producers have gone to that much trouble to make the perfectly aged and chemically robust whisky, why would you add plain old water?
Swedish scientists have just figured out what’s happening to some of these phenols in whisky on a molecular level. Their focus was on one particular phenolic compound, guaiacol, which is responsible for a number of the characteristic smoky flavours associated with many Scottish whiskies.
Through extensive computational modelling, they investigated how guaiacol behaved at different alcohol concentrations.
Their study found that at higher concentrations (above 59%, or roughly ‘cask strength’), guaiacol is bound within the bulk of the beverage. However, at dilutions slightly below bottle strength (<45% ABV), that guaiacol is more likely to be located at the surface of the liquid, meaning that it is more likely to evaporate, and add to the aroma, or ‘nose’ of the whisky.
Diluting the whisky with water increases the amount of these compounds at the liquid/air interface. What is true for guaiacol may also be true for other flavour compounds present in the whisky. Higher concentrations near the surface of your glass means that these valuable flavour compounds hit your nose and tastebuds first, and your whisky starts tasting a whole lot better.
TL,DR: Diluting the whisky prior to bottling drives key flavour compounds to the surface of the liquid, and diluting it a further in the glass adds to this effect, changing both the bouquet and taste of the whisky. Ultimately, the best way to drink whisky is in the way you most enjoy it, but the science suggests that adding a splash of water before you imbibe will change the experience for the better. Cheers!
Nick is a PhD candidate in Forensic Science at Flinders University, where his research interests focus on trace evidence and gunshot residue.