Should you add water to whisky?

The researchers Karlsson and Friedman simulated water-ethanol mixtures. Guaiacol, a smoky aroma compound, stays at the surface at levels up to about 45 percent alcohol by volume; above 59 percent by volume the compound disappears into the liquid.

Their article Dilution of whisky, the molecular perspective appeared on 17 August 2017 in Scientific Reports. In the simulations the effect strengthened as the mixture was diluted further, to about 27 percent by volume. At high alcohol levels, ethanol instead binds the guaiacol to itself and pulls it along into the liquid.

Because you perceive the aroma of what is released at the surface, this explains why a splash of water can bring out the smoky character.

Whisky comes off the still at about 70 percent by volume and is around 55 to 65 percent by volume after ageing. Before bottling, water is added, often down to about 40 percent by volume.

Those figures come from the same article in Scientific Reports. For Scotch there is also a legal minimum of 40 percent by volume, laid down in the Scotch Whisky Regulations 2009. A bottle at cask strength is therefore not diluted and is usually well above the threshold above which guaiacol turns away from the surface.

Start with a few drops and taste after each addition. The researchers themselves state that there is no general answer to how much water gives the best flavour.

You cannot undo adding water, so work upwards in small steps. Use room-temperature water with no taste of its own, for example still spring water. Ice does something different from water: it lowers the temperature, so fewer volatile compounds are released, and it only dilutes as it melts.

No. The study looked at a single aroma compound in a heavily simplified mixture. Whisky contains hundreds of substances, and not every substance responds to dilution the way guaiacol does.

Guaiacol is mainly characteristic of smoked and peated whisky. For a bottle in which that substance hardly occurs, the research says little about what dilution does. Moreover, it concerns a computer simulation at molecular level and not a blind tasting with participants.

No, but added water cannot be removed again. Pour in small steps and keep an undiluted glass alongside if you want to compare.

Anyone who drinks without water does nothing wrong, and neither does anyone who adds a good splash. In both cases your own perception determines the result. At higher percentages many drinkers choose to dilute because the alcohol otherwise presses hard on the nose.