Chemistry: Put some water in your whisky

An explanation for why diluting whisky with water can enhance its taste is provided in a study in Scientific Reports this week.

The taste of whisky is primarily associated with amphipathic molecules (molecules with hydrophobic and hydrophilic regions), such as guaiacol. Before bottling, whisky is diluted to around 40% alcohol by volume by the addition of water, which changes the taste significantly. Whisky enthusiasts will also often add a few drops of water to the spirit before drinking in order to further enhance the taste, but how and why dilution enhances this has not been clear.

Bjorn Karlsson and Ran Friedman carried out computer simulations of water/ethanol mixtures in the presence of guaiacol to study its interactions. The authors found that guaiacol was preferentially associated with ethanol and, at concentrations of ethanol up to 45%, was more likely to be present at the liquid-air interface rather than in the bulk of the liquid. In a glass of whisky, the authors suggest that guaiacol will therefore be found near the surface of the liquid, where it contributes to both the smell and taste of the spirit. At concentrations of alcohol above 59%, the authors found that ethanol interacts more strongly with guaiacol, which means the molecule is driven into the solution away from the surface. The findings suggest that the taste of guaiacol, and similar compounds in whisky, are enhanced when the spirit is diluted prior to bottling and this taste may be more pronounced on further dilution in the glass.