“The taste of whisky is primarily linked to so-called amphipathic molecules, which are made up of hydrophobic and hydrophilic parts. One such molecule is guaiacol, a substance that develops when the grain is dried over peat smoke when making malt whisky, providing the smoky flavour to the whisky”, Karlsson explains.

Karlsson and Friedman carried out computer simulations of water/ethanol mixtures in the presence of guaiacol to study its interactions. They found that guaiacol was preferentially associated with ethanol molecules and that in mixtures with concentrations of ethanol up to 45% guaiacol was more likely to be present at the liquid-air interface than in the bulk of the liquid.

“This suggests that, in a glass of whisky, guaiacol will therefore be found near the surface of the liquid, where it contributes to both the smell and taste of the spirit. Interestingly, a continued dilution down to 27% resulted in an increase of guaiacol at the liquid-air interface. An increased percentage, over 59%, had the opposite effect, that is to say, the ethanol interacted more strongly with the guaiacol, driving the molecule into the solution away from the surface”, Friedman continues.

Source: Why whisky tastes better when diluted with water | Lnu.se