For many people, adding anything to a single malt whisky is close to sacrilege, but it's generally acknowledged that adding a drop or two of water to lesser blends enhances the flavor. The question is, why? At Sweden's Linnaeus University, researchers Björn Karlsson and Ran Friedman have come up with an answer from a molecular perspective.

When whisky is distilled, it has a strength of 70 percent alcohol per volume, but this is watered down to 40 percent to improve the flavor as well as protecting the drinker's stomach lining. To further improve the taste, many whisky drinkers will add a little more water before taking a sip.

According to Karlsson and Friedman, why this works wasn't understood previously, but a better understanding of the chemistry of whisky has provided an answer. The taste of whisky comes from amphipathic molecules that have hydrophobic and hydrophilic parts. One key molecule is guaiacol, which is produced by the grain for malt whisky drying over peat smoke to produce the spirit's distinct, smoky flavor.

Using computer simulations, Karlsson and Friedman studied water/ethanol mixtures in the presence of guaiacol and found that guaiacol preferentially associated with ethanol molecules and that in concentrations of ethanol of up to 45 percent, the guaiacol is more likely to be present at the surface between the whisky and the air.

"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," says Friedman. "Interestingly, a continued dilution down to 27 percent resulted in an increase of guaiacol at the liquid-air interface. An increased percentage, over 59 percent, 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."

This seems to explain why adding a little water improves the flavor, but the scientists acknowledge that there is still a strong element of individual taste involved.

"How we experience taste and aroma is highly individual," says Karlsson, "Some people choose to add ice cubes to their whisky, to cool it down and give it a milder taste. Thus, there is no general answer to how much water you should add to your whisky to get the best taste experience."

The research was published in Scientific Reports.

Linnaeus University