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Here’s the scientific reason it’s better to dilute whiskey with a little water

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It’s chemistry

Dilution of cask whisky (69 vol-% of ethanol) drives taste-contributing compounds such as guaiacol to its surface thus improving the taste.
Image: Björn CG Karlsson

Serious whiskey drinkers insist that it tastes better diluted with a little water — and, with the help of computer simulations, scientists now know why.

The distinctive taste of whiskey is largely caused by a molecule called guaiacol, which has one section that likes water and one section that doesn’t like water. In a study published today in the journal Scientific Reports, researchers simulated what happens to guaiacol when there are different concentrations of water, and which combination makes the molecule most potent.

Of course, the liquid in the Jack Daniels bottle isn’t pure alcohol to begin with. By the time whiskey is in the bottle, it’s usually already about 40 percent alcohol, though this can vary. And cask whiskey is even stronger, sometimes 65 percent alcohol.

The simulations showed that when there’s more than 59 percent alcohol in the drink, the molecule gets driven away from the surface. It floats around in other parts of the glass, which makes the taste worse.

But when there’s more water and less alcohol — say, up to around 45 percent alcohol — guaiacol is likely to be floating around at the top of the glass, which enhances both the smell and taste. So adding just a little bit of water can usually improve the taste of the drink because it ensures the molecule is at the surface instead of having it dispersed weakly in the rest of the mixture — proving that people are right when they say don’t drink your whiskey neat.

Correction: Astute whiskey drinkers have pointed out that whiskey on the rocks tastes different than whiskey diluted by water. We regret the ice.