A little water in your whiskey?

Scientists test old advice that water improves flavor

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Two physical chemists walk into a bar. They order whiskeys, and a jolly Scotsman one stool over insists they add a splash of water to optimize the flavor of the spirits. Inspired by the smooth, smoky flavor, they vow to investigate a question whiskey enthusiasts answered decades ago: Does adding water to whiskey really make it taste better?

That’s the almost true story behind a paper published last week in the journal Scientific Reports. Bjorn Karlsson and Ran Friedman of the Linnaeus University Center for Biomaterials Chemistry are not whiskey drinkers, but Friedman did visit Scotland, and he raised an eyebrow at the locals’ dedication to watering down even the fanciest Scotch.

Like a good scientist, he wanted to test the assumption, so he teamed up with Karlsson and used computer simulations to model the molecular composition of whiskey.

There are two competing theories for why adding water to whiskey might improve the flavor, Karlsson said. The first suggests that adding water traps compounds that are unpleasant.

Whiskey contains fatty acid esters that have two very different ends. The head is electrostatically attracted to water and the tail is not. Fatty acid esters in water can form compounds called micelles. In micelles, all the tails come together in the middle while the heads form a sphere on the outside, like a bouquet of lollipops with their sticks all tied together on the inside. Adding water to whiskey could, theoretically, cause more micelles to form, trapping compounds that don’t taste or smell good.

A competing theory suggests that adding water releases molecules that improve the flavor. Water and ethanol don’t make for a perfectly uniform mixture. Aromatic compounds could become trapped in ethanol clusters and never reach the surface.

Karlsson and Friedman did calculations and found that fatty acid esters exist in such low concentrations that the first theory is unlikely, so they decided to focus on the second. In reality, “whiskey is a complicated mixture of hundreds or even thousands of compounds,” Karlsson said. They focused on just three: water, ethanol, and an aromatic compound called guaiacol.

Guaiacol is what gives whiskey that smoky, spicy, peaty flavor. These and other flavor compounds are not attracted to water and are more likely to become trapped in ethanol clusters.

In the researchers’ simulations, they found that the concentration of ethanol had a large effect on guaiacol. At concentrations above 59 percent ethanol (the alcohol content to which whiskey is distilled) the guaiacol was mixed throughout. Whiskey is diluted before bottling to about 40 percent ethanol. In the simulation, at 40 percent, ethanol accumulated near the surface, bringing the guaiacol with it. At about 27 percent the ethanol began to aerosolize, presumably freeing the guaiacol even further.