The best way to drink whisky, according to weird science

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

That’s the almost true story behind a paper published this week in the journal Scientific Reports. Bjorn Karlsson and Ran Friedman of the Linnaeus University Centre for Biomaterials Chemistry are not whisky 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 whisky.

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

Whisky 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 whisky 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 flavour. Water and ethanol don’t make for a perfectly uniform mixture. Aromatic compounds could become trapped in ethanol clusters and never reach the surface. Our tongues are only capable of identifying the flavours, sweet, salty, sour, bitter, and umami (savoury), so aroma is really important for detecting all the other flavours that connoisseurs appreciate in whisky.

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, “whisky 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 whisky that smoky, spicy, peaty flavour.

In the researchers’ simulations, they found that the concentration of ethanol had a large effect on guaiacol. At concentrations above 59 per cent ethanol (the alcohol content to which whiskey is distilled) the guaiacol was mixed throughout. Whiskey is diluted before bottling to about 40 per cent ethanol. — Washington Post