Here's the kind peer-reviewed scientific study and journal article that we can all get behind: how to make your whiskey taste better. This year, scholars Björn C. G. Karlsson & Ran Friedman took a look at the molecular makeup of whiksey, and specifically, how dilution with water affects the presence of flavorful compounds that make the sipping experience even more enjoyable.
Published in journal Scientific Reports, the research focused on three main components of whiskey, specifically Scotch, who spell it whiksy with no extra “e”: water, ethanol (alcohol), and guaiacol, an aromatic compound that helps give whisky it's smoky, peaty, pleasantly spicy grain flavor. According to the study, “Whisky is distilled to around 70% alcohol by volume (vol-%) then diluted to about 40 vol-%, and often drunk after further slight dilution to enhance its taste.” So the pair sought to find out how dilution by water, lowering the ethanol percentage and ABV, affected the aromatic guaiacol molecules.
Turns out, the ethanol and water don't always mix super well. The ethanol tends to push the guaiacol down to the bottom, trapping the molecules inside the glass, instead of letting them reach your nose. But by diluting the whisky, and changing the ABV, you bring the ethanol to the surface, allow the aromatic compounds to become air-born. So, the water concentration allows the ethanol to present itself further at the surface of the liquid, and then the guaiacol molecules interact with the air, and thereby your smell and taste sensors.
So, drink it on the rocks if you must (we don't), but in every case, you should at add a few drops of water to maximize your glass. Whisky is usually bottled around 40-45%, but according to the study, adding water to bring the ABV closer to 30% gives you the highest amount of aersolized guaiacol, and therefore the most flavor.
Of course, this is still all a computer simulation, but the researchers have backed up what the anecdotal evidence has said for centuries: whisky simply tastes better with a splash of water.
Read all about it at Nature.com: Dilution of whisky – the molecular perspective