Adding a drop of water to scotch has been part of pub lore and whisky chatter for decades. Bjorn Karlsson and Ran Friedman from Linnaeus University in Sweden explain why the splash of water seems to work using science to mitigate this long-standing debate.
What Karlsson and Friedman found is that when liquor is at or above 40 percent alcohol by volume, guaiacol molecules, found in higher concentrations in Scotch whiskies than in American, or Irish, tend to stay in the body of the liquid, away from the surface.
When Scotch is distilled, ethanol concentrations are as high as 59 percent, with aromatic guaiacol compounds attached. When diluted to roughly 40 percent, before bottled, ethanol accumulates near the surface accompanied by guaiacol. When ethanol levels are diluted to 27 percent— to when a Scotch drinker adds a splash of water—ethanol and guaiacol aerosolize, enabling the fragrant peaty and smoky and other aromatic compounds to be drawn in by the nose.
Knowing that taste and smell are linked, it is important to note that the right amount water is needed to enhance the flavors. As water dilutes the whisky, ethanol spreads allowing more of the guaiacol to surface. However, there is a fine balance, as the author’s note, “between diluting the whisky to taste and diluting the whisky to waste.” Too much dilution, and you lose that aerosolizing affect.
In short, every whiskey is chock full of its own variety of aromatics and compounds that are unique to each distillery location and the process in which it was bottled. Although water is added to reduce the strength of the whisky to regulated alcohol levels by volume, the splash of water can open new and subtle flavours that may not have been previously experienced. This is especially true with cask strength whiskies with its higher alcohol levels.
If you are curious, test a dram before adding a splash and then after to see if you notice a difference. Regardless of what science may tell us, the key is about preference and story as this is what embodies the lore.