Food & Drink What Happens When You Add Water to Whiskey

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There’s no doubt that adding water to your whiskey changes the flavor, but there’s a lot of confusion among whiskey drinkers about what exactly is happening in the glass—and whether or not that change in flavor is a good thing. To dispel all of this controversy, we spoke with our favorite scientist Matthew Hartings, a faculty member in the department of chemistry at American University (who previously helped unravel the chemical process within a G&T). Before we get to even one drop of water, we have to start with how whiskey is made. Whether a producer sources the base alcohol from a huge facility in Indiana or distills their own juice, whether they age their whiskey in wooden casks or only rest it briefly in glass containers, whether they add any other flavors or additives, every whiskey brand works to establish a balance between flavor molecules, water and ethanol. “The water and ethanol hold everything together like balancing on a tightrope,” Hartings says. “[Distillers] find a way to get all of these other flavor molecules to be steady, stable and not separate—like you would see when you mix oil and water—because that’s naturally what they want to do.” With a little time between the still and the customer, either in some sort of storage at the distillery or in the bottle, the whiskey eventually attains a stable balance.

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And then water comes in like a bomb and destroys that tranquil balance. “When you take a drop of water and put it in a glass of whiskey, you can see all these ripples and all these convection currents. That’s the water you’re adding disrupting that balance,” Hartings says.

Water causes new flavors to emerge from the glass, commonly referred to as “opening up” the whiskey. Hartings explains that the water isn’t adding any new flavors—it’s just water, after all. Nor does it alter the flavor molecules themselves. Instead, water radically rearranges the molecules inside. Hartings explains, “It’s kind of like playing pool. You start off with the racked balls. When they’re sitting in that rack, they’re happy being there. And even when you pull the rack away, they’re going to sit there. But you throw in that cue ball and it disrupts everything. Everything kind of moves around and has to find a new place to be.”

Adding water to whiskey also affects the aroma molecules. “The water and ethanol are like a kid hanging onto a helium balloon [representing molecules that trigger smells]. The kid sees something shiny [water, in this case], and all of a sudden they let their balloon go,” Hartings says. That balloon floats up into your nose and causes you to smell caramel or birch or dried fruit.

Water doesn’t affect all flavors equally, though. Some flavor molecules interact more strongly with water molecules than others. Picture again that kid holding a balloon, now picture him joined by an entire field of kids holding balloons of different colors—some blue, some green, some purple, all representing different flavors and smells. “You put on The Wild Kratts,” Hartings says. “The kids holding purple balloons really love The Wild Kratts. All of a sudden they let go of their balloons, and now you’re smelling more of that purple flavor than others. It’s really about how well those individual flavors interact with water.” The molecules that are attracted to water are less likely to leave the mixture when you add more water, whereas the molecules that are repelled by water are more likely to leave the glass and come to your nose.

While there is some experimentation into the effects of “hard” and “soft” water on beverages like coffee, the area is still fairly new for whiskey research. All Hartings can be sure of is that water quality does, in fact, impact taste by contributing different amounts of magnesium, calcium and carbonate, which help extract flavors in various ways.