Many whiskey aficionados like to add a splash of water or an ice cube to a glass of whiskey before drinking it to help “open up” the spirit’s flavor and aroma. That’s because most of the flavor in whiskey is in the form of ethanol-soluble molecules. The higher the proof of the whiskey, the more flavor molecules dissolved in the alcohol portion. Cutting the spirit causes some of those flavor molecules to come out of solution, so they are more readily smellable and tasteable. Dilution also reduces the burn and bite of the alcohol when sipped so that we can sense more of the flavor nuances.
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Taste Off: Tap Water Versus Distilled Water
We wondered if the flavor could be further amplified by using distilled water instead of tap water. We held a tasting of anonymized samples, diluting whiskey with liquid and ice forms of both tap water and distilled water.
There was a clear consensus that distilled water was better, though the preferred amount of dilution varied among tasters (from 1 teaspoon to 1 tablespoon of water added to a 2-ounce pour of 100-proof spirits). Tasters found that samples cut with distilled water and ice were both smoother sips and exhibited more robust aromas and notes of smoke, caramel, and butter.
Why Distilled Water Enhances Spirits' Flavors—and Tap Water Muddies Them
Why? Water is a powerful solvent, so tap (and spring) water is full of dissolved minerals from the earth, water pipes, and the container it is stored in. Adding that water to your whiskey also adds the taste of all the minerals, which can muddy the flavor of the drink.
Distilled water has had all its minerals removed, so not only is it neutral in flavor but it is chemically very eager to dissolve whatever it can. When it is added to whiskey, the ethanol dissolves readily into the water, which frees more of the flavor compounds, making the flavors in the whiskey much more vivid.