Why You Should Add Water to Your Whiskey

There's a lot of science behind the time-honored tip.

Scotch and water in a glass with ice and a lemon garnish
Photo: Viennetta / Shutterstock

Whiskey aficionados are known for having strong opinions about, well, most things. They quibble over the concept of terroir in whiskey, turn their nose at bottlings that are chill-filtered, and debate whether age is indicative of quality. The list of contentious whiskey-related subjects is seemingly endless, but one tasting-related topic that divides enthusiasts is whether or not to add water to a glass of whiskey to open it up, and if one decides to do so, where that water should be sourced from, as well as how pure it should be.

Before a whiskey is bottled and long before it glides into your glass, the spirit is introduced to water during various phases of its production process. From steeping barley to initiate germination (an integral part of the pre-fermentation stage for many whiskeys that use malted barley) and mashing, to fermentation and proofing, the value of using quality water in whiskey making cannot be understated. While most connoisseurs acknowledge the significance of a distillery's water source during the production process, the importance of the type and volume of water used to dilute a whiskey during a tasting is occasionally overlooked, and not always understood.

But with an increasing volume of research suggesting that added dilution gives drinkers a well-rounded perception of a whiskey's flavor profile and character, it's a good time to get down to the bottom of what's actually happening in the glass when water is added to whiskey.

The Science of Adding Water to Whiskey

"Whiskey comprises alcohol molecules, water molecules, and various flavor compounds, which arrange themselves in a particular composition," explains Calum Fraser, chief blender at Bowmore. "However, when water is added and the alcoholic strength changes, so does the make-up of the compounds and molecules relative to each other, which in turn alters the flavor profile."

It's an ever-changing relationship depending on the flavor compounds that exist within a certain whiskey. These are influenced by an array of factors, from how the spirit is filtered to cask finishes. "Due to molecule by molecule variation in solubility in water, this can cause certain flavors to be more 'visible' to the nose, particularly those that are drowned by the alcohol at higher strength," Fraser says. In essence, when a whiskey is diluted, certain flavor compounds go from being soluble to insoluble as the strength of the spirit changes. Soluble compounds are less apparent when tasting, while insoluble compounds reveal themselves to drinkers as flavors.

These shifts in flavor are typically a result of the way ethanol molecules (or the alcohol content in whiskey) recalibrate themselves among the other molecules and the water itself. Since there are two poles to ethanol molecules –– one being hydrophilic, and the other hydrophobic –– at very low concentrations, ethanol accumulates at the surface of a glass of whiskey. It's at the surface that these molecules align themselves in their preferred direction with the water-repelling (i.e hydrophobic) side facing upwards towards the air.Above a certain concentration, the ethanol at the surface reaches capacity, and some of the molecules that cannot fit retreat into the depths of the liquid, becoming soluble, and therefore less noticeable to the human palate.

Why Does the Kind of Water Added to Whiskey Matter?

As one can imagine, this level of chemistry-heavy whiskey chat tends to be a touch dull for the average drinker, so it's easiest to just think of the science in terms of how flavors are actively perceived, instead of how ethanol molecules are rearranging themselves.

As far as the type of water's effect on a whiskey's flavor is concerned, it's best to avoid anything too mineral-heavy. "From a human perception, it is essential to use water free from any contaminants prior to dilution so as not to impair the characters developed during the processes taking place at the distillery, maturation warehouse or the blending room," says Fraser. "In this regard, for blending room activities we assess the water used separately prior to use for any cask or production sample dilution where required."

While Fraser and Bowmore take a more analytical approach to water selection for tasting their whiskeys, other industry professionals such as Dawn Davies MW, head buyer at The Whisky Exchange, simply consider the pH level. "With regards to the purity of water, for me, I am happy using a fairly neutral water," she says. "For me, it is the pH more than a water's flavor that will affect the taste. If a water has a very distinct flavor then it will absolutely change the taste, but since you aren't typically adding huge amounts — I recommend using a pipette — it shouldn't really cause too many issues." (For imbibers who don't have a pipette stocked at home, you can use a straw to add small doses of water by dipping it in a water glass and holding the top to retain the liquid, then removing your finger to release the water.)

Does All Whiskey Benefit From Added Water?

The volume of water added to a whiskey during a tasting should always be minuscule, but the age of the whiskey can determine whether or not it'll benefit from dilution at all. "For established ongoing expressions such as Bowmore 12 years old, I work with samples at 20% ABV [the industry average for tasting with dilution], checking to make sure all the characteristics I expect are there – and just as importantly I don't expect aren't there," Fraser explains. "The addition of water for these lower aged expressions reduces the intensity of the alcohol, unmasking all the flavors for assessment."

Older whiskeys which have gone through a long maturation cycle require more delicate dilution, if any at all, as to not amplify unwanted wood-driven notes and to give the highly aged whiskey a chance to flaunt its time-filled nuances in flavor. "Highly aged expressions, such as the luxurious ARC-52—aged for 52 years—the long maturation time in fine oak casks has mellowed the effect of the alcohol and opened up the complex array of luxurious characteristics…Adding water to a whisky of that nature, in my opinion, would destroy the perfect balance of the flavors which time has presented."

How Much Water Should You Add to Whiskey?

In regards to the tasting process, Blair Bowman, an award-winning whisky consultant and broker, shares his take. "I always recommend trying a whisky neat (even at cask strength) then if I felt it needed it — and it depends on the whisky and whether I'm drinking for enjoyment or to assess a whisky — I would then gradually add water," says Bowman.

The main rule of thumb for whisky tasting is to add water until the alcohol burn goes away. This amount varies for each person depending on their tolerance of spirits; If they are more used to drinking wine or beer at lower alcoholic strength, then they may add more water until the spirit 'burn' diminishes and the whisky opens up."

By tasting the whiskey at various ABVs as you dilute it — and, in turn, transform its chemical structure — you are able to better understand the flavors and textures at play. As is the case with most tasting methods, there's always a bit of subjectivity. "[R]eally, it is about the individual whisky and the individual person that depends on whether you add water or not…there's no precise method, it is what you feel is right for the liquid," says Davies.

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