Adding water to whisky is often thought to enhance its flavor, but a new study led by Washington State University has found that there is a limit to this practice. According to the study, adding more than 20% water to a whisky can cause it to lose its distinct aroma and potentially impact its flavor.

Through meticulous chemical analysis, the team examined the behavior of volatile compounds in 25 different whiskies, encompassing bourbons, ryes, Irish whiskeys, single malt and blended Scotches. A panel of expert tasters evaluated six selected whiskies, including three Scotches and three bourbons.

In both experiments, it was discovered that a small addition of water could alter the aroma of the whiskies. Still, once the dilution reached 20%, they exhibited a similar aroma. Considering the close association between smell and taste, this observation likely influenced the overall flavor profile of the spirits.

“If you want to enjoy a specific whisky, this suggests that you don’t want to dilute it by more than 20%,” says senior author Tom Collins. “By the time you get to 60/40 whisky to water, the whiskies are not differentiated by the panelists; they begin to smell the same, and that’s not really what you’re looking for.”

In collaboration with Elizabeth Tomasino from Oregon State University, the research team conducted a sensory panel to investigate the effects of water on whisky. The panelists demonstrated an impressive ability to distinguish between different whiskies when consumed neat at 100% concentration. Even at an 80/20 whisky-to-water ratio, they could still discern variations within each group. However, adding additional water diminished the ability to differentiate flavors.

While the introduction of water increased similarities in aroma profiles within each whisky style, the broader category of Scotches, including single malts and blends, maintained a distinctive character compared to American bourbons and ryes.

Complementing the sensory analysis, the chemical examination mirrored these findings by revealing alterations in volatile compounds in the headspace, the area above the liquid, upon water addition.

Water Unleashes Whisky’s Complex Chemistry: The Science Behind Aroma Transformation

Whisky, a fascinating blend of hydrophilic and hydrophobic compounds, undergoes a remarkable metamorphosis when water is introduced. This addition causes the hydrophobic compounds to rise into the headspace while the hydrophilic ones remain behind, resulting in a captivating change in the liquid’s aroma.

The study findings aligned perfectly with the perceptions of the knowledgeable panel. For example, many Scotch whiskies’ initial smoky and “peat” aroma underwent a captivating shift towards a luscious and fruity scent, affectionately referred to as “pome.” The chemical analysis provided solid evidence that validated the experienced tasters’ impressions.

“This happens because of how dilution affects what’s in the headspace,” explains Collins. “The compounds associated with smoky aromas dissipate, and they were replaced by compounds associated with fruity aromas.”

Similarly, the addition of water to American bourbons alters their scent profile. While initially associated with vanilla and oak scents, introducing water brings forth the aromas of corn and grains used in their production.

These findings provide valuable insights for whisky makers, enabling them to understand better how customers will experience their drink when water is added or served “on the rocks.” Furthermore, the research supports the popular practice of serving whisky with a single, large ice cube.

“This study helps to understand why those large, square ice cubes have become so popular because you can enjoy the whisky before it gets diluted to the point that it’s not the same whiskey,” adds Collins.

Collins and his colleagues are presently engaged in an in-depth analysis of the compounds responsible for the distinctive smoky aroma of Scotch whiskies. They intend to share the progress of their ongoing research, along with the findings of this study, at the upcoming Worldwide Distilled Spirits Conference scheduled to be held in Edinburgh, Scotland, from May 9-11.

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