An excessive amount of water can cause whiskies to have a similar taste.

While adding a little water is thought to “open up” the flavor of a whiskey, a Washington State University-led study suggests that there comes a point at which the water becomes too much: about 20%.

The researchers chemically analyzed how the volatile compounds in a group of 25 whiskeys responded to the addition of water, including bourbon, rice, Irish whiskey, and both single malts and blended Scotch. They also had a trained sensory panel evaluate six of those whiskeys, three scotch and three bourbons.

Both tests found that adding a little water can change the aroma of the whiskey, but after 20%, you may start to have the same aroma. Since smell and taste are often closely linked, this likely affects the flavor of the spirit as well.

Tom Collins, associate professor at WSU and senior author of the study, said magazine foods. “By the time you get to the 60/40 whiskey to the water, the whiskey isn’t being discerned by the panelists; they start to smell the same, and that’s not really what you’re looking for.”

Working with Elizabeth Tommasino at Oregon State University to run the sensory panel, the researchers found that when using 100% whiskey, panelists could tell all of the whiskeys apart with ease. At 80/20 whiskey to water, they could still distinguish the types of whiskey within each group, but after adding more water, that changed.

While in each style of whiskey the flavors became more similar, the larger variety of scotch, whether single or blended, remained distinct from American bourbons and rayons.

Chemical analysis revealed similar results showing changes in the volatile compounds that entered the “headspace,” or the area above the liquid, when water was added.

Whiskey is a mixture of compounds that run the scale from hydrophilic to hydrophobic, in other words, those compounds that are attracted to water and others that repel it. Adding water sends the whiskey’s hydrophobic compounds into this headspace and leaves the hydrophilic compounds behind, altering the scent of the liquid.

The researchers found that the chemical analysis matched the learners’ painting impressions. For example, many Scotch whiskeys started out with a “peat” smoky aroma, but when they were toned down, they moved towards the richer fruity aroma known as “bum”.

“This happens because of the way dilution affects what’s in the headspace,” Collins said. “Compounds associated with smoky odors dissipate, and are replaced by compounds associated with fruity scents.”

Similarly, American bourbon was mostly associated with vanilla and oak notes at first, but as more water was added, they took on more of the aromas of the corn and grain used to make it.

The findings could help whiskey makers better understand how their customers would experience the drink if they chose to add water or take it “on the rocks.”

It also gives some support to the practice of serving whiskey with a large ice cube.

“This study helps understand why large square ice cubes are so popular because you can enjoy whiskey before it has been diluted to the point that it is not the same as whiskey,” said Collins.

Collins and colleagues are currently investigating the compounds that give Scotch whiskey its smoky aroma. They plan to present this ongoing work as well as this study at the World Distilled Spirits Conference in Edinburgh, Scotland which will be held May 9-11.

In addition to Collins and Tomasino, co-authors on this study include Aubrey Dubois of Michigan State University as well as first author B. Leighton Ashmore and James Harbertson of Washington State University.