Adding water to your distilled spirit will change its flavour. The question is: By how much? Researchers Chelsea Ickes and Keith Cadwallader report.

For whisky and other spirit drinkers, the big debate is always centred on should you drink whisky neat – no water or ice – or diluted with water?

The argument is not on lowering the inebriation effect of the alcohol with water, but on changing the flavour. The addition of water and its lowering of the spirit’s ABV percentage, opens up different and subtle flavours. 

A quick experiment you can do is to go to a supermarket, buy a carton of fresh, 100 percent pure grape juice and take a sip. Not saying which flavour is better, but there is no wine on the planet which tastes fruiter than non-alcoholic grape juice.

Or, try a glass of whisky, rum, or gin with a couple of ice cubes. As the cubes melt and lower the ABV of the drink, the flavour will subtly change. 

If you want to take this even further, try a non-alcoholic beer with a similar style beer with alcohol. There is a definite taste difference.

Why is this?

We perceive aromas through our nose and, according to Bernard Lahousse writing for FoodPairing blog, every aroma molecule behaves differently in solvents, depending on their physical properties. 

“As the term suggests, hydrophobic aroma molecules are water-adverse. They tend to flee when surrounded by water molecules, exiting into the headspace where they are easier to detect with our sense of smell,” says Lahousse. “Conversely, hydrophilic aroma molecules have an affinity for water molecules and prefer to remain in liquids.”

Alcohol (ethanol) has partially hydrophobic properties. This explains why the hydrophobic aroma molecules found in alcoholic beverages still remain in your wine and spirits despite the presence of alcohol, he says.

“On the other hand, the higher the volume of water, the more hydrophobic aromas you’ll have escaping from the liquid and moving into the headspace.”

The question is, how much does water change the flavour spirits and is this something that can be measured during the distilling process?

In the research paper “Effect of ethanol on flavour perception of rum”, by Chelsea Ickes and Keith Cadwallader of the University of Illinois and published by Food Science & Nutrition, the two scientists set out to answer this question.

They state: “In terms of both its physiological effects as well as its impact on flavour perception, ethanol is the defining component of alcoholic beverages. While ethanol’s effect on alcoholic beverage systems has been studied across a variety of disciplines, a comprehensive review of the literature is lacking. 

“The aim of this paper is to review the current literature on ethanol’s effect on flavour perception, exploring ethanol’s effects on the areas of physiochemical properties, instrumental measurements of flavour release, and sensory evaluation across a variety of alcoholic beverages including beer, wine, and distilled beverages and how changes in ethanol concentration can affect flavour perception.” 

According to the authors, this was the first sensory study to evaluate the effects of ethanol concentration on flavor perception of distilled spirits. Dilution series of two rums (R1 and R2) were evaluated to gain insight into the effects of ethanol concentration on the flavor perception of distilled spirits. 

Rums were diluted 1:2 (v/v) either with pure water to a final alcohol by volume (ABV) of 20% (R1-W and R2-W) or with an aqueous 40% ABV solution (R1-E and R2-E). 

The later dilution accounted for the flavor dilution effect while keeping the ethanol concentration the same as the original liquors. Descriptive sensory analysis was conducted on both dilution series and the original rums. 

Twenty-three attributes were evaluated consisting of eight aroma, four aroma-by-mouth, four mouthfeel, two taste, and five aftertaste terms. Results revealed 18 significant attributes for the R1 series. With the exception of silky mouthfeel, all attributes were rated highest in R1 and lowest in R1-E. 

The R2 series contained sixteen significant attributes, all of which were rated higher in R2 compared with R2-E. The flavor profiles of the original rums and those diluted with water were very similar, with the diluted rums generally having slightly lower attribute intensities. 

In contrast, the rums diluted with 40% ABV had significantly different flavor profiles than the original rums. Results indicate that diluting spirits with water may reduce the odor suppression effects of ethanol or enhance flavor release which appears to counteract the flavor dilution effect. 

The results found that physicochemical properties, such as the molecular level structure of water/ethanol matrices, are significantly altered as a function of ethanol concentration. Of particular importance to flavour perception is the effect of ethanol on the release of aroma compounds into the headspace of the beverage. Both static and dynamic headspace systems have been studied. 

In general, increasing the concentration of ethanol decreases the volatile headspace in static systems, while it tends to increase the volatile headspace in dynamic systems. Most importantly, sensory studies have demonstrated that ethanol concentration significantly changes the flavour profile of beverages to the point where sensory panellists are able to identify and articulate these differences. 

The current literature demonstrates that ethanol can have a huge impact of flavour release and sensory perception of alcoholic beverages. Additionally monitoring ethanol’s effects in systems as close to real life as possible (i.e., dynamic vs static evaluation) is important. Even with the extensive knowledge in the area, there are still many gaps in our understanding of ethanol’s effects on the flavour of alcoholic beverages. 

Ethanol has been shown to have a tremendous influence on flavour release and subsequent chemosensory perception in alcoholic beverages. Changes in ethanol concentration can affect consumers’ perception of alcoholic beverages in terms of aroma, taste, and mouthfeel.

“Our results showed that the original rums and dilutions with water were more similar to one another than expected. The samples were only statistically different for several attributes in each series. 

“These results support the age-old industry tradition of diluting distilled spirits to 20% or 23% ABV for blending and evaluation purposes, and in essence demonstrating that while the intensity of the attributes decreased slightly in the dilutions, the overall flavor profiles were very similar. The results for the ethanol dilutions were not expected, and further research is needed to better understand how ethanol interacts with sensory perceptions at high ethanol concentrations.”