You May Not Have To Drink Whiskey To Tell How Good It Is Anymore.

Those who know me would tell you that I have partaken in a bit of drinking in my day.  I am Scottish by heritage, yet American born. Therein lies the problem, the great “whiskey” and “whisky” debate has raged in my household for years. A recent article has been published about defining characteristics of American whiskey in comparison to Scotch whisky. American whiskey has been found to leave a brand-specific web-like design behind after it evaporates. Scotch whisky does not. 

Photo credit: https://pubs.acs.org/doi/10.1021/acsnano.9b08984#
Examples of the web-like designs produced by different whiskeys during the testing process.

The study of fluid dynamics has been an interesting field for a long time. Prior research on Scotch whisky has been performed and these studies found familiar “coffee ring” patterns when the Scotch evaporated.  This phenomenon occurs in many other liquids as well. The coffee ring effect is when different rates of evaporation along the surface induce capillary flow, drawing liquid to the outer edge of the stain, leaving a ring-like outline. Think of a dried drop of coffee on a piece of paper. The outer edges of the stian are defined after the solubles are drawn to the edge and left behind.

Traditionally, Scotch whisky is aged in barrels that are often recycled. American bourbon, or whiskey, is aged in new charred barrels. This distinction may give clues to why the researchers found what they have.

While testing the samples researchers found the American whiskey had higher amounts of solids and water-insoluble content. This difference in the chemical makeup tells researchers the content of the specific liquid has a significant impact on the monolayer composition and behavior. 

Researchers placed 1.0 microliter droplets on sterile glass slides and waited until the whiskey evaporated. Initially, the researchers found that American made whiskeys left nothing unusual behind after it had evaporated. They then diluted the whiskey with water to make a 20 – 25% alcohol by volume. This is when they found nanoscale agglomerates formed at the liquid-air interface. When diluted the micelles in the liquid move to the top of the sample, forming a monolayer that is eventually left behind. As the droplet shrinks during the evaporation process the thin film on the surface creases and folds making the unique web-like design. 

Photo credit: https://pubs.acs.org/doi/10.1021/acsnano.9b08984#
Image of the different phases of flow and monolayer formation found during the research.

The scientist tested dozens of brands of whiskey using this technique. They were successful in identifying brands 90% of the time. The research also states that out of the 66 samples tested, 65 whiskeys produced the web design. The one which did not was only aged for 42 years, much older than the average whiskey tested. The increased age of the sample increases the surface-active compounds which interrupt the monolayer and prevented the webs from forming. Conversely, unaged samples of the same dilution did not produce the webs either. The research determined the aging process directly contributes to the web design found. 

The researchers suspect this could be used in sample analysis and to identify counterfeit liquors. They will be hopefully pursuing this research with other liquids in order to find other applications, such as identifying characteristics of volatile liquids.  

This type of research engages people. In science, it is important to have people care about what you are doing in order to maintain support.  In this case, I think it is fair to say, “Mission accomplished.” 

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