Chemistry in Pictures: When whiskey runs dry

Stuart J. Williams of the University of Louisville and Orlin Velev of North Carolina State University teamed up to see whether they could tell whiskeys apart just by how they looked when dried, and it turned out they could. (The one up top is Rabbit Hole, and the one below is Wilderness Trail.) As these droplets of diluted whiskey evaporated, the ethanol in these 1 µL droplets evaporates faster than the water. In order to evaporate, though, ethanol needs to slide to the droplet’s outer surface, and it carries with it the whiskey’s water-insoluble compounds—including flavor compounds like aldehydes and esters. The result is a thin layer of these compounds forming on the top of the droplet. As the alcohol and water continue to evaporate, the droplet gets smaller, which causes the organic layer to collapse, twist, and fold on itself, leaving behind these patterns. The team found these patterns were most visible in American whiskeys; this might be related to the fact that whiskeys made in the US (with the exception of corn whiskey) need to be aged in new charred oak barrels, a unique-to-US requirement that leads to more water-insoluble content.

Credit: Stuart J. Williams. Read the paper about this research here: ACS Nano 2020, DOI: 10.1021/acsnano.9b08984

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