American whiskey found to leave distinctive 'fingerprint' when it evaporates

American whiskey found to leave distinctive “fingerprint” when it evaporates
Credit: S. Williams/University of Louisville, via Physics

A team of researchers at the University of Louisville has found that unlike other whiskeys, American whiskey leaves a distinctive "fingerprint" behind when it evaporates on a flat surface. In their paper published in the journal Physical Review Fluids, the researchers describe how they came to find the unique patterns and note possible uses for such information.

The researchers report that one of their team members, Stuart Williams, became intrigued with the traces left behind on the bottoms of glasses that contained whiskey—so much so that he began taking pictures of them. Williams found they resembled images taken of the back of the human eyeball. He recalled an earlier study of residue carried out by a team studying Scotch whiskey—they had found that their whiskey formed concentric circles when it was allowed to evaporate. Intrigued by the differences in the two residues, Williams and fellow team members carried out a study of the residue left behind by American whiskeys.

In testing 66 brands, the researchers found that all but one left behind what they describe as "fingerprint" images. The name denotes that each brand had a distinctive image, not that they looked like human fingerprints. The team also found that such patterns only occurred under certain conditions—at and diluted to 40 - 50 percent proof. They suggest the differences found with different proofs indicate that alcohol level plays a role in fingerprint formation. But the main factor they note, is the unique way that American whiskey is made. Charred oak barrels are used during the maturation process, giving the whiskey its familiar smoky taste. whiskey from other countries, such as Scotland, are made using non-charred recycled barrels. The researchers suggest that solids from the charred wood make their way into the , which are in turn left behind when the liquid evaporates.

The researchers also suggest that their findings might be useful in a commercial sense—the fingerprints they leave behind might be used to identify counterfeits, or perhaps even as a way to test the quality of batches before they are shipped.

More information: Stuart J. Williams et al. Whiskey webs: Microscale "fingerprints" of bourbon whiskey, Physical Review Fluids (2019). DOI: 10.1103/PhysRevFluids.4.100511

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