By Barry Keily
It turns out that the hallmark of a particular bourbon is neither its taste, its price, nor its clever design on its label.
Scientists have now shown that what really distinguishes a drop of Bulleit from a drop of Knob Creek or a drop of Jimmy B from a sip of Wild T are the traces it leaves on the coaster.
The discovery, described in detail in the diary ACS Nanois actually more significant and complex than it initially sounds. In practice, it can be used as a method to detect adulterated products. Most of the time, however, it’s just very cool.
Researchers led by mechanical engineer Adam Carruthers from the University of Louisville in Kentucky, USA, turned to the previously neglected whiskey stain chemistry, which was inspired by years of research into another popular drink: coffee.
Everyone who drinks coffee is aware that a small amount that falls on a non-porous or semi-porous surface and takes care of itself dries and forms a characteristic pattern.
This is known as “coffee ring” and occurs because the liquid at the edge of the spill evaporates faster than the material in the middle. This induces a capillary flow from the center to the outside, which becomes faster as the total amount of coffee decreases. The result is a striking ring that is darker on its outer edges.
The chemistry and physics of the process were first described in 1997, and coffee ring science has developed into a discipline of its own that produces dozens of papers every year.
Spilled bourbon is not like this. However, Carruthers and colleagues found that it did something just as interesting. It forms a network.
The researchers first noticed this when they observed diluted drops of bourbon that had to dry on glass surfaces. With remarkable attention to detail – perhaps a way of thinking that can only be achieved if you think about an empty whiskey mug – they found that the lane formations that evolved as the liquid evaporated appeared to be different depending on the brand.
Fascinated, they decided to take a closer look and examine the process under uniform samples under laboratory conditions. Using time-lapse microscopy, they were able to work on a number of bourbons.
In each droplet, they discovered non-volatile organic compounds, so-called aromatics, phenols and esters, that clumped together on the surface and formed a layer just one molecule thick. As evaporation progressed and the droplets became smaller, the layer collapsed and formed the pillars of a web.
They realized that these patterns were brand specific. To test this, they caused a number of spots to be made under which they were blind to the source bourbon. They then identified each drink only on the basis of the web layout – and guessed correctly in 90% of the cases.
They suggest that once it is properly coded this could offer a novel way to identify counterfeit alcohol.
But it would apparently only work in bourbon. By doing ACS Nano Carruthers and his team report that neither Scotch nor Canadian whiskeys develop the same type of webbing.
And it is precisely this type of detail – this commitment to research – that is the hallmark of true scientists.