There’s nothing quite like the pleasure of sipping a fine Scotch whisky, for those whose tastes run to such indulgences. But how can you be sure that you’re paying for the real deal and not some cheap counterfeit? Good news: physicists at the University of St. Andrews in Scotland have figured out how to test the authenticity of bottles of fine Scotch whisky using laser light, without ever having to open the bottles. They described their work in a recent paper published in the journal Analytical Methods.
As we reported last year, there is an exploding demand for expensive rare whiskies—yes, even in the middle of a global pandemic—so naturally there has been a corresponding increase in the number of counterfeit bottles infiltrating the market. A 2018 study subjected 55 randomly selected bottles from auctions, private collectors, and retailers to radiocarbon dating and found that 21 of them were either outright fakes or not distilled in the year claimed on the label.
Ten of those fakes were supposed to be single-malt scotches from 1900 or earlier, prompting Rare Whisky 101 cofounder David Robertson to publicly declare, “It is our genuine belief that every purported pre-1900 bottle should be assumed fake until proven genuine, certainly if the bottle claims to be a single malt Scotch whisky.” There’s also an influx of counterfeit cheaper whiskies seeping into the markets, which could pose an even greater challenge, albeit less of a headline-grabbing one.
That’s what prompted Alasdair Clark of the University of Glasgow to develop an artificial “tongue” capable of distinguishing between different brands of whisky. Announced last year, his device consists of two nanometal “taste buds”—one gold, the other aluminum—placed side by side and arranged in a checkerboard pattern. Each is chemically modified and then monitored to see how the nanometals’ interactions with light change in response to contact with a liquid. Having two taste buds on the artificial tongue gave them two distinct optical profiles of three different whiskies used in the experiments (Glenfiddich, Glen Marnoch, and Laphroaig), while still making just one measurement.
However, Clark’s artificial tongue isn’t looking for a specific kind of chemical; that’s what makes it a tongue as opposed to a sensor. Human tongues can distinguish between black coffee and apple juice, for instance, not because we sense particular chemicals in each but because over time we have learned to associate a certain flavor profile with each. That’s essentially what Clark’s artificial tongue is doing. And you still have to open the bottles in order to test the whiskies. Whisky producers and distributors are very interested in methods that would work while the precious bottles remain unopened.
Whiskies are remarkably complex, chemically speaking, despite the fact that the primary ingredients are water and barley (and/or other cereals). Yet how a whisky (or whiskey) is produced creates a unique chemical signature, or fingerprint. That includes time spent aging in a wood cask, which gives the spirit its telltale golden color, not to mention its smoky bouquet. As Allison Gasparini points out at Forbes:
Whiskies are chemically complex liquids which contain thousands of compounds that make up the distinct colors, aromas and flavors. Having a detailed understanding of the chemical composition of the bottle in front of you can be the difference between being certain a rare Scotch is what the label promises—or sniffing out a counterfeit.
Scientists are looking to many different techniques for gaining a better understanding of all those chemical compounds. For instance, researchers at the University of Tennessee’s Institute of Agriculture have identified many of the key aroma-active compounds responsible for the Tennessee whiskey’s distinctive flavor profiles using a combination of two techniques: gas chromatography-mass-spectrometry and gas chromatography-olfactometry. (Fresh-make distillate for Tennessee whiskey undergoes an extra filtration step prior to barreling called the Lincoln County Process, aka “charcoal leaching.”) They just published their full results, characterizing the whole process, in the Journal of Agricultural Chemistry earlier this month.
A spectral signal
Food scientists and chemists are also interested in using spectroscopy to identify the chemical compounds inside a whisky bottle. This involves shining a laser light into a substance, which scatters the light and breaks it into a spectrum of wavelengths. The different colors represent different wavelengths of light, which correspond to specific chemical compounds, and hence provide a unique “fingerprint” of the substance. The Scotch Whisky Research Institute (SWSRI) in Edinburgh, Scotland, is experimenting with a portable spectrometer that is sufficiently user-friendly to enable workers to measure trace sugar levels (one key characteristic for verifying provenance) with minimal training, as well as distinguishing between whiskies based on other chemical characteristics.
The challenge in applying such techniques to whisky is that the glass bottles themselves produce a large spectral signal, making it difficult to discern the chemical fingerprint of interest (that of the spirit inside). So spectroscopy is usually performed after whiskies have been removed from the bottle.
That’s the problem Holly Fleming and her colleagues at St. Andrews have solved with this latest paper. They figured out how to shape the laser light into a ring instead of a focused beam, thereby suppressing the noisy signal from the glass. They used a cone-shaped lens to focus the ring of light onto the bottle, which in turn refocuses said light into the whisky inside. So an expensive bottle of rare Scotch whisky can be tested for authenticity without wasting a single precious drop. Bonus: the same technique can also be used to analyze bottles of gin and vodka. That should make producers and distributors of fine spirits very happy indeed.
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