Chemistry of bourbon reveals unique fingerprint

Producing a great whiskey requires the perfect combination of grains, barrels, ageing and climate. Now, the emerging chemistry of ‘brown spirits’ is finding that whiskeys have distinct chemical signatures that match the complex combinations that create their distinctive flavour profiles.

The chemical fingerprinting of bourbon and other whiskeys was the topic of a presentation at the 246th National Meeting & Exposition of the American Chemical Society (ACS).

Dr Thomas Collins’ research team has profiled more than 60 American whiskeys, resulting in a treasure trove of information that could prove useful for whiskey makers large and small, as well as for regulators. For his doctoral degree, Collins conducted comparable work on wines, giving winemakers a new perspective on how oak barrels contribute to aroma. He says distilleries could likewise benefit from this research into whiskey.

“Whiskeys’ chemical profiles could be used for distillers’ quality assurance or process-improvement programs,” said Collins, research director at the University of California-Davis Food Safety and Measurement Facility.

“In addition to that, they could be used to help speed-up production. I think many of the small distilleries - the craft distilleries that are cropping up - may be interested in doing that. It’s difficult to get a whiskey business going when you typically need to age the product for three or four years or longer.

“Another application of our broader project that includes international whiskeys could be helping manage counterfeit and fraud, which is a huge issue for expensive scotches that are exported from Scotland to customers all over the world.”

Using chemistry’s latest analytical tools, Collins’ team found that a single whiskey sample can contain hundreds of non-volatile compounds, the ones that tend to stay in the liquid rather than evaporate off. Added up across multiple samples, the number of compounds comes to about 4000 - a scientific testament to the complex molecular mingling that occurs as a spirit ages, sometimes for decades, in a 53-gallon oak barrel.

Of the thousands of compounds in the resulting products, the scientists narrowed the field down to 50 to 100 contributors, including fatty acids, alcohols and tannins, comprising a spirit’s signature that distinguishes a Tennessee whiskey from a bourbon. But not all varieties of whiskey tested were easily identified through chemical profiling, Collins noted. Though the ratios of grains used to make them differ significantly, bourbons and rye whiskeys made in the same distillery developed chemical signatures that looked more like each other than those of bourbons and rye whiskeys, respectively, of another producer.

“In some cases, there’s a distillery fingerprint that overrides the difference in the grains,” Collins said.