Flavor chemistry can help Tennessee Whiskey distillers achieve desired flavors consistently, say scientists

The studies at the UT Department of Food Science are working on characterizing both the flavor chemistry of different types of whiskey and their production processes. The ultimate aim of the program is to help whiskey manufacturers produce a consistent product tailored to the exact flavor profile they want.

Lincoln County Process​

Tennessee Whiskey undergoes charcoal filtration – a step required in order for the product to be labeled as ‘Tennessee Whiskey’ - and the changes in flavor chemistry during this process are of particular interest to scientists. (In order to be labeled as ‘Tennessee Whiskey’, the spirit must also be produced in the state of Tennessee from at least 51% corn after having been aged in Tennessee for at least 2 years in unused charred oak barrels.)

The filtration step is called the Lincoln County Process (LCP), after the location of the original Jack Daniel’s distillery. It is also referred to as 'charcoal mellowing.'

LCP is performed by passing the fresh whiskey distillate through a bed of charcoal, usually derived from burnt sugar maple, prior to barrel-aging the product. Anecdotally, it is believed that the LCP imparts a “smoother” flavor to Tennessee whiskey.

The precise nature of the LCP differs from distiller to distiller. Details are generally considered a trade secret, and so the process has been historically shrouded in mystery. Regulations simply specify the process should be performed: not how it should be carried out.

“In other words, all a manufacturer needs to do is pass the distillate over charcoal (an undefined amount—possibly even just one piece),” ​note scientists from the University of Tennessee team. “Thus, depending on how it’s conducted, the LCP step may not impact the whisky flavor at all. On the other hand, even small adjustments to the LCP can modify the flavor profile of the whiskey positively or negatively, potentially causing any number of surprises.”​

Distillers usually adjust parameters empirically throughout the whiskey production process, then rely on professional tasters to sample products, blending subtly unique batches to achieve the target flavor.

“By gaining a fundamental understanding of the changes in flavor chemistry occurring during whiskey production, our team could advise distillers about exactly what changes are needed to make their process produce their desired flavor goals. We want to give distillers levers to pull, so they are not randomly or blindly attempting to get the precise flavor they want.”​

Whiskey odorants revealed

A study published earlier this year in the Journal of Agricultural and Food Chemistry​​ by University of Tennessee scientists has already started to find these ‘levers’.

John P. Munafo, Jr., assistant professor of flavor science and natural products, and graduate student, Trenton Kerley, used samples from Sugarlands Distilling Company (SDC), in Gatlinburg, Tennessee, producers of the Roaming Man Whiskey.

Olfactory evaluations – smell tests - revealed that the LCP treatment generally decreased malty, rancid, fatty and roasty aromas in the whiskey distillates. As for odorants (the molecules responsible for odor), 49 were identified in the distillate samples using gas chromatography-olfactometry (GC-O). Nine of these odorants had not previously been reported in the scientific whiskey literature.

One of the newly found whiskey odorants, called DMPF, was originally discovered in cocoa. It is described as having a ‘unique anise or citrus-like smell’.

Another of the newly discovered whiskey odorants, called MND, is described as having a ‘pleasant dried hay-like aroma’.

Both odorants have very low odor thresholds in the parts-per-trillion range, meaning that the smells can be detected at very low levels by people but are difficult to detect with scientific instrumentation.

Thirty-one whiskey odorants were measured via stable isotope dilution assay (SIDA), all showing a decrease in concentration as a result of LCP treatment, albeit to different degrees. While the LCP appears to be selective in removing certain odorants, the process didn’t increase or add any odorants to the distillate.

“This new knowledge can be used to optimize Tennessee whiskey production,” ​say the scientists. “For instance, the process can be optimized for the removal of undesirable aromas, while maintaining higher levels of desirable aromas, thus “tailoring” the flavor profile of the finished whiskey.”​

With the only previous investigation into how charcoal treatment affects whiskey published in 1908, the scientists believe their study can reveal fresh knowledge for optimizing Tennessee whiskey production. But they conclude that, even with the aid of science, ‘whiskey making will still remain an impressive art form’.