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There really is something unique about Tennessee whiskey, study finds

Fresh make distillate for Tennessee whiskey undergoes an extra filtration step prior to barreling called the Lincoln County Process, aka "charcoal leaching." (The moniker comes from the Tennessee county where Jack Daniels set up its first distillery.) If it doesn't go through that process, it can't legally be sold as Tennessee whiskey, although different distilleries have their own methodologies within that requirement.

Charcoal is a common substance used for filtration in distillation, and the charcoal chips used in the Lincoln County Process are made from selected sugar maple trees native to the region. Filtering the whiskey through charcoal is thought to improve its flavor by jump-starting the aging process, removing more congeners, even before the whiskey is poured into charred oak barrels for aging.

[...] First, Munafo and Kerley established a baseline flavor profile by analyzing the distillery's unfiltered whiskey with a combination of two techniques: gas chromatography-mass-spectrometry and gas chromatography-olfactometry. (The latter tool enabled them to sniff out the individual components as the compounds were separated.) Next, they used aroma extract dilution analysis to tease out which compounds were most critical to the whiskey's flavor profile, and in what concentrations.

The team then soaked several other batches of distillate in the charcoal for between one to five days and analyzed those resulting samples. "If you taste the control that hasn't been treated, and the one that has been treated, there is clearly a reduction of these harsh attributes," said Munafo. That difference in flavor corresponded to the significant changes they measured in the chemical composition of the unfiltered and filtered whiskeys. The levels of some classes of compounds decreased by as much as 30 to 50 percent.

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