Yes, Tennessee whiskey is different from bourbon. Inside the law, science and tradition

It’s the question everyone asks: What’s the difference between Tennessee whiskey and bourbon?

The short answer: Tennessee whiskey is bourbon, made in Tennessee, with a key extra step.

Here's what makes Tennessee whiskey special.

The fine print

Though most people think of Kentucky when they think of bourbon, bourbon can in fact be made anywhere in the U.S. According to the federal Alcohol and Tobacco Tax and Trade Bureau, “bourbon whiskey” must be:

• Distilled from a fermented mash of at least 51% corn
• Stored in new, charred oak containers
• Not more than 160 proof when it leaves the still
• Not more than 125 proof when it enters the barrel
• Bottled at no less than 80 proof
• Made in the U.S.

Until 10 years ago, there was no legal definition of Tennessee whiskey. Then the industry, concerned about exploitation, pushed for parameters.

Tennessee whiskey is defined by the state. It must meet the federal definition for bourbon whiskey, plus be:

• Manufactured in Tennessee
• Aged in Tennessee
• Filtered through maple charcoal before aging

The filtration step is named "the Lincoln County process" after the county in which Jack Daniel's sat when it originated the technique. The state later made Lynchburg the seat of a new county, Moore.

There’s one exception to the charcoal-filtration requirement. Prichard’s Distillery was grandfathered in because it had been making what it called “Tennessee whiskey” for 10 years without using the Lincoln County process. Ironically, Prichard's is in Lincoln County.

Additionally, as of 2016, “Tennessee moonshine,” which is very popular in the eastern part of the state, must be distilled in Tennessee.

The science: What is the Lincoln County process and what does it do?

Trent Kerley did his master’s research on the Lincoln County process and now works as a distiller at Sugarlands in Gatlinburg and Kodak.

Charcoal filtering for 24 hours essentially removed a particular category of chemicals, Kerley said: organic acids “that smelled like cheese, feet, vomit.” Treatment also lowered the “malty, rancid, fatty and popcorn” smells, and raised the pH.

That makes sense. The original purpose of charcoal filtration was to make a drinkable product right off the still, back in the moonshine days.

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What happens when that filtered whiskey goes into a barrel? Kerley didn’t have the bandwidth to examine that — the research continues at the University of Tennessee in Knoxville, he said. The differences might blossom. In the barrel, those organic acids react and turn into fruity aromas, Kerley said. Maybe removing some components allows certain reactions to go faster. The higher pH might change reaction speed.

The biggest question for the lay drinker: What difference does this make in the mouth?

Taste and flavor

For decades, there were only two distillers in Tennessee: Jack Daniel's and George Dickel. Their products defined "Tennessee whiskey" as a whiskey with a smoother, sweeter flavor, with some of the edges rounded off.

That comes from two sources. One is the charcoal filtration. There’s a reason Jack Daniel's calls it charcoal mellowing. “It does make a whiskey more approachable,” Sugarlands master distiller Greg Eidam said.

The second source is the grain mash used to make the liquid: high in sweet corn, low in raspy rye.

“I think what defines a Tennessee whiskey, beyond the charcoal, is that low rye content,” Company Distilling master distiller Jeff Arnett said. He used to be master distiller at Jack Daniel's.

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But really, no one knows yet what Tennessee whiskey can be. A number of new Tennessee distillers, including both Sugarlands and Company, are beginning to distill, age, blend or release Tennessee-style whiskeys. They're experimenting with several parts of the process.

Legally, there’s room, lawyer Rob Pinson said. The state doesn't specify how much charcoal to use in filtration or how long the spirit has to stay in contact with it. (For that matter, it requires that the product be manufactured in Tennessee, but that can be as little as diluting a liquor distilled elsewhere.)

Famously, Jack Daniel’s uses 10 feet of charcoal, and whiskey takes three to five days to complete filtration. Sugarlands has a handful of barrels holding charcoal-filtered spirits, Eidam said. The distillery has been using significantly less than 10 feet of charcoal, specifically to keep more of a bourbon character. They're also testing different combinations of grains.

Eidam looked forward to tasting the results.

“You have two big boys who for the longest time defined what Tennessee whiskey is,” Eidam said. “Now we’re going to see what can be done with the Lincoln County process.”

Danielle Dreilinger is an American South storytelling reporter and the author of the book “The Secret History of Home Economics.” You can reach her at ddreilinger@gannett.com or 919/236-3141.