This is the reason why Jack Daniel's is not bourbon

$1 million worth of wood is burnt annually at Jack Daniel’s.

Darren Lipham and Tracy Matlock have one of the best jobs in the world. They work at the Jack Daniel’s distillery in Lynchburg, Tennessee, and their job, nine times a week, is to build a massive bonfire, watch it burn, then scrape up the leftover charcoal.

One of the stills in action.

That charcoal is the secret ingredient in Jack Daniel’s whiskey and the thing that distinguishes it from American bourbon. It’s used to filter the distillate and the method, started by the man himself back in the 1860s, is known as the Lincoln County Process, after where it began. (A redrawing of county lines now places the distillery in tiny Moore County, which, ironically, has been a dry county since Prohibition).

The company spends $US1 million annually on sugar maple timber – a tree native to New England and upstate New York, about 1600km (1000 miles) to the north – which is piled into ricks (a farmer’s term for a stack) of 5cm x 5cm strips.

Darren Lipham and Tracy Matlock keep an eye on the fire.

Three days a week, three times a day, the pair hold rick burnings, spraying the timber with 140 proof Jack Daniel’s as an accelerant before setting it on fire. Then they stand there and watch it burn, another reminder that whiskey takes time, before extinguishing the flames with water and grinding the charcoal into small pellets.

Whiskey drips into the vat of charcoal

Inside the distillery, the charcoal fills 72 vats, packed three metres deep and the distillate then trickles down through it over three days. That’s a pretty impressive effort when you consider that the distillery produces 530,000 litres (140,000 gallons) of whiskey daily.

The mash for Jack Daniel’s is 80% corn, 12% malted barley and 8% rye. Master distiller, Jeff Arnett, only the seventh person in the role in the company’s 148-year history, says the charcoal filtering removes the grainy flavour and “the stuff you don’t want to be drinking” from the whiskey before it goes into the barrels.

The premium Gentleman Jack is twice filtered for an even smoother finish.

The tasting team checks the whiskey coming out of the vats daily to make sure the charcoal’s doing its job properly and it needs to be changed around every six months, which is what keeps Darren and Tracy busy up the hill at the rick burning.

And it’s this extra filtration that means Jack Daniel’s is Tennessee whiskey, not bourbon.

The charcoal in the vats needs to be changed about every six months.

* Business Insider visited the distillery as a guest of Jack Daniel’s.

Business Insider Emails & Alerts

Site highlights each day to your inbox.

Follow Business Insider Australia on Facebook, Twitter, LinkedIn, and Instagram.