Charcoal mellowing (or the Lincoln County process)

Probably the most popular and best-selling American whiskey in the world is made according to the prescribed law in the classic way as bourbon. However, the fresh distillate, White Dog to the Americans and New Make to the Scots, undergoes an additional filtration step before it can mature into Jack Daniel’s in charred virgin oak casks.

Who invented charcoal mellowing

Alfred Eaton is generally credited with inventing the charcoal mellowing process in 1825, commonly called the Lincoln County Process “named after the county in which the original Jack Daniel’s distillery was located”. Most sources dispute this however as the process previously called charcoal leaching has been used as a process for thouasands of years and was part of how Nathan ‘Nearest’ Green taught Jack Daniel to make whiskey.

How does charcoal mellowing work?

The white Dog runs through a column filled with sugar maple charcoal, which removes a large part of the rough aromas and results in a softening of the distillate. This process is therefore also known as charcoal mellowing. This process was granted geographical protection by the law of the state of Tennessee in 2013 and is still practiced by distilleries such as Jack Daniel’s and George Dickel. Put simply, Tennessee Whiskey is a bourbon plus maple charcoal filter, made and aged in the state of Tennessee.

How is the charcoal prepared?

The charcoal required for this is obtained by burning the wood of the sugar maple tree. After drying in the air, the felled trees are cut into about 1.5 meters long, cuboid planks with an edge length of about 10 cm. These are then placed crosswise on top of each other in stacks up to 1.5 to 2 meters high. Usually four such stacks are arranged in the shape of a square and with a slight inclination of each individual stack into the inside of the square, so that it can collapse inward when burned. The piles of wood are then showered with alcohol - at Jack Daniel’s they use spirit with an alcohol content of 140 proof (70o / o) - and set on fire. The fire is controlled by spraying it with water, which is supposed to prevent the formation of ashes. The burning process takes about three hours, and after cooling, the charcoal is broken into smaller pieces. This fills the vats with a diameter of about 1.5 meters, the so-called Mellowíng Vats, 10 feet (3 meters) high and guides the White Dog through the charcoal layer from above, following the force of gravity. At Jack Daniel’s There are 84 such Mellowing Vats, which have to be refilled about every six months They are responsible for the fact that Dickel claimed at the time that his whiskey always tasted softer if it was made in the colder months of the year.

Over time, each manufacturer has established its own method, so there are different variants of the Lincoln County Process:

• Jack Daniel’s uses a layer of charcoal about 3 meters thick. The whiskey is trickled onto this layer and over time seeps down through the charcoal. The particularly gentle gentleman Jack even goes through a double filtration (charcoal mellowing).
• George Dickel, on the other hand, uses a layer of charcoal around 4 meters thick. The whiskey is cooled beforehand and completely soaked in the charcoal, which should enable more intensive filtration.

What does this additional filtration do?

The sugar maple charcoal produced using this procedure has a surface area of ​​around 300 square meters per gram and removes a certain amount of congeners but by no means all from the white dog. When interacting with charcoal, larger molecules are removed through adsorption, i.e. through the accumulation of substances in liquids on a solid surface. These are mainly fusel oils (mainly branched and higher alcohols), esters and unpleasant-smelling sulfur compounds such as dimethyl trisulfide. As a result, a lighter spirit remains after the filtration, which then reaches the barrels for maturation. Scientific studies recently showed that the sugar maple charcoal had removed a third of the branched alcohols and almost half of the ethyl esters and that the distillate tasted smoother and less harsh than the unfiltered product using the Lincoln County process.

A subtractive process

However, this also means that the charcoal reduces the fruitiness in the distillate when the esters are removed, as these compounds are largely responsible for the fruity aromas of apples, pears, peaches, bananas and berries. Filtration is therefore a subtractive process that softens or smoothes the taste of the distillate, but technically, and in line with the legal requirements of bourbon the process does not add any taste. The Lincoln County Process is associated with a loss of about 1% ABV (alcohol by volume). Treating spirits with charcoal is not only common in Tennessee whiskey, but is also used in the manufacture of vodka. The main difference, however, is that when filtering vodka, activated charcoal with a significantly larger surface area of ​​up to 1,500 square meters per gram is used, which adsorbs almost all of the aromas from the distillate, leaving behind an almost odorless and tasteless spirit.