When it comes to American whiskey (or bourbon), a tremendous amount of the flavor you taste in your glass (as much as 60%) comes from the barrel that the whiskey was aged in. As a result, the time and attention that whiskey manufacturers like Jack Daniel’s Tennessee Whiskey put into making that barrel is extremely significant. Drink Spirits had an opportunity to go behind the scenes at the Brown-Forman Cooperage in Louisville, Kentucky to see firsthand how these barrels are made.

The Brown-Forman Cooperage is the only barrel making facility exclusive to one distiller. Formerly the Blue Grass Cooperage Company, the cooperage was renamed in 2009 to the Brown-Forman Cooperage. The facility makes barrels for all of the Brown-Forman barrel aged spirits, including Woodford Reserve, Old Forester, Herradura Tequila, Collingwood Canadian Whiskey, Early Times Bourbon, and of course, Jack Daniel’s Tennessee Whiskey. The scale of the facility is massive, including an aging and storage facility for the wood that goes into making the barrels that has over thirty million dollars worth of lumber stored in it.

Barrels made at the Brown-Forman Cooperage are all made from American Oak. Wood is sourced from a number of regions, including the Ozarcks, Appalachia, and a “Northern Region” that includes and surrounds Minnesota. The wood from the various regions is milled and then delivered to the cooperage. Fresh cut oak, or “green wood,” is 85% water, so to be used for barrels it needs to be dried and aged. Drying wood too quickly can create splits, cracks, and checks (microscopic cracks) which cause a barrel to leak, so the wood needs to be slowly aged outdoors. The green wood is stacked fifteen to twenty feet high in an outdoor stockyard for nearly a year. Each whiskey has its own barrel recipe that dictates how long the wood is dried and aged; for example, Woodford Reserve is 9 months.

In addition to gradually drying out the wood, exposing the wood to the elements also helps determine flavor. Green wood is high in tannic acids (as much as 12%) which translates into harshness and astringency in a whiskey. When you dry wood outside and it gets drenched with rain and then dried by the sun, this helps reduce and “tame” the levels of tannic acid. There are also fungal and microbial reactions that occur when you naturally age cut wood that unlocks the phenolic structure (which is where the vanilla flavors come from) as well as breaks down some of the wood’s natural carbohydrates. This process imparts many of the fruit, spice, and sweet flavors and aromatics that make their way into the final whiskey.

After being exposed to the elements, the oak is then relocated into giant heated warehouse kilns where they are exposed to high heat to finish the drying process. The amount of time that the wood may stay here again depends on the barrel recipe (which are all proprietary). The wood is mixed so that the final barrels are all a blend of the various sources of woods, which helps create a uniform flavor.

After the wood has been aged and dried, it makes its way through a number of steps in the cooperage on the way to becoming a barrel. The first series of steps are to transform the wood planks into the staves and heads of the barrel. Getting this process right is important as these barrels need to be water tight: imperfections or mistakes here lead to leaks later on in the process.

The heads (or ends) of the barrel are made by pinning together planks of wood and then cutting them into a sphere. These heads are charred separately from the barrel and then affixed towards the end of the process.

Barrels are built by hand one stave at a time. A worker at the Brown-Forman Cooperage will assemble 500 barrels a day with over 2,000 total barrels produced in a day. Of these, the majority are produced for Jack Daniel’s.

After the barrels are built, they go through a multi-step process to get them ready for making whiskey. The first step is called toasting. The barrels are slowly heated on the inside to around 450 degrees. The amount of time they toast the barrels is a trade secret, but the toasting helps break down the natural occurring aldehydes including vanillin which get released into the whiskey during aging. Brown-Forman is one of the only cooperages to toast their barrels before charing them, and this extra step is one of the reasons why their whiskies have such nice vanilla notes to them.

Jack Daniel’s barrels go through the char process

Once the barrels are toasted, they are ready to be charred. Charring barrels is one of the most dramatic and exciting parts of the barrel-making process. Open ended barrels are placed over natural gas burners and set on fire, exposed to heat as high as 1500 degrees. How long a barrel is exposed to these flames determines how deep into the wood the char goes. Char is measured on a four level scale with the deepest char, #4, called alligator char (as the staves look a lot like the backs of alligators after this deep char). Charring a barrel breaks down the hemicellulose in the wood into sugars, which get caramelized and impart the sweet caramel flavor into the whiskey. The charred wood also forms a thin layer of carbon which significantly helps reduce the oiliness from the corn spirit used to make bourbon and whiskey. Ultimately, charring a barrel makes many of the elements from the barrel more accessible to the aging whiskey, as some of the elements are water soluble and some alcohol soluble (the proof of the spirit that goes into the barrel can dramatically impact the elements it can access from the barrel).

After a barrel is charred, the heads are added to each end, a bung hole (where the spirit goes in) is cut, and then the barrel is filled with water to check for leaks. Any barrel that leaks is then fixed by a small group of coopers who replace staves, fill cracks, and and fix bands. A small leak could mean losing a lot of whiskey over the aging process, so this final testing phase is crucial.

Once the barrels pass the testing, they are shipped off to Lynchburg, Tennessee where they are filled with new make spirit that ages to become Jack Daniel’s Tennessee Whiskey (or, for Woodford Reserve and Old Forester, they stay in Kentucky).

One of the things you realize watching a Jack Daniel’s Whiskey Barrel being built is how natural a process it is. While there’s a fair amount of machinery in the cooperage, the process all is focused on shaping and preserving the natural qualities of the wood. “Each barrel is as individual as one of us,” remarks Master Distiller Chris Morris, and it’s amazing how any spirit company can make a uniform whiskey using barrels that are all unique. There’s something magical about the process of turning planks of wood into whiskey barrels, and I’m glad we got a chance to see the process.

The Brown-Forman Cooperage can be toured as part of Mint Julep Tours.