From the largest names in bourbon to the smallest craft distillery the one uniting factor that ties them all together is wood, and oak in particular. Absent the mighty oak tree, bourbon would not be bourbon. It would be transparent, fiery, and lack all of the flavors that we all have come to enjoy unpackaging in conversation amongst friends in our garage bar or bellied up with a Glencairn at a local watering hole.
There's a whole complex history surrounding bourbon barrels that few take the time to truly understand. Like for instance, the reason we use "new" charred oak barrels was in part shaped by the need to put men to work during the Great Depression, of course it also helps with the consistency of the resulting spirit. In today's post however let's delve into the art of wood and understand a bit more about the impact wood has on the bourbon we all enjoy.
When it comes to oak species used for bourbon barrels, white oak (Quercus alba) is the go-to for most distilleries. White oak makes sense to use as it is a fairly common oak species found extensively in bourbon country with a distribution that runs from Minnesota to Texas and hits every state east of there. Interestingly enough, there are approximately 90 different species of oak here in the US alone. Nothing in the standards of identity says that thou shalt use any specific species of oak however and so you will find a number of other oaks used at times in the making of bourbon with a worldwide speciation of nearly 500. The Old Charter Oak line from Buffalo Trace is a great example of how distilleries have used other species of oak from around the world. If you've got 3 extra minutes, there's a post on their Chinkapin Oak Barrel Aged Bourbon as a part of that lineup.
In the case of Brown-Forman, oak is brought in from three different regions, the Appalachians, Ozarks and northern forests which showcase varying characteristics because of the regionality of the growing conditions encountered. This includes changes in climate, sunshine, soil conditions, rainfall, etc. These types of variation lead to things like lower density and higher porosity, higher levels of compounds like lignin derivatives which impart typical bourbon flavors of vanilla, caramel and chocolate, etc. To make up for these natural nuances, the Brown-Forman coopers work to blend wood together to create their barrels putting forward a more uniform profile.
Although the thought of breaking out your salt and pepper shaker is likely the first thing that comes to mind, seasoning of wood for bourbon barrels is a time intensive investment, that can be shorted with a kiln but doesn't yield the same results. Seasoning is typically accomplished by exposing the wood to the elements for a period as short as half a year to as long as two years and in some cases even longer with the intent to be drying the wood to an acceptable level given the water content of a newly felled tree. When seasoning outside, the elements go to work on the wood as well as naturally occurring microbes which break down compounds in the oak that will then be imparted to the bourbon during maturation. Kiln drying does not provide the same...you simply have workable wood ready for the cooper.
Beyond the requirement to use new barrels for aging bourbon, those barrels are also required to be charred. Charring can range from a light burning to a much more robust burn that leaves the inside of the barrel looking something akin to alligator skin. Depending on the brand or distillery, there are various specifications for this. Despite its small size, charcoal has enormous surface area --- 1 gram of charcoal has approximately 2,200 square feet of surface area!!!! Not only does this layer impart the beautiful brown color associated with the whiskey we love, but it also latches onto undesirable aromatic compounds like sulfur keeping them from making it into our dram. Further, with the wood opened up if you will, allowing for greater penetration of the spirit into the wood, this complex interaction catalyzes the ability to extract key flavors and with time serves to drive chemical changes that are essential to modern bourbon.
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