It’s easy to sit back with a snort of your favorite bourbon and completely take for granted the full depth and breadth of what it has taken to impart the flavors you are enjoying. From the random acorn a squirrel buried for winter and forgot that then sprouted and spent close to a century growing in the forest to turn into the barrel used to age your bourbon, the corn crop carefully planted by an American farmer after working the ground and hoping for just enough rain – but not too much that lent itself to the mash bill, or the years in the wood that the heart cut of the distillation process spent aging drawing color and flavor from the wood, a number of key variables all come together to make bourbon whiskey.
The most significant factor which we’ll focus on today in determining the flavors imparted in your dram is the interaction between the portion of the distillation process known as the heart cut (the liquid that makes its way to the barrel) and the chemicals in the charred barrel’s wood. It’s been suggested that this interaction equates to approximately seventy percent of the final flavor profile of the bourbon. Although there’s no minimum for how long bourbon needs to stay in the barrel, it is broadly accepted that with more time spent in the wood, bourbon becomes smoother and better to drink – to a point – with the sweet spot being often around five to ten years for many bourbons. It’s not always that easy however, and often depends on a lot of factors like placement in the rickhouse, barrel size, climatic conditions, etc. etc. etc.
When it comes to barreling, by law, bourbon must be aged in new, charred, oak barrels. White oak (Quercus alba) is the most utilized oak species for barrels as it is a common oak species found extensively in bourbon country with a distribution that runs from Minnesota to Texas and hits every state east of there. Most oak trees that are used for barrel staves are harvested when they’re 80 to 100 years in age, and when it comes to bourbon, about ten percent of the annual U.S. white oak harvest goes into barrels. Brown-Forman alone uses around 45 million board feet of white oak each year. To put this in context, a typical oak tree harvested provides approximately 350 board feet, so that would equate to nearly 130 thousand trees. Nothing in the standards of identity says that thou shalt use any specific species of oak however and so you will find several other oaks used at times in the making of bourbon with a worldwide speciation of nearly 500. Probably the most notable brand focused on varied oak species for barrels is Buffalo Traces experimental Old Charter Oak line with releases that now include Chinkapin oak, French oak, Canadian oak, Mongolian oak and just released this past year, Spanish Oak. Mongolian oak is a real outlier on their list as it is exceedingly uncommon given it takes as much as 500 years for that species of oak to grow to a size that’s useable for making casks. Perhaps also why its cost on the secondary is “plus, plus” compared to the others in the mix.
If you’re a Dallas Cowboys fan, penetration is probably top of mind given their inability to stop the run which led to their demise in the playoffs this year. In barrel aging, much like football, penetration of the spirit into the wood can have a significant effect on the output of whether you have a winner, or a loser. The process of charring the barrel is so instrumental in the overall effect of barrel aging. As the barrel is kissed by fire, the resultant charcoal layer, despite its small size, contains incredible surface area. In fact, a single gram of charcoal has approximately 2,200 square feet of surface area! This char imparts color, and latches onto undesirable aromatic compounds like sulfur, filtering these from solution. Recall that when the heart cut enters the barrel it is a clear liquid, but when bourbon exits the barrel it’s no longer clear and given that by law no coloring or additives can be used in bourbon the unique coloration of each bourbon is also derived from the barrel. In the case of 13th Colony’s wildly popular double oak bourbon which according to the Bourbon Blue Book is now fetching nearly seven hundred dollars, its uniquely nearly dark black color has been the recent ire of speculation about additives or dyes. Of course, that’s not the case, and according to 13th Colony, their Double Oak Bourbon is naturally that dark, thanks in large part to “South Georgia weather!”
Beyond the charred layer the heating of the barrel creates what’s referred to as the “red layer.” This layer in the midsection of the barrel stave contains wood sugars which have caramelized due to the exposure to heat. Here in this layer also are lignin’s and tannins which, like the wood sugars, are broken down into other forms. During aging, the distillate breaches this layer as temperatures rise outdoors pushing the alcohol into the wood, then withdrawals during the cooler winter months all the while dissolving these compounds in solution and enhancing the flavor to the whiskey. When you take apart a cask and look at a stave you can view what’s referred to as a “solvent line” which is the visual indicator of how far into the barrel the distillate infiltrated.
While on the rack in the rickhouse water and alcohol can evaporate out of the barrel, often referred to as the “angels share.” Air can also find its way into the barrel, given that barrels are not exactly 100 percent impermeable. As this exchange occurs, oxygen can also interact with chemicals in the barrel creating additional flavors.
There’s lots of nuance as distillers have a myriad of variables they can alter from wood selection, char level, mash bill composition, aging locations, and processes, etc. which all lead to unique outcomes, some good and some less than stellar. The age-old saying variety is the spice of life, certainly applies to my personal view on bourbon, and with thousands of varying bottles on the market all exhibiting the magic that happens inside of a barrel, it certainly feels like for a bourbon lover anyway, there’s no better time to be alive!
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