I find it strange to think, but the life of a bourbon barrel is fairly complex and in large part has been shaped by the need to put men to work during the Great Depression. In 1938, the United States mandated that bourbon must be aged only in new barrels. This practice was put in place, in part, to create work for loggers cutting down trees and coopers making said bourbon barrels but certainly helped to also regulate the quality of modern bourbon whiskey. Generally speaking, some distilleries had already adopted this practice of using new barrels given that each run of a barrel saw diminished flavor profiles. When consistency is king, reusing barrels just doesn’t make good business sense.
As Prohibition subsided and the Depression was in the rear view of the country, distilleries ramped up their production to attempt to meet demand. Then came World War II. When the U.S. joined the war in 1941, alcohol was needed to manufacture ammo and synthetic rubber. Distilleries shifted their scope from producing bourbon to wartime feedstock, making high proof alcohol which allowed for the production of ammo and rubber, mentioned above as well as things like antiseptic, anti-freeze and more.
Despite the “freeze” on producing whiskey for consumption, distilleries were still working through barrels from their rickhouses to supply the whiskey that the general populous needed. After the war, distilleries had amassed large quantities of used barrels, which now by law, had no commercial use. It was during this time that the Scottish (and Irish) saw value in the used American barrels and began purchasing them for use. Given that laws here in the United States restrict a barrel’s useful life they in turn create a market for barrels that stretches the world over.
Today, thousands of used barrels find a second life across the pond in Scotland where they are reassembled and used to age Scotch Whiskey. Something like nine out of ten casks have origins here in the United States. Given that each barrel retains maybe five percent of the juice in the wood, one could say that many bottles of scotch have a little bit of bourbon in them by the virtue of using the barrels.
Making Bourbon Barrels
By law, barrels are to be new, charred, and made from oak, with white oak (Quercus alba) being typically utilized as it is a common species that occurs through the midsection of the country. When a tree is fell, it has a moisture content somewhere near fifty percent. Once the tree milled and cut down into boards, they are dried, and sometimes matured depending on the distillery to achieve a significantly lower moisture content and in the case of maturation, more unique flavor profile for the wood. When one matures white oak, there is a reduction in tannins which means less bitterness in the resulting spirit.
The average white oak tree used for making a barrel is 100 years old and produces about two barrels. In 2020 nearly 2.5 million bourbon barrels were filled. Ideal white oak spacing yields about 140 trees per acre. Assuming 1.25 million white oak trees are needed to satisfy yearly bourbon demand, that means that nearly 9,000 acres of forest are fell each year. Imagine an area of forest the size of city of Owensboro, Kentucky disappearing each year all in the name of bourbon!!
Staves are then made through milling of the cut boards into a trapezoidal shape following cutting of the boards to ensure the grain (growth rings) are oriented properly which increases stability and minimizes leaks in the barrels. It is at this point that a barrel is ready to be raised. A little more than thirty staves go into making each barrel and the barrel raiser will place these evenly within a temporary steel ring while shuffling the pieces to ensure an even distribution of wide and narrow staves. Once complete, the loosely assembled work in progress of a barrel is inverted and steamed. After this steaming, the staves are now flexible enough to add another steel ring around them and for the first time in the process, actually kind of looks like a barrel!
Bourbon Barrel Charring & Toasting
Once fully assembled, a barrel may be toasted, must be charred (by law) and at times is both toasted and charred. Toasting of the barrel introduces heat at a specified temperature which liquefies sugars in the wood and causes the barrel to expand. During this process, the sugars in the wood move towards the surface and caramelize which then imparts a lot of the flavors and color you recognize in your whiskey. Toasting is not a requirement for barrels, though many do it, whereas charring is a requirement by law for any bourbon barrel. Although toasting goes deep, charring only touches the surface and creates a layer of charcoal that serves as a filter, helping remove unwanted flavors and compounds.
The Finishing Touches of a Bourbon Barrel
There are the obvious other parts of the process, making the head of the barrel, forging the hoops, hooping the barrels, and drilling the bunghole but these aren’t nearly as involved as creating the staves. Once it is all complete, a gallon or so of water is poured into the barrel and rotated to wet all the staves and head pieces. Pressurized air is then introduced to see if any water is forced out of the barrel, seen as bubbles – if not, it’s good to go, if so, it’s back to the cooper station to repair. It is important to keep empty barrels moist either with water or with whiskey as a dry barrel can be subject to shrinking and will leak like a sieve.