Why Are the Insides of Whiskey Barrels Charred?

Occum’s razor basically proposes that the simplest explanation is most likely the right one…That it’s best to avoid the more elaborate explanation when possible. While the principle doesn’t always hold up, answers to questions like, “When did whiskey begin being aged in charred barrels” and “What is the history that led to coopers adopting this technique for whiskey making”, deserve a more simplified approach. I think we often miss the obvious answers because they’re not clever. The idea that a cow could light a barn on fire and accidentally char the inside of Elijah Craig’s whiskey barrels is…romantic. A complete load of nonsense, but romantic. Leaving aside the fact that Elijah Craig was NOT Kentucky’s first distiller or that bourbon most certainly was NOT the first whiskey to be aged in charred oak…well, let’s just disregard that story entirely. The truth is that we all prefer a good story to common sense reasoning. Especially when it comes to whiskey lore. The reality is that barrels were charred because wood has always been prone to absorb moisture, rot, and become infested with insects. Charring minimized these issues. Not exactly romantic, but there it is. And the idea that charring is a new concept for the aging of spirits is ridiculous. So let’s look into the reasons for charring and why it ended up being such a big part of American whiskey production.

We first need to consider the fact that American colonists knew a great deal more than they wrote down. When one researches American whiskey traditions, one finds very out quickly that most of the information that would be helpful in understanding traditional distilling methods or give insight into the average distiller’s knowledge of his/her craft was just not written down. Think of your grandmother’s recipes, for instance. Perhaps she took for granted that only she would be reading them. Perhaps she assumed her grandchildren would understand how to properly knead dough in the humidity of the summer or that the butter she was using was made with higher butterfat because she raised Jersey cows on her farm instead of Holsteins. (Jersey cow milk has a higher level of butter fat content than Holsteins- That’s common knowledge to anyone that grew up with dairy cows, by the way.) It is very likely that information couldn’t be passed down in writing due to illiteracy or an assumption that the information would always be passed on through oral tradition. Those that did write down information didn’t record nuanced common-sense details because they assumed the reader doesn’t need that information- it’s common knowledge, isn’t it? The Romans never revealed that they used salty sea water to make concrete, they just assumed everyone would know that you don’t use fresh drinking water for that purpose. Unfortunately, common knowledge is only “common” to the people that share that knowledge. Once the unbroken chain of master distillers, journeymen, and young apprentice distillers was broken by Prohibition, an unfathomable amount of precious common knowledge about the early distilling trade was lost. We can do our best to piece the information together through research, but there are no men or women to interview or journals to read that will explain the answers to us anymore. So…how do we determine the origins of barrel charring? Let’s try to use our common sense and see things from their perspective.

Let’s start with the reality that “charring wood” is not a new concept. Humans started modifying wood with fire around 400,000 years ago. In addition to basic fire-hardening, modern humans routinely burned boat and fence post bottoms to prevent rot and increase longevity. Fire was traditionally used to bend lumber in Denmark, Finland, Iceland, Norway, Sweden, and Japan for boat building. In the time of Vasco deGama (1469-1524), the Portuguese were known to char the outsides of their ships to protect against shipworm. In 1720, the British Royal Navy built a ship entirely out of charred wood called the Royal William. While Europe was dominating the seas through ship building, the Japanese were developing a technique called “shou sugi ban”, or “yakisugi”, to weatherproof the exterior of Japanese homes. Japanese red cedar siding was charred to inexpensively protect houses from the elements, insects, and, believe it or not, fire. It was universally understood that fire and heat can be a tool in mastering woodcraft. The very nature of barrel formation is in the bending and manipulation of the shape of wood staves. People have worked with wood as a building material for literally all of recorded history.

Now that we’ve established that charring wood was recognized around the world for its ability to strengthen and waterproof wood very early on, it stands to reason that “tight coopers” designing barrels that hold liquids would have understood this concept. For nearly 2,000 years, barrels have been the most convenient form of shipping or storage container for those who could afford them. In fact, the Celts were using watertight, barrel-shaped wooden containers as far back as 350 BC! Charring was the easiest way to condition wood to resist rot and insect damage. Wood that may not have been not as water resistant as oak were often charred to improve their ability to hold water.  Softwood such as cedar or cypress and hardwoods like poplar were charred to improve their water resistance. It seems a bit disingenuous to tell modern whiskey enthusiasts that charring barrels could be a modern idea and could be useful in the aging of American whiskeys.

Let’s consider the fact that sea travel by ship was the ONLY method of reaching the New World. The charring of the insides of water and spirits barrels would have been a normal and recognized practice for newly arriving settlers in the New World. The idea that merchants or even passengers would not be familiar with the practice of internally charring water or spirits barrels becomes less likely. While one might argue that an average European may not have been familiar with barrel charring practices, that argument diminishes when you’re talking about seafaring immigrants spending a minimum of two months at sea, each entirely dependent on barrels for their drinking water, beer, or spirits. Preservation was of utmost importance at sea, and no less important on a homestead in the American wilderness. In 1806, an article appeared  in the Journal of Natural Philosophy Chemistry and the Arts, “On the means of preserving water in long sea voyages, and the application of the same means for keeping wines.” The author advises that “The process of carbonizing the inner surface of casks may also afford advantages for the preservation of wines…conjecture that it would become still more agreeable if preserved in casks charred within…Casks which have received this preparation may be used for all the purposes in which liquids are to be preserved.” The article implies that even in 1806, charring was a common practice and that many already understood that using charred casks improves the quality of spirits within even if the reader did not. Kentucky’s Filson Historical Society has letter correspondences on file from 1826 that show American whiskey makers recommending the use of charred barrels to improve the taste and quality of their products. Charring barrels may not have originally been meant to flavor the whiskey, but common sense would tell us that it DID. As with most discoveries, there is no straight line from one person discovering the benefits of charring to the entire country utilizing the practice to benefit their own products. But clearly, people learned, and took advantage of the discovery. But they weren’t just using charring for barrels. Common colonial farming practices involved the charring of wood to preserve it.

An 1861 article in Ebensburg, Pennsylvania’s Democrat and Sentinel local newspaper printed an agricultural editorial column describing the author’s incredulity that he should even need to explain why one should char your fence posts before placing them in the ground: “Really, a post should never be put into the ground in a green state. I need not state the reasons. The end that is put into the ground should not have bark on. Why need I state the reasons? If not cyanized, every post should be charred or burned, at least one-fourth of an inch deep; i.e. so that the charred part shall be at least one foot below the surface of the ground. The New York farmers used to do that, and the posts lasted for life-time. The reason is obvious. While the post is charing, large quantities of water evaporate, leaving the post dry and the pores closed; the charcoal has the power of absorbing large quantities of air gases, rendering it in a measure impervious to water. Finally, charcoal has the power of “resisting putrification of decomposition,” thereby preserving the wood within.” He goes on to explain that everyone has seen how burned logs in the woods do not decay as swiftly as newly fallen logs. The point here is that the common man had an excellent idea of why the interior of a barrel was burned. Moisture introduces the possibility of rot. If you want your barrel to last after it has been introduced to a liquid, you char it. Simple as that.

The modern consensus shared on why whiskey came to be aged in barrels is based on a common understanding that whiskey was shipped long distances over long periods of time. This certainly contributed to the aging and improvement of whiskeys, but it was not a “ah-hah!” moment for whiskey makers. It is highly unlikely that 18th century merchants did not understand and actively take advantage of the benefits stemming from long periods of time passing between the buying and selling of their whiskey. There was a great deal of waiting. Transatlantic shipping and river traffic was part of daily life and bookmaking for merchants. Getting product to distant markets meant navigating creeks and rivers on flatboats and being entirely dependent upon the seasons and the weather to do business. The rainfall/snowfall dictated the price of whiskey in local markets because water levels in the rivers (and later, canals) either meant swift, easy transit for commerce or meant a long wait for the water levels to rise again during dry spells. In the winter, river trade meant dealing with ice dams and hoping they would break up before causing devastating flood conditions upstream. We don’t often consider the seasons and the weather when we make business decisions today, but they were always in the forefront of an 18th century businessman’s mind. Tradesmen gambled on the successful and timely arrival of merchant ships bringing internationally traded items (like liquor). Those highly prized imported goods would then be transported to any number of inland markets by river because the roads were so abysmal. Everyone certainly would have understood that whiskey spent long periods of time in barrels. The average colonist may not have been overly concerned with purchasing aged spirits from their neighbor or in the local tavern, but they were definitely aware of their existence. Whether they purchased imported goods that were warehoused, shipped across the ocean, transported to any number of distant markets by riverboat, or made locally and left to sit in storage until consumed or sold, people knew that spirits changed in the barrel. They may not have understood the science of what happened in that barrel, but they understood that old whiskey was superior to new whiskey. Though this knowledge may seem rather obvious, product pricing reflected this preference for aged products. Time and the seasons determined the course of life for early settlers. Long periods of time in the barrel being resposible for the improvment of spirits was not a foreign concept.

Next, let’s explore the introduction of industrialization to barrel making. Steam power in the late 18th century modernized the coopers craft. By the mid-19th century, Pittsburgh had a barrel making facility that could churn out 100 water-tight barrels a day with a staff of 15 men working $5,000 worth of machinery. Wood staves were now shaped with steam and dried in kilns. While charring may have been inconsistent in barrels that were crafted entirely by hand, factory production would have made barrels more consistent in their construction. Coopers, as contractors of distillers, would have understood what whiskey makers wanted from their barrels. We should not underestimate master craftsmen’s ability to adapt to the use of new technology while maintaining their long standing customers. The practice of charring the insides of barrels was not used when producing oil barrels, but certainly would have been used when making whiskey barrels. Whiskey makers were well-established businessmen by the time industrialization was booming in the United States. They would not have tolerated a reduction in quality in their whiskeys. In mid-19th century Pennsylvania, 42-gallon barrels were the most commonly manufactured size because the average cooperage was employed in producing as many standardized 42-gallon tierce-sized barrels as possible for the newly booming oil industry. Once oil was struck in 1859 in Titusville, Pa, rye whiskey producers benefited from a reduction in barrel costs due to increased barrel production. By the late 1800s, there is no question that the entire United States whiskey market was using charred oak barrels to age their whiskeys. What is not clear is how well everyone understood what was happening to the whiskey in that charred barrel.

The Guardian. (London, England) December 9, 1826.


An 1870 advertisement in the Wayne County Herald in Honesdale, Pa for “Century White Wheat Bourbon” explained that the New York firm of H.K.Thurber & Co.’s new agent would be offering for sale “A Pure and Unadulterated Stimulant, Unrivaled for Medicinal Use” which was “most carefully distilled from selected stock by the “old copper process” after which it is stored away in charred oak barrels until it reaches a certain age, then it is redistilled by a peculiar process which extracts the fusel oil and leaves the ferment and essential oils of the grain.” Clearly, it was understood that the use of charred barrels to produce superior products was a selling point to the general public. In 1873, Gibson & Son, the rye whiskey behemoth on the Monongahela which claimed to be the largest distillery in the US at the time, was accused of robbing the government of taxes due on whiskey that was “of higher degree than it being was taxed for.” (Talk about free brand PR from the US gov’t!) Tests would not be designed to record the losses in volume due to “angel’s share” or due to “soakage” into the wood by the government until the following decade. The US government excise taxes had never taken into account losses that occurred over time and the distiller had been bearing the burden of those losses. The scientists at Joseph S.Finch Distillery in Pittsburgh began funding its own research into these losses in the 1880s and would later help by sharing their findings with the gov’t to help amend the excise laws. The government finally began to crack down on barrel use by distilleries in the 1880s. By 1889, the commissioner of Internal Revenue issued a prohibition against the refilling of barrels because they began to see profit loss due to the practice. The circular issued by the commissioner read, “the refilling at distilleries of casks or packages previously filled at the same distillery with distilled spirits is hereby prohibited, and all gauging officers assigned to duty at distilleries are instructed to decline to gauge, mark, or stamp such refilled casks or packages, and should such vessels be hereafter presented for gauging, their contents shall be transferred to other packages before being gauged.” Internal Revenue was beginning to understand that losses to the barrels were not just losses to the distillers, but to them as well. They needed answers and began conducting more research into what could be done and what caused these losses. One of the most ambitious government funded studies into barrels, conducted by C.A.Crampton and L.M.Tolman for the Bureau of Internal Revenue, was begun in 1898 and completed in 1907. Interestingly, the experiments conducted by these government funded scientists (combined with those contributions made by many US distilleries conducting their own independent research) show only 2 levels of char were being considered- char and heavy char. Even this advanced 20th century experiment proving that the charring of the barrel is the largest contributing factor in creating the scent and overall character of American whiskey, the level of char was not considered important. In fact, one of the conclusions from the experiment stated: “Acids and esters reach an equilibrium, which is maintained after about 3 or 4 years”… “The improvement in flavor in whiskies in charred packages after the fourth year is largely due to concentration.” And just to throw out some love to Pennsylvania rye whiskey, this conclusion was also drawn: “The rye whiskies show a higher content of solids, acids, esters, etc., than do the bourbon whiskies, but this is explained by the fact that heated warehouses are almost universally used for the maturing of rye whiskies, and unheated warehouses for the maturation of Bourbon whiskies.” (Even the government and the scientists knew that rye whiskey was better!)

There is no definitive answer as to when charred barrels began being used to age whiskey. I think the most realistic answer is to say that American whiskey was a developing art and science in the 18th and 19th centuries. The entire country was constantly evolving as new discoveries and new technologies were applied to the American economy. Whiskey was certainly a driving economic force in the development of early America. As transportation improved, so did the exportation of whiskey to distant markets. I don’t believe that charred barrels were a modern concept by any stretch of the imagination. I do, however, believe that modern concepts have warped our understanding of whiskey history. If we put ourselves in the shoes of those early whiskey makers and begin to appreciate that they had a vast amount of knowledge at their disposal that has been lost, we can begin to give credit where credit is due. The most likely explanation is that the charring of barrels was done to preserve the inside of the barrel, reduce insect damage, and waterproof against leaks. The charring of tight-coopered barrels was likely a common practice for as long as whiskey has been made in America. I do not believe that Americans were instructed by the French and their Cognac/brandy aging techniques as many modern whiskey writers have concluded. Whiskey was not made in a vacuum and its influences come from many spirits manufacturing traditions; wine, beer, brandy, rum, fortified wines, etc. Cognac was certainly not the only spirit that made trips around the world on boats and was not the only aged spirit available to American distillers to draw inspiration from on the use of charred barrels. (Brandy was made each fruit growing season in the colonies right alongside any whiskey production being done and went into the same barrels, so the “chicken and the egg” paradox is at work there.) The French influence upon whiskey as it relates to Louisiana and New Orleans is only applicable to bourbon, which we’ve already established was not the first American whiskey to be aged in charred oak and took its cues from rye whiskey production. Early whiskey drinkers liked their whiskey clear and were slow to accept any color in their favorite drink. Even when aged whiskey existed, most buyers chose clear spirits. The wealthy in America were the first to transition to drinking brown spirits in the early 1800s and the masses would eventually follow suit, but it took them a much longer time to get there.     

It may be that many early distillers did not char their barrels, but those that did produced a finer product which drew more attention in the marketplace. Just as the case is today, the American whiskey world was a relatively small one and it got smaller as time went on and new hurdles were put up to reduce the number of competing distilleries. Competition in the marketplace determined the winners and shaped the products that become successful. Why did most rye whiskey (which was the first American whiskey style to gain widespread marketability- NOT BOURBON) get made in a similar way? Because it sold well. Why did they all use heated warehouses? Because using heated warehouses extracted more flavor compounds from those charred barrels. Charred barrels had established themselves as the best way to ship rye whiskey to markets generations before those steam heated warehouses were developed to squeeze every bit of flavor out of the wood. Because those methods produced a superior product. Because “if it ain’t broke, don’t fix it.” Simple. Common sense.