The type of warehouse a distiller uses is important no matter where the distillery lies on a map. Yet certain regions have developed a preference for one style of warehouse over another, and some have let the realities of the warehouse inform their industry.
Let’s look at the signature traits of Scottish-style dunnage warehouses and American-style rickhouses, then we’ll consider how something viewed as a fault in one tradition can become a distinctive strength in another.
[PAYWALL]
Similar, but Different
In Scotland, particularly, distilleries proudly use traditional dunnage warehouses to age their whiskey. Typical dunnage warehouses include low height, thick stone walls, slate roofs, and earthen floors, and these are distinct as soon as you enter the space.
“The earthen floor means a dunnage warehouse is naturally humid with minimal seasonal weather variance,” says Robin Bignal, distillery production manager at Kilchoman Distillery on Scotland’s island of Islay. The constant temperature and high level of retained humidity are essential factors in a consistent maturation rate for the casks inside the warehouse—both over time, and from one cask to another.
In a dunnage warehouse, barrels or casks are stacked on their sides in “stows”—but no more than three high in each stow, a practice that aims to ensure good air circulation and as uniform a maturation as possible.
In some ways, this is similar to the rickhouses, or racked warehouses that larger American whiskey distilleries prefer, as well as palletized warehouses. The barrels are on their sides in a rickhouse, stacked no more than three high, with plenty of space around the sides and ends of the rickhouse to allow air circulation. However, while the rack may be only three casks high in a rickhouse, the warehouse itself could be many stories tall; rickhouses are generally much taller than Scottish dunnage warehouses. Also, in a rickhouse, barrels at the top of the rack will age at more variable temperatures than barrels at the bottom.
“The casks nearer the top will evaporate quicker,” Bignal says. “In some cases, in higher temperatures, the water in the cask evaporates quicker than the whiskey, resulting in a gain in whiskey alcohol strength.”
As opposed to the specific building materials favored for dunnage warehouses, rickhouses can be made from a variety of materials, including brick, tin, wood, or concrete. For the most part, they lack any artificial climate control, so there are much greater differences of internal temperature within rickhouses throughout summer and winter. Distillers who use this type of warehouse in places such as Kentucky or Tennessee have become especially adept at incorporating the temperature fluctuations into their programs.
While dunnage warehouses offer Scottish distillers an even maturation environment that benefits their style of whiskey, there are also drawbacks to this tradition. The best-known and oft-discussed limitation in the dunnage warehouse has to do with increased labor requirements because of their shape and build. Forklifts don’t fit so easily, so manual movement is often required in part or in whole. That may be a minor inconvenience for a small distillery or one that isn’t focused on huge volume, but it can add up for larger distilleries—though many in Scotland remain committed.
“Also, when it comes to cask selection, it can be more problematic, as whole stows may need to be dropped to get access to the casks on the ground stow,” Bignal says. “Stowing younger casks underneath older casks helps when coming to select casks.” As with their counterparts across the Atlantic, distillery managers in Scotland need to be thoughtful with the arrangement of the casks in the warehouse.
As Bignal says, loss of spirit via evaporation—and the subsequent increase in alcoholic strength—is a serious consideration to anyone in charge of warehouse management. A significant appeal of the dunnage warehouse to Scottish distillers is the mitigating effect it can have on liquid loss. Yet the style of warehouse that American distillers use hasn’t always been so helpful in preventing evaporation, nor has the environment in which they’re located.
When Loss Is a Gain
A 1942 article in the Journal of the American Chemical Society discusses how distilleries at that time were changing their warehousing procedures: “In brief, these changes involved lowering warehouse temperatures from 77° to 70°F [25° to 21°C], maintaining an equilibrium humidity of 65 to 70 percent relative humidity in the warehouse atmosphere, specifying and inspecting new barrels to ensure the receipt of high-quality barrels, and intensifying the maintenance and care of barreled goods during the aging period.”
The article goes on to discuss some of the circumstances that create such an opportunity for loss. They lament the use of wooden barrels, claiming them to be “exceedingly poor containers” from a commonsense point of view, pointing out that losses are impossible to avoid because of the nature of their material. The authors go on to discuss the negatives of wood’s “porous and spongelike” texture—which soaks up whiskey in the same way it soaks up water—and that, on average, a barrel loses 2.4 gallons of whiskey to “soakage.”
Modern producers who read these lamentations from the 1940s now recognize that so many of these “faults” are now praised for their role in the maturation of American whiskey. The American whiskey profile is heavily dependent on the interaction between the new-make spirit placed in the barrel and the porous, spongelike, newly charred oak that it penetrates repeatedly throughout the aging process, as well as the micro-oxidation that takes place because the whiskey is aging in wood. Assessing barrels before filling them to make sure they’re in good shape, ready to hold liquid without leakage, is still a time-honored practice. Yet the American industry has evolved enormously, partly in response to the maturation that is an effect of their chosen style of warehouse.
Distillers in the United States now age their whiskey almost exclusively in warehouses that aren’t temperature-regulated. Barrels filled with new-make from the same run and laid down at the same time can still show wide variation, and producers make use of that. They either blend out those differences to target a consistent profile, or—in an increasingly popular move—they release single-barrel or barrel-pick whiskeys (and the price tends to soar as a result).
When a Bug Is a Feature
The story of American single-barrel culture isn’t complete without mentioning Blanton’s, which claims to have sold the first commercially available single-barrel bourbon in 1984.
As the story goes, master distiller Elmer T. Lee was nearing retirement when he was asked to create a particularly exceptional bourbon. According to the official account from Blanton’s, Lee recalled a time when he worked for Colonel Albert B. Blanton, who, to entertain important guests, “would handpick ‘honey barrels’ from the center cut of [Buffalo Trace’s] Warehouse H and have that bourbon bottled one barrel at a time.”
That was in the mid-1980s; it would take many years for the bourbon industry to snap back in full force—and for the thirst for brands such as Blanton’s to build—but that choice to take advantage of variables caused by warehousing methods has come to define the later era of bourbon. While Scotch certainly has its own single-cask offerings, they are usually a result of an independent bottler. These days, just about any major American bourbon producer has their annual single-barrel sitting next to their flagship on the shelf.
Most of the conditions that those 1940s researchers were looking to reverse—higher internal temperatures, fluctuating humidity, porous wood—have gone from bugs to features in our current bourbon climate. Meanwhile, new whiskey regions are popping up across the United States, touting their (often intense) local weather as an advantage to aging.
Texas certainly comes to mind. When it comes to aging bourbon in the Lone Star state, producers often bring up the diurnal air-temperature changes and how they push the whiskey further into the wood then extract it back out, repeatedly. It’s only a hop-and-a-skip from there to claiming that more of those conditions in a shorter amount of time can result in a faster maturation and darker whiskey coming out of the barrel.
Whether it’s true that whiskey maturation in Texas is indeed “faster,” the evaporation is certainly more significant compared to other regions—thus, most whiskey barrels in Texas top out around four years old. Distillers who go much longer are looking at significant losses that no longer make aging in that barrel viable.
While Scotland has remained fairly committed to its tradition of using dunnage warehouses and to the impacts they have on the character of its whiskey, we’ve taken a different path in the United States. American whiskey distillers have allowed the realities of our warehouses, including the impact of the local climate, to dictate the evolution of our industry—much to its success.
Regardless, this much is true: The style and design of a warehouse is massively impactful to the spirit aging inside. Skilled producers have a clear understanding of that impact in their own houses, and they know how to make the best use of it.
