Barrels tower overhead in the storage area of One Eight Distilling in Washington. Most of them are new white oak, but others are darker with age and use, each labeled to denote what liquid — sherry, muscat wine, rum — it used to hold. What’s quietly happening here and at distilleries around the world is the aging of spirits. For a harsh corn whiskey caterpillar to become a caramelly bourbon butterfly, it has to metamorphose by cocooning up in wood.
The technique likely started by accident. For centuries, the wooden barrel was a chief means for moving goods over distances. Well before forklifts, it allowed people to move massive weights by rolling the barrels, container and wheel all in one.
It’s unclear exactly when people began charring barrel interiors, but they probably did it to get rid of flavors from whatever the barrel last held. At some point, they noticed that wines at the end of their journey tasted better than at the beginning.
Centuries later, barrel aging is an art and a science that wine and spirits makers invest money and time into getting right. The influence of wood is even stronger in spirits, whose higher proof makes them extract more of the botanicals they rub up against. Estimates vary, but anywhere from 40 to 70 percent of the flavor of an aged spirit is thought to come from the wood.
Globally, several species of European and American white oak remain the preferred material. “They’re able to breathe, so oxygen can pass in and out of the barrel — which is a key component of maturation — and they taste good,” says Jason Stout, vice president of marketing and business development at Independent Stave, an international cooperage company founded in 1912 and headquartered in Missouri.
The main difference between a barrel the company would create for, say, a bourbon and one for wine is that a bourbon barrel will be charred inside rather than gently toasted.
What happens to a spirit during its years in a barrel is multifold: Unappealing flavors get filtered out by that layer of char. New flavors get put in as the alcohol penetrates into the so-called red layer underneath the char and extracts its chemical components. As temperature and humidity levels change around the porous barrel, it “breathes,” causing evaporation and oxidation inside: Some of the liquid disappears into thin air while the spirit is maturing (the fabled “angel’s share”), but the interaction between wood, spirit and air also impacts the development of flavors.
“Wood is made of certain building blocks . . . and heat transforms those big building blocks into smaller compounds that are then extracted,” says Stout. Understanding how to get those flavors out is part of the cooper’s art. You might be trying to get at, for example, an aldehyde called vanillin. “How do we toast that barrel in order to . . . get the maximum amount of vanillin?” says Stout. “Or how do we create a little bit of that sweet smoke character, without going a little too far and starting to get into that kind of burnt smoke character?”
Distillers can do plenty of experimenting, but what they can release under particular designations is another story. In the immortal words of Walter Sobchak, there are rules, man. American “straight bourbon whiskey,” for example, must be stored in charred new oak containers for no less than two years. Irish whiskey regulations specify the length of time in barrel, but not the type of wood. Cognac regulations specify the type of oak and the time the spirit must stay in it.
While those few oak species continue to dominate globally, they aren’t the only ones used. In Brazil, makers of cachaça have experimented with native woods, and their exploration has been influential. The culture of Scotch whisky is known for its devotion to tradition. When the country’s whisky regulations were rewritten a while back, Bill Lumsden, director of distilling for Glenmorangie, a distillery founded in the Scottish Highlands in 1843, knew he was part of the reason.
Intrigued by the work cachaça makers were doing, “I had some barrels made of Brazilian cherry wood, and somehow the Scotch Whisky Association found out about this and called me into their offices and told me I was a naughty boy,” he recalls. The regulations at the time were a bit unclear, he says; they were soon tightened to specify that oak, and only oak, could be used in the aging of Scotch.
While Lumsden plans to continue to experiment with other woods, he won’t be allowed to call any of it Scotch. And he’s okay with that. “I have to say, the results of the cherry wood experiment were truly terrible.”
What a spirit will glean from a barrel isn’t always just from wood. Remember those darker, used barrels in the One Eight warehouse? A spirit that goes into a barrel that previously held something else will get less from the wood (the first liquid has already sucked some of those flavors out), but will get flavor from the previous contents.
This is one of many differences between bourbon and Scotch: Where bourbon has to be aged in new charred oak, the Scots generally reuse barrels that have held wine or other spirits, so the wood typically has a more subtle impact. (It’s sometimes too subtle for John Glaser, founder of Compass Box Whisky, which focuses on striking blends. “The quality of the cask is paramount to making great whisky,” he told me via email. Some other Scotch producers, he says, use casks that have been used four or five times. “They’ll be devoid of much in the way of flavor compounds at that stage.)
In the craft world here in the States, small distillers are doing all sorts of interesting things with cask finishing. Regulations give plenty of flexibility in how you may “finish” a spirit in wood, and if you don’t care about releasing a spirit under a recognizable category (bourbon, for example), you have room to play around from the start.
On Iterations 3 and 4 of its Untitled Whiskey series, each of which is different in blend and barreling, One Eight loaned ex-bourbon barrels to Vigilante Coffee; the company stored roasted and unroasted coffee beans in them; later, One Eight took back the barrels for finishing whiskey. It has done a similar experiment with chocolatier Harper Macaw.
In partnerships with makers, breweries, cideries and rum makers, “we both end up with wonderful products,” says co-founder and head distiller Alex Laufer, because their partners end up making something with the ingredients they’ve stored in One Eight’s barrels.
Even with so much now known about what happens to spirits during the aging process, so much science behind it, some of the pleasure is in the remaining mysteries.
“We did a collaborative whiskey with the Whiskey Library,” says One Eight CEO and co-founder Sandy Wood. “It’s just two small rye barrels. Same mash, same distillation, they were kept side by side and have been for two years. And they are very different both in proof and flavor. It’s all about the differences in the oak.”
Whatever you love in aged spirits — the creativity and surprises that come out of craft barrels, the iconic bottlings from famous distillers, the cocktails you can make from them — wood is part of the pleasure. Consider it one more reason to hug a tree.
Bottles to try
Avuá Cachaça’s native wood aged bottles
Compare the Prata (rested in steel casks) with bottles, such as Amburana, that have spent time in native woods.
One of the distillery’s casking experiments with Quercus garryana
, an oak species native to Seattle.
Glendalough’s 13-year-old Single Malt Irish Whiskey and 13-year-old Mizunara Cask Finish
If you can find a bar that has both of these whiskeys, try them side by side for a sensory education on the difference that can come from some extra time in a different kind of oak.
The embodiment of Compass Box’s innovative whisky blends. If you can find someone who has an older bottle, compare — Compass Box altered its original aging method (using inner staves of French oak) when the Scotch Whisky Association challenged it.
Glenmorangie’s Discovery Set/Sampler Pack
The original flagship 10-year-old Glenmorangie single malt, along with three other bottles — the La Santa, Quinta Ruban and Nectar D’Or — containing the same whisky after it has spent two more years in containers that previously held sherry, ruby port and sauternes.
St. George Spirits Baller Whiskey
Aged in ex-bourbon, French wine casks and a final rest in casks that held umeshu plum wine liqueur.
Virginia Distillery’s Cask Finished Virginia-Highland Whiskeys
A blend of Scottish malt whisky and younger American single malt. The distillery has done finishes in cider, sherry, rum casks and more; the port cask edition is a standout.
Amrut Naarangi Single Malt
It spent time in a barrel that held sherry and orange peels, resulting in subtle (not cloying) orange notes, with some nice wood and spice notes mixed in.
Aged in both ex-bourbon and ex-sherry casks. You can taste the influence of both.
Copper & Kings’ brandy Craftwerk series
Aged in barrels from craft breweries around the country, pulling flavors of the various beers into the brandy.
Allan is a Hyattsville, Md., writer and editor. Follow her on Twitter: @Carrie_the_Red.