If you're looking to expand your whiskey collection, don't let age be the only thing you pay attention to.
Once upon a time, whiskey aging felt fairly straightforward: The spirit, made from a mash of grain, was distilled and then sent to repose for a short or long period of time in a wood barrel, usually oak. There are laws that dictate the specifics of those barrels in some places. But for a long time, the barrels that the white spirit entered were generally the ones that most whiskeys spent the entirety of their time maturing in.
That’s no longer the case. Today, whisk(e)y producers around the world are experimenting more and more with different types of barrel sizes and origins, with special barrels for finishing, with novel methods throughout the process.
And while the finishing barrels seem to get the most attention these days – Angel’s Envy has been one of the historical leaders among American whiskeys in this realm, and now, it’s become far more commonplace throughout the industry – it’s not just the finishing barrels that impact the final whiskey. I reached out to a number of whiskey professionals around the world to try and wrap my arms around what’s so important about aging whiskey, and what the most critical parts of that process are.
What impacts how a whiskey is aged?
“There are a lot of ‘things’ going on inside the barrel, some of which are time dependent, some of which are temperature dependent, some of which are related to the oxygenation,” explains Paul Hletko, Founder and Master Distiller of FEW Spirits. He adds: “There are so many variables that picking just one or two to focus on is challenging and oversimplifies.”
At its core, both the composition of the spirit and the ways in which it interacts with the wood are central. “Both the mash bill and the level of char inside the barrel will have significant impacts,” notes Bruce Russell, associate blender of Wild Turkey. “The level of corn, malt, and chosen flavoring grain will directly impact what flavors develop during maturation. The char level will determine how deep the whiskey can penetrate the wood, and impacts the amount of color the whiskey absorbs. Toasting a barrel can impart more vanilla notes, and many distilleries will both toast and char their barrels.”
Related: How to Store High-End Whisky
Barrel composition and production
There is a real art to finding the best barrels as they age, because the process of maturing doesn’t necessarily happen in a smooth progression—this is part of what makes older whiskeys like the Maker’s Mark Cellar Aged (a blend of 11- and 12-year-old whiskeys) and the Knob Creek 18 Year so special. “Interestingly, barreled whiskeys have ‘sweet spot’ ages. It isn’t a linear process, though, and each barrel will be different,” noted Mark McLaughlin, co-founder of Old Line Spirits. “For example, we’ve had certain barrels peak at [a] certain age, fall into the doldrums for a bit, only then to peak again in a totally different way later. It’s really interesting. So while age is a very important factor for aging whiskey, older is not always better. Harvesting the right barrel at the right time to achieve the desired profile is an art, and age is one of several factors at play.”
The ways in which the barrels are exposed to heat also affect not just the final liquid’s character, but also its chemical composition. “The level of toast [or] char the wood receives allows us to use the same type of wood (eg. European or American oak) and achieve a different flavor profile,” adds Bushmills Master Blender Alex Thomas. “Toasting or charring opens up the wood, which makes it easier for the spirit to get in…The charred wood also acts as a filter, changing or eliminating various congeners in the distillate. Congeners are substances produced during fermentation, other than ethanol, and can be both good and bad. Distillation takes care of many of the bad congeners and the barrel removes the rest. This variation in toast time and temperature, as well as in char level, create different flavor profiles.”
Ambient temperature and environmental factors
Eddie Gonzalez, head blender of Wolves Whiskey, adds that the temperature of the environment in which the barrels are resting also impacts how the whiskey travels in and out of the wood as the barrel expands and contracts, pulling more flavors into the whiskey as it ages. “The size of the barrel [also] changes the surface area the liquid has to work with, which affects how much wood influence there may be on the spirit,” he explains. “Whether the barrel is new or used, and what it held before, impacts the whiskey in incredible ways.”
Temperature can also be leveraged in unexpected and impactful ways. “Most barrels are standardly kept between 35 and 46°F in winter and 57 to 68°F in summer,” explains Ewan Morgan, national luxury ambassador for DIAGEO. “However, extreme temperatures can be used to influence the liquid character. For example, this year’s Talisker Glacial Edge 45-Year-Old was made from twelve heavily-charred American oak casks that were exposed to sub-zero temperatures for 96 hours in the Canadian tundra. This allowed the extreme cold to fracture the wood, increasing the surface area of the casks and altering the liquid’s interactions with the casks during the finishing period in Scotland.” DIAGEO has an annual set it calls the “Special Releases”, which consists of eight cask-strength standouts that represent a fascinating deep dive into the impact of aging and finishing on a range of whiskies.
Environmental factors also affect the interaction between the whiskey and the wood—even where specific barrels are located in the rickhouse. “The location within the rickhouse plays an important role on how whiskey matures,” noted Danny Polise, co-founder of Penelope Bourbon. “Rickhouses come in all shapes and sizes, even material. Metal, brick, concrete, and wood types all create unique microclimates within their structures. Wood and metal rickhouses have great fluctuations in temperature throughout the day when exposed to sun, whereas brick and concrete rickhouses tend to be more stable in temperature. Temperatures between lower floors and upper floors can have up to 15 degree temperature variation, and with that the profile of the whiskey can start to become very different between two barrels of the same distillate in two different locations. Because of this, it's important to taste through barrels in all locations and blend accordingly to create the best product you can make.”
Some producers have found that individual rickhouses stand out enough to warrant their own bottling. “On our distillery grounds, we have three aging locations,” Wild Turkey’s Bruce Russell pointed out. “I particularly like the whiskey being aged at our Camp Nelson site, as the property maintains good air flow and the rickhouses receive a lot of sunlight. So a hot, dry, airy environment seems to work well for us. We’ve seen this reflected in our recently released Russell’s Reserve Single Rickhouse offerings, both of which came from the Camp Nelson site, with bottlings from Rickhouses C and F, respectively. These whiskeys showcase and celebrate the impact of the whiskey’s aging environment over time.”
Dan Crowell, US brand ambassador for Glenmorangie, also pointed out the importance of other environmental factors. “In a northern temperate zone like Scotland, the temperature variance between summer and winter is less than one would find in more southerly climatic conditions like those in Kentucky. So cask positioning in a maturation warehouse in Scotland will have a reduced differential impact on the maturing spirit than it would in Kentucky.” He added: “The change in pressure inside the cask, the expansion and contraction of the staves themselves, and the change in relative humidity that accompanies the overall temperature gradient will all have an impact on maturation. As a result, those casks positioned on the lower floors closer to the center of the structure would mature more slowly than the casks nearer the exterior walls, particularly on the higher floors.”
Of course, the amount of time a whiskey spends in barrel cannot be overlooked, though it’s important not to over-do it. According to Meghan Ireland, Chief Whiskey Blender for WhistlePig, “While the whiskey isn't going to go bad [after an extended period of time in the barrel], it can start to pull flavors you may not want at a certain age. The longer it sits in a barrel the more wood flavors it takes on. Whiskey will also oxidize over time. Neither of these things are necessarily bad, but every palate is different.” The best blenders monitor this, and harvest or blend barrels accordingly.
The Jefferson’s Ocean Series famously takes the proverbial rickhouse on the road, as it were; they age their whiskeys at sea for a time, exploring the ways in which temperature and humidity variations, as well as the sloshing and subsequent micro-oxygenation of the liquid itself, affect the final product.
Do alcohol levels impact how a whiskey is aged?
There also is the issue of how much alcohol is in the spirit when it hits the barrel. “Most of the bourbon industry enters the barrel at the legal maximum of 125 proof; this saves on cooperage costs, since fewer barrels are needed and the whiskey is diluted as little as possible,” says Jay Erisman, co-founder of New Riff. Conversely, New Riff whiskeys enter the barrel at 110˚. “Our research indicated that not only would we achieve some desirable (more water soluble) flavors out of the barrel at the lower proof, but, critically, the whiskey would show better younger, at the lower barreling proof. This does incur about 25% more cooperage than the higher proof, a penalty we are happy to pay if it leads to superior four-year-old whiskey. It also means our barrel proof whiskies never get obstreperously strong in the barrel, maxing out at maybe 117-118 proof, as opposed to 130-plus proof.”
Nicole Austin, Director of George Dickel & Luxury whiskey, takes a broad view of the impact of aging whiskey. “Certainly, every aspect of whisky production has some impact, from the soil the grain was grown in, all the way through the char of the barrel. But the real question is whether that impact is large enough to generate a perceptible change in flavor or aroma in the final spirit.” For her, the most important aspect of aging whisky is the skill and care of the blender.
In the end, then, trying to distill — sorry! — the ways in which aging affects whiskey, and which aspects are the most important, is an inherently difficult exercise. “It’s kind of like asking which is the most important component of a car — the tires, the engine, or the body?” says Old Line Spirits co-founder Arch Watkins. “It all depends on what kind of car you want.”
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