Sat. Jan 28th, 2023
Maureen Stronach, an employee at Diageo's Dalwhinnie Distillery, views whiskey from a cask in the storage room on April 21, 2011.

Maureen Stronach, an employee at Diageo’s Dalwhinnie Distillery, views whiskey from a cask in the storage room on April 21, 2011.

Jeff Mitchell/Getty Images

Almost every distillery tour follows the same format. First, you are guided through a display of raw materials. Then the guide takes you along the fermentation tanks and past the still. But the magic part is what comes next. Once the whiskey is removed from the still, it is put into barrels and stored in cool, shadowy warehouses called rickhouses. The air here smells of the vanilla and oak and the grain of spirit that has evaporated. And since most rickhouses aren’t even connected to electricity, you almost feel like you’ve stepped back in time. Whatever comes from here, it tastes like pure wonder.

In reality, the spell was cast long before you entered these whiskey-scented buildings. Labels, websites and other forms of marketing work together to paint pictures about things like generations of distillers, specific grain blends or the surface details of aging. And on those first steps of a tour, a guide tells a story that’s half myth, half fact, incorporating commonly accepted statistics like the percentage of each barrel that evaporates each year. Despite the lack of published evidence to support such information, these whiskey standards are often repeated as fact, especially by public relations representatives, bartenders and avid consumers.

The truth is that most of the research done on whiskey, especially on how and why it ages, will never be available to the public. With whiskey sales in the US exceeding $2.7 billion in 2014 and expected to continue to rise, producers’ reluctance to share is somewhat understandable. In many cases, the data collected can give any company a competitive advantage.

As this high stakes competition is increasingly met by consumers demanding more products and information has developed into a kind of arms race. On the one hand, manufacturers and scientists are racing to discover what influences the aging process and how exactly it works. On the other hand, an ever-growing number of entrepreneurs are inventing new ways to try and bypass the years it previously took to produce what we would all recognize as whisky.

Fortunately or not, both the old guard and new researchers working on the quick-aging angle are strongly against sharing their findings. And as funding for scientific research dries up every year, outside academic work is unlikely to catch up anytime soon. As a result, compiling a comprehensive overview of what we know about whiskey aging is today largely limited to what producers are willing to share. The resulting story is frustratingly incomplete, but it’s also part of the magic that captivated drinkers around the world in the first place.


Despite the luxury of modern technology, most distilleries continue to use oak casks to age their whisky. As the oldest and most conventional method of aging spirits, time in a cask is usually a legal requirement for whisky. In reality, the definition of what can be labeled as whiskey often varies by country because requirements for cask maturation. Some whiskeys should only be aged in new casks, while others may be kept in previously used casks. As a result, each type of whiskey has slightly different creation parameters and a slightly different flavor profile.

Many countries, including Canada and the countries of the EU, among others, require the spirit to be aged in wood for at least three years. Some others, such as the US, have no minimum age. But beyond those legal requirements, many factors contribute to how a whiskey tastes when it comes out of the cask. LLike many parts of spirits history, the origins of cask aging are so steeped in folklore that the exact story has been lost to history. We just know that it has been standard practice for at least a few centuries. Wherever the idea came from, it’s widely seen today as a way to make the hooch taste better.

The cask’s exact contribution to whiskey is at once obvious (the color and some of the flavor) and extremely subtle. Any distiller will tell you that the cask gives the spirit all its color. In terms of flavor, experts estimate that the barrel adds as much as 60 percent of the finished product’s flavor. But the exact flavors transferred to the drink also depend on the type of wood used to make the barrel.

Tom Collins, assistant professor of wine and grape chemistry at Washington State University, has studied the effects of cask aging on wine and more recently on spirits. In a paper published in 2014, Collins and two colleagues examined the non-volatile compounds — compounds that don’t vaporize in the air — present in 63 samples of different types of American whiskey.

One of their findings was that charring the cask before adding the whiskey releases small aromatic compounds called phenols. “In the unroasted wood, [phenols] would probably have been part of the lignin, the polymer that essentially gives wood its structure,” he tells Ars. Once heated, small amounts of phenols can create depth in the spirit’s flavor and give it smoky or petroleum notes.

During the roasting process, cellulose, hemicellulose and other polymers in the wood’s cell structure break down, Collins tells Ars. These reactions create “sugar breakdown products” that add popular caramel and vanilla flavor notes to the whiskey. “Much of the drink’s character comes from what’s taken out of the barrels and from secondary oxidative reactions that occur,” he says.

Mmm, magical Buffalo Trace.
Enlarge / Mmm, magical Buffalo Trace.

Scott Olson/Getty Images

All about the environment, man

Collins’ work essentially looks at the traditional aging process. Once a barrel has been charred and the whiskey has been distilled, the whiskey is poured into barrels to age. From there it is in the warehouse and natural, seasonal temperature fluctuations cause the whiskey to expand and contract. This movement forces the liquid in and out of the wood. So depending on where in the world the distillation takes place, these changes can be mild (as in Scotland) or vary wildly (as in Kentucky and Ontario).

As any whiskey distillery tour will tell you, no matter where the whiskey is aged, something will evaporate. This is called the angel’s share and the exact amount of evaporation varies by place, but it is said to average around two percent per year globally. That number can be much higher in warmer climates such as in the US and Canada.

But even within a single distillery or warehouse, conditions vary in such a way that they can cause fluctuations in the resulting product. For example, if the building is tall, barrels at the top tend to stay warmer. And as a result, more water than alcohol evaporates from the casks, leaving a whiskey with a higher alcohol content. Close to the bottom it is the opposite: barrels stay cooler. To compensate in either case, many producers rotate their barrels in hopes of evening out the effects of temperature.

The exact effects of temperature and magazine placement on whiskey are difficult to measure. Some distilleries have built experimental warehouses to test long-held theories about how environmental factors affect their whisky. Buffalo Trace’s Warehouse X is perhaps the most famous of these facilities. This research lab has five chambers whose airflow, light exposure and temperature can be 100 percent controlled, says Master Distiller Harlen Wheatley. “We feel like knowing why bourbon tastes the way it does gives you an edge,” says Wheatley. ‘We have five rooms [in Warehouse X]. We test variables in each of those rooms and we’ve seen that all five are different.”

As you might expect, experimenting with these conditions doesn’t always produce salable whiskey. But that’s not the point, says Wheatley. “We’re actually showing that when you change the environment, artificial or natural, you change the bourbon,” he says. “That seems like common sense, but we’re proving theories. What we’re trying to do is put some numbers on it. In other words, how much does it change the bourbon and so on?”

By akfire1

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