The angel’s share is that mysterious bugaboo that endlessly frustrates distillery accountants and causes distillers to cry foul at lost product. A certain amount of spirit goes into the cask, only to later emerge volumetrically diminished.
However, the angel’s share ain’t all bad. In fact, it’s an important component of the maturation process, helping a fledgling spirit along on its journey.
For as long as the wooden cask has existed for the maturation of spirits, so has the angel’s share. Here, we’ll use bourbon as our spirit archetype—but any wood-matured spirit will experience similar phenomena.
Setting the Scene
You’ve got some volume of new-make bourbon diluted down to 62.5 percent—125 proof, the legal maximum for bourbon cask-fill strength in the United States—ready to barrel. You’ve also got some brand-spanking-new 53-gallon (200-liter) barrels made from heavily charred virgin American oak.
Sounds like a better marriage than peanut butter and jelly, if you ask me. So, you go about filling your casks to the brim and set them up for a long slumber in your warehouse. Now it’s time for Mother Nature and Father Time to do their jobs.
A year goes by, and you check in on your maturing whiskey. It’s picked up quite a bit of color and sweetness and, while the new-make character is still there, you can tell that things are heading in a positive direction. Forever the data collector, you decide to pull the cask down and weigh it to get a feeling for its total liquid contents. You immediately notice two things: First, the weight has dropped a bit, but nothing too consequential. Second, upon opening the bung and peering into the cask, you can tell the level has dropped a bit—you figure around 10 percent, give or take.
So, the volume has dropped a significant amount, but the weight hasn’t changed as much. Putting these things together, you figure—correctly, I might add—that the volume drop is most likely from the whiskey soaking into the wood. Make a note, shrug the shoulders, and put the cask back.
Another year goes by, and you figure it’s time to check that cask again. The color and cask character are more intense. Check the weight and volume, and you find that both have gone down a bit, this time appreciably and in sync with each other. No leaks appear to have formed around the barrel. You also notice the proof has gone up a bit—or possibly down, but that’s a discussion for another time. Regardless, you know that your distillery accountant is going to have an aneurysm. (Hmm, maybe best not to tell them anything just yet.)
The years float on, and the liquid inside the cask continues to improve. After five years, you decide that the flavor is pristine, and that your bourbon has matured to perfection. It is now time to dump the cask for bottling. Because your regulatory authorities—TTB, CRA, HMRC, your accountant—require you to measure the amount of alcohol you collect for bottling, you take measurements on the final weight. And you find that the liquid inside the cask has depleted by almost 25 percent.
For distillers, what I’ve outlined above is so mundane and commonplace that it almost seems gratuitous to describe it. Even many spirits consumers have at least a slight grasp on the phenomenon of the angel’s share. Spirit goes into the barrel, time goes by, evaporation happens… and, in the end, the distillery has less liquid to sell.
But there’s more going on than loss.
Let’s Dive a Bit Deeper
The oak used to make casks is a porous substance.
“American white oak is so incredible because it is liquid-tight and air-porous,” says Jane Bowie, founder of the Potter Jane Distillery in Springfield, Kentucky. “Esterification is a beautiful thing, and what oxygen can do to whiskey is awesome.”
The incoming oxygen is massively important for all manner of maturation reactions to occur. However, it’s a bit more complicated to wrap one’s head around the evaporating spirit and its role in maturation.
Depending on the warehouse conditions, we expect to see about 10 percent reduction in spirit volume from inside the cask in the first year. As we mentioned above, most of that liquid has soaked into the wood itself, though some of it is still evaporative. Year-on-year beyond that, you can expect to see evaporative losses of 2 to 5 percent.
Generally, in milder climates such as those in Scotland and the rest of Britain, the losses hew toward the lower end of that spectrum. In Tennessee and Kentucky, where things get a bit hotter for a good chunk of the year, the losses are on the higher end of that spectrum. More extreme climates will exhibit losses well outside that range—there are distillers in India who have seen an average of 15 percent angel’s share loss per year.
Brad Berron, research director for the James Beam Institute at the University of Kentucky, goes into more depth: “Some level of angel’s share is unavoidable in cask maturation,” he says. “Based on our measurements of spirit flow through solid oak, you’ll lose about 2 percent a year in a perfectly sealed bourbon barrel in Kentucky. Once we start considering the joints in the barrel, the angel’s share will come to roughly double that. I would consider unavoidable losses to be roughly 4 percent a year in Kentucky. If you’re way above that number around here, you have some significant leaks or a maturation environment that is promoting loss.”
Terms like “loss” and “reduction” tend to force the human mind to think in negative terms. With regard to the angel’s share, however, it’s not all bad.
Berron notes that the loss is tied to flavor development: “The most obvious connection is the concentration of flavors as some materials leave the barrel,” he says. “We also see some interesting effects as air comes into the cask to balance the spirit that is leaving. That influx of air drives oxygenation of the spirit and all of those wonderful oxygen-mediated maturation reactions. The movement of any liquid through wood is strongly related to temperature and humidity. So, you’ll see more angel’s share with high temperatures and more arid climates. (Sorry, Texas.) The bright side is that many maturation reactions are also driven by temperature, so you may get favorable profiles faster in warmer climates.
“You may notice that I completely dodged the good versus bad argument,” he adds. “The only thing we can say for sure is that the flavor would be different if you were able to change angel’s share.”
Adding Through Loss
That last point is important and nuanced. The angel’s share isn’t just one thing—it is a vaporous mirror to the liquid spirit maturing inside the cask. Because of the financial implications, we often think of the angel’s share as nothing more than a net loss of alcohol and water, but the truth is that it’s so much more than that.
Take acetaldehyde, a highly volatile compound with a boiling point of 68°F (20°C) at sea level. Despite its high volatility, acetaldehyde often finds its way into the new-make spirit. In smaller amounts, it lends a green-apple aroma to the liquid. Higher amounts can have a seriously negative impact on a spirit’s character. Fortunately, acetaldehyde easily evaporates out of the cask wood, carried along by the vaporizing ethanol and water losses.
Another set of examples includes some of the more nefarious sulfur compounds, such as hydrogen sulfide and dimethyl sulfide. Often found in brandies, rums, and whiskeys, these little molecules can really muck up an otherwise-wonderful distilled spirit. In casks with a char layer, these compounds are adsorbed onto the activated carbon. However, they also leave the cask through the angel’s share.
The cask’s ability to allow for gas exchange is important to the liquid’s development. If gases are exiting the cask in the form of angel’s share, then logically we should expect that gases can enter the cask. Oxygen is perhaps the most important component here, as it leads to a variety of maturation reactions. Some of these are very complicated.
“There is comprehensive, research-based evidence to support the role and impact of oxygen in the maturation of spirits/wines,” says Matt Burgess, business development manager for Speyside Cooperage in Craigellachie, Scotland. Oxygen’s influence includes “contributing to oxidation [and] reduction reactions, interacting with catalyzing copper ions present from distillation to produce hydrogen peroxide, [and] oxidizing ethanol to acetaldehyde to acetic acid, to then cause esterification reactions to ethyl acetate and amyl acetates.”
Burgess also adds that oxygen enters the cask at multiple points through a number of different means and that we should be cautious about ascribing too much praise for oxygen ingress until more research is done.
The Barrel’s Environment
Previously, we noted that warehouse conditions dramatically affect the angel’s share. An aspect that many folks may not have considered is that the angel’s share from whiskeys and other spirits may be changing in subtle ways as distillers alter and upgrade their warehouses.
Commercial spirits have been stored in barrels for hundreds of years, if not longer. Early distilleries were often small affairs, servicing the imbibing needs of their local communities. In those early days, casks would be stored in ways that allowed for ease of access, not necessarily for maximum space efficiency. Naturally, some distilleries fared better than their peers and gradually grew their enterprises beyond their local confines. These expansions necessitated more efficient barrel-storage systems, so they could store more casks in increasingly smaller footprints. The systems have become traditions of their own.
For instance, during the 1800s, distillers in the United Kingdom and France were widely using dunnage systems. They would stack barrels atop each other perhaps three or four units high, often in buildings with earthen floors. (Dunnage systems are still heavily used in some spirit categories today, though not so much in the majority of the Scotch whisky industry.)
There are a variety of pros and cons to the dunnage system. The first is the earthen floor. Whether dirt or gravel, these substrates tend to retain moisture, increasing the overall humidity in the warehouse. Higher humidity would favor an increase in the amount of alcohol loss to the angel’s share, thus bringing the overall alcohol concentration inside the cask down. That reduction in cask alcohol concentration, while of considerable consternation to accountants, will change the internal cask reaction and extraction profile.
Contrast that with more modern warehouse designs, and you can clearly see that over time, as warehouse construction has evolved, so too has the liquid inside, creating subtly (and sometimes vastly) different spirits than in the days of yore.
Burgess, with his long history of studying maturation in Scotch whisky, concurs. In Scotland, warehouse construction over the years has shifted away from smaller, lower-height dunnage warehouses, which “keep a cooler average temperature and don’t have much temperature stratification.” Instead, he says, it moved toward taller brick and stone warehouse with higher racks and more storage efficiency—but they “now introduce a considerable height difference between the top and bottom of the warehouse and the associated temperature stratification that comes with it.”
Today, there are more modern, steel-framed warehouses with high racks, Burgess says, and these “bring the same stratification but also introduce a much higher rate [of] internal temperature fluctuations, due to limited thermal mass of the building structure.”
Certainly, one of the primary claimed benefits of dunnage systems is that they keep temperature stratification to a minimum and produce more consistency among casks. In modern rickhouses dotting the fields of Kentucky and Tennessee, barrels can be placed on the top floors of nine-story buildings—though building codes have changed in many areas in recent years, and many new warehouses have a max height of seven stories.
Those upper-story barrels will see wildly higher temperatures and lower humidities than barrels in the lower reaches of the warehouse, impacting the quality and character of the angel’s share. That’s one reason that some whiskey fanatics make note of where certain releases were kept in the warehouse. In fact, there are entire brands that have been at least partially built around barrel location in the warehouse. Jim Beam’s Booker’s brand famously touts that the barrels are usually pulled from the “center cut” of the warehouse—midlevel—where Booker Noe liked to pull his personal bourbon.
Of course, the whiskey going into those casks is the same as in the rest of the warehouse. The truth is that the character of the angel’s share has shaken things up a bit.
Stiffing the Angels
It sounds as if the angel’s share is an integral—if fiscally annoying—part of the whiskey-making process. But what if it doesn’t have to be that way?
For as long as the angel’s share has been a recognized phenomenon, distillers have tried to figure out ways to reduce its impact on spirit volume. And many have tossed it to the wayside when it came to light that these methods somehow negatively impacted the whiskey. These failed attempts haven’t stifled progress on the matter, however.
The folks at Devil’s Cask in Somerset, Kentucky, have been working for years on evaporation-reduction technologies that don’t sacrifice character. They now believe they’ve pulled it off with what they call their SpiritLock Technology.
Devil’s Cask’s CEO Jeremy Grunewald has a unique take on the concept of the angel’s share: “We see it as an operational inefficiency that poses significant challenges for distilleries in terms of product loss and operational sustainability,” he says.
Essentially, if you can control for the flavor, then the spirit losses become a form of inefficiency. And why wouldn’t we try to correct that?
Grunewald elaborates: “Distilleries have long accepted the loss of product during maturation as an inevitable aspect of whiskey production, often attributing it to tradition with little effort to manage or mitigate these inefficiencies,” he says. “If 3 percent is lost this year and 4 percent the next, it’s simply dismissed as ‘the angels being thirsty.’
“While we respect the heritage and mystique that surround whiskey-making, we believe this hands-off approach falls short of modern standards for optimization and control. In virtually every other engineering or manufacturing sector, inefficiencies are scrutinized and refined to achieve optimal outcomes. Yet, in whiskey production, these losses remain shrouded in tradition, often treated as an untouchable part of the process.”
While some may cry foul over such efforts as an affront to Mother Nature’s tried-and-true traditionalism, I could easily see some distillers clamoring for a more modern alternative. The cold reality is that money pays the bills better than idealism, so the Devil’s Cask’s approach is a potential a game-changer for some distillers. (And their website contains a load of data to devour, if you want to learn more.)
Regardless which side of the angel’s share fence you prefer, it’s hard to deny its significance. To some distillers, it’s a natural and even desirable part of the spirit-making process. To others, it’s an unfortunate financial loss that should be avoided.
More research is needed to better understand its effects and impacts. Until then, I’ll feel little need to pour one out for the angels. It sounds like they do just fine on their own.