Tasting Whiskey

by Lew Bryson

  American bourbon makers were among the first to use charred barrels for storing and aging their whiskey. No one’s quite sure exactly when they started charring the barrels; we’ll get more into that in chapter 6. But the difference it made was immense, and it would have an effect on whiskey making around the world.

  Charring does several things to the wood. First, it creates a layer of charcoal on the inside of the staves. Charcoal has well-known properties as a filtering agent; when wood is converted to charcoal, it gains a huge amount of effective surface area to adhere to and to contain chemical compounds. A mere gram of charcoal has about 200 square meters of effective surface area, an astounding figure. The char on the inside of a whiskey barrel grabs and sequesters unwanted aromatics, like sulfur.

  The heat of charring also changes the oak beneath the char. The sugars in the wood are caramelized in what’s called the “red layer,” a thin but noticeably colored layer in the wood that can be seen in a disassembled barrel’s staves. The alcohol in the whiskey, a natural solvent, permeates the red layer as summer’s heat expands it and pushes it into the wood. The caramelized sugars dissolve and become part of the whiskey, adding to both the flavor and the color.

  Charring also begins the breakdown of the oak’s lignin. Lignin is a natural polymer in the wood, a big and complex molecule that adds strength to the wood. As alcohol continues the breakdown of lignin that the charring began, it creates flavor compounds that will give the whiskey familiar characteristics, such as vanillin, the source of bourbon’s creamy vanilla notes, and wood aldehyde compounds, which become aromatic esters. Three of the major esters formed are ethyl syringate (which gives an aroma of tobacco and fig), ethyl ferulate (a spicy cinnamon aroma), and ethyl vanillate (a smoky, burnt aroma), all producing aromas familiar to the bourbon drinker. Another group of compounds, lactones, can give a coconut note. As the alcohol continues to break down other parts of the wood, it releases melanoidins, which deepen the flavors and add more color.

  In general, charring is so beneficial and crucial to whiskey maturation that used casks are sometimes recharred for further use. We’ll talk more about reuse later.

  Live flames and bent oak: charring a barrel

  Leaks and Leak Hunters

  Much of the smell of a whiskey warehouse comes from the slow “breathing” of the barrels. But some of it comes more directly, from leaking barrels. The coopers make them as tight as they can, and each barrel goes through a pressure test before leaving the cooperage: it is filled with water and compressed air and tightly stopped to see if any water forces its way out. Any leaks are repaired; substantial ones involve taking down the barrel and replacing or reshaping individual staves, while smaller ones can be plugged with “spiles” (small wooden spikes) or bits of dried rushes for linear leaks.

  Still, leaks may develop. As summer heats the warehouse and the whiskey expands, it will force its way through any small crevice and ooze down the barrel. As it dries, the sugars from the oak are left behind as a sticky brown stain, the source of much of that rich, sweet warehouse reek.

  Distillers have generally come to accept this amount of loss as part of the price of aging whiskey. A few distillers, though, still keep leak hunters on staff. They will prowl the warehouses, crawling over the ricks with flashlights, checking for barrels with significant amounts of whiskey drooling down the sides. When they find one, they’ll repair it in place if they can, or roll it out if they have to do a bigger job, hoping that it’s not too far back in the line of barrels that have to be removed to get at it.

  Breathing

  The uncharred part of the oak has an equally significant effect on the whiskey’s maturation, and it’s because oak does a great job holding liquids, but it isn’t perfect. Whiskey barrels are built to close enough tolerances that they can hold liquid for months or years without leaking — much — but the cellular structure of oak is such that a slow exchange of liquid and oxygen takes place over the long weeks, months, and years in the warehouse. You can smell it happening. Whiskey warehouses have a rich, almost overpowering smell that hits you as soon as you walk through the door, like richly sweet, musty caramel; overripe fruit; and damp wood, with, of course, a boozy hint of alcohol (only a hint in some warehouses, that is — I’ve been in some where I would have been scared to light a match).

  Distillers and warehouse workers grow so used to the smell that they don’t really notice it. “The only time I smell it is when there’s something wrong and it smells different,” Wild Turkey’s long-time master distiller Jimmy Russell told me, which is astounding; the smell of Wild Turkey’s warehouses in high summer isn’t so much an aroma as it is like walking into a huge, soft caramel and vanilla pudding.

  Some of that smell comes from the small leaks that develop in the barrels over the years, from the drips and drops that are spilled over years of sampling — official and unofficial — and from the wood of the barrels and the wooden frameworks that hold them in place. But largely that smell comes from the “breathing” of the barrels, the slow exchange of air and liquid that steals away whiskey at a rate of up to 5 percent a year (even more in craft distilleries that are using small barrels or aging in a particularly hot or dry climate), what distillers call the “angel’s share.”

  On the whole, Scotch whisky loses more alcohol than water in this breathing process, and older barrels have to be watched carefully, lest they fall below 80 proof and become no longer legally whisky. On the higher, hotter floors of American warehouses, more water is lost to evaporation than is alcohol, and the proof will rise, meaning whiskey could go in at 120 proof and come out, say, 7 years later at around 135 proof, stronger but reduced in volume.

  Loss to evaporation is one of the unavoidable costs of making whiskey, as certain and unyielding as taxes. It will be less in cooler climates or wet conditions, but it happens every year, without fail. Along with the growth of undesirably harsh and drying wood character as a whiskey ages past its prime, evaporation is the true endpoint of aging a whiskey. Eventually the angels can claim so much of the whiskey that the barrel dries out and leaks copiously, or even collapses when touched.

  At the same time, barrel breathing is one of the basic elements of whiskey maturation. Without this exchange, the whiskey simply will not mature properly. Why? Let’s go back to the cellular structure of oak. In the living tree there are slow-moving exchanges in the wood, through a maze of fibers and channels, for the transport of water, air, sugar, and minerals. As the oak develops more woody outer layers, the living wood — that part that is wet with sap when you saw through a tree — will develop tyloses, blockages that close off the channels. The tyloses serve to cut losses of living tissue during drought or infection. For the cooper, tyloses are what make oak a favored wood for waterproof (and whiskeyproof) barrels. They block the channels and will not pass liquid. They will, however, pass air as the liquid ever so slowly seeps out through interstitial spaces.

  Over successive summers, whiskey moves out of the barrel and air moves in. The whiskey moving out has an effect we already know about: we lose whiskey, and all we get for it is a pleasant smell in the warehouse! But as the air moves in, it contributes to all of the chemical reactions that are going on in the barrel, from the charcoal filtering arising from the char to the breakdown of lignin and subsequent development of various flavor compounds. As compounds in the whiskey mix with the incoming oxygen and are oxidized, fruity esters arise, giving whiskey those signature aromatics that simply can’t be explained by mere grain and wood. All these amazing aromas and flavors are coming from the wooden barrel . . . and all the whiskey makers were looking for was something to hold whiskey on the way to market.

  Size Matters

  Craft distillers have stirred up controversy by using barrels that are smaller than the industry standard. (In America that’s a 53-gallon barrel.) They wanted to age their whiskey in wood, but they needed it faster, because they had bills to pay. They looked at the effects of relative proportions of sur
face area of wood exposed to whiskey and decided that smaller barrels would age the whiskey more quickly. Quite a few small distillers made the decision to age their whiskey in 30-gallon, 15-gallon, 5-gallon, and even 2-gallon barrels.

  Does it work? The whiskey picks up color very quickly from the proportionately large surface area, but the flavor is different compared to “large barrel” whiskey aged to a similar color. Evaporation losses are steep, and the barrels cost more per gallon of whiskey aged, but it is a trade-off with speed of return on investment. The question is whether the whiskey is actually aging faster or aging differently.

  Scott Spolverino, a whiskey chemist who’s looked specifically at the aging process in these smaller barrels, describes the difference as aged versus matured. “Aging is what you put on the bottle: how old is it?” he says. “It has more to do with wood compounds, wood-based flavors, more extraction, and literally the time it’s in there. Maturation is the culmination of chemical reactions and evaporation.”

  Evaporation is important, but Spolverino also describes a process that takes place over time, unaffected by the barrel size. This is “ethanol clustering,” a structural coming together of ethanol and water in a way that makes the ethanol sensation on the palate smoother. “A small barrel can’t force the hand here,” he says.

  How do small-barrel whiskeys taste? I was wary of the idea at first. Even with only 20 years of drinking whiskey behind me, I’ve already encountered folks who thought they could speed this up and have been disappointed. But I’ve had some young whiskey aged in small barrels that I liked — the Ranger Creek .36 Texas bourbon, for one — and I’ve decided that maybe small barrels aren’t necessarily the horror that I’d originally thought they were.

  I’ve noticed that some small distillers are moving to large barrels as their sales and production increase, though. Larger barrels mean less evaporation — even balanced against a longer time to maturity — which means more whiskey to sell, and that’s a powerful argument. But some distillers will, I think, continue to use small barrels for at least part of their stock. The flavors are robust, and with regular sampling to stop aging when it’s peaked, that can make an appealing whiskey.

  Time Is Money

  At the same time there’s a lot more to barrel aging than simply airing up the spirit. The late Lincoln Henderson, a long-time Brown-Forman distiller who oversaw the production of such iconic whiskeys as Jack Daniel’s, Old Forester, and Woodford Reserve, told me about some experiments his team ran at Brown-Forman over 30 years ago.

  They assigned chemical engineers to study the aging process, to better understand it and to see if there was a way to shorten or improve it. Shortening the aging process is a constant attraction for whiskey makers (and their accountants); time truly is money in this business, stemming from the evaporation losses, increased taxes, and the physical needs of warehousing.

  “We made bourbon in 5 days,” he said, with a grin that was still a bit sour with the memory. “You need that air to get in the barrel, so we were feeding oxygen into the whiskey, running it over wood. It looked beautiful! But it tasted like crap.”

  What is the aging magic? Is it the speed of the exchange? Is it the atmospheric pressure, the pressure in the barrel? Is it something going on inside the wood that changes things? All good questions, and all part of the reason that we don’t make whiskey in 5 days.

  New Whiskey in Old Barrels

  Scottish, Canadian, and Irish whiskey makers use very few new barrels, and those few they do use are a relatively recent innovation. They’ve aged their whiskey in used casks for a long time, and they’ve become very good at using them to get a variety of different flavors. Bourbon casks are the most common type they use, if only because there are so many.

  There’s an element of necessity to it. American whiskey makers buy the barrels newly made and charred, and, for the most part, they use them once. American regulations require that bourbon, rye, wheat, malt (American-made; there are separate regulations for Scotch whisky), and rye malt whiskeys must be aged in new charred oak barrels. Whiskey that is aged wholly or partly in used barrels — done to get less of the strong flavors the new barrels impart — must be labeled as “whiskey distilled from bourbon (rye, wheat, malt, or rye malt) mash,” but currently the only major brand so aged is Early Times, though there are some craft whiskeys that are aged in used barrels.

  Since American straight whiskey makers can use a barrel only once, they’ve become a source of barrels for most of the rest of the world’s whiskey makers. “We’ve got the flavor out of them, now you can have them” is the joke from the Americans. “We’ll use them now that you’ve soaked the harshness out” is the response.

  It’s all in good fun, but there’s truth to it. Scotch whisky makers don’t want the strong vanilla notes that a new barrel brings, and that first use extracts most of it, which is what the bourbon makers want.

  That’s also part of the reason you’ll see much older age statements on Scotch whiskies than on bourbons. I’ve had Scotch whiskies that were older than I am, but the oldest American whiskey I’ve seen was the 27-year-old Parker’s Heritage Collection bourbon from Heaven Hill that came out in 2008. It was a beauty, a majestic whiskey that tasted much younger than it was, but that’s extremely rare. I’ve had 18-year-old bourbons that were overoaked, tannic, and astringent. There’s much more flavor potential in a new barrel, and once it’s been knocked down even by a 4-year exposure to high-proof spirit, it has a slower cumulative effect on new spirit.

  Sherry casks are the other major source of used wood for aging whisky. Usually the sherry barrels are made with European oak, which has more tannin and a different structure from that of American oak. The sherry barrels will retain some of the character of the fortified wine that was in them, and that varies with the type of sherry: dry fino, nutty/vanilla oloroso, rich, sweet Pedro Ximénez. Bourbon wood can give the vanilla and coconut aromas bourbon drinkers are familiar with. Combine the flavors of these “first fill” barrels in their first reuse with the distillery character, and you can develop delicious whiskey.

  But it’s not just bourbon casks and sherry casks, or even the occasional port, Madeira, or new oak cask, being reused. Some distillers are using second- and third-fill casks to get less wood character and more of the individual taste of the spirit and the evaporative effects. The results of these different casks can then be blended together in new ways to give interestingly varied single malt bottlings from the same distillery. In other words, don’t assume that a GlenWhatsit 18-year-old single malt is the same whisky as the GlenWhatsit 12-year-old, just six years older. It may be another prospect altogether.

  Cask vs. Barrel

  You’ll mostly see me using the word barrel, but sometimes I’ll say cask. What’s the difference? Well, barrel is mostly an American usage, while it’s usually the Scots who say cask. (The Irish mostly say barrel as well, but then, they spell whiskey the right way, too.) Nevertheless, there’s a significant difference between a bourbon barrel that’s in an American warehouse and a bourbon cask that’s in a Scottish warehouse . . . sometimes the Scottish one’s bigger.

  Bourbon barrels are sold to Scottish distillers, but they’re not shipped to Scotland as barrels. They’re knocked down into parcels of staves and hoops to save space on shipping. When they get to Scotland and go to a cooperage (often the Speyside Cooperage in Craigellachie) for reassembling, they may be put back together at the American standard of 200 liters (almost exactly 53 gallons), but they may instead be put together with more staves as a traditional hogshead size, at 225 liters (63 gallons).

  That’s one reason I call them casks — they’re not the same barrels as they started out — but the other reason is cordiality: that’s what the Scots call them.

  Warehousing

  Scotch and other distillers can play mix and match with reused casks to create different flavors in their whiskies. Bourbon distillers may take a different tack; Four Roses, for example, makes and blends 10
different bourbons (more on that here), and Beam has two different mashbills, one with a higher proportion of rye. But the usual way of getting varied flavor profiles within a distillery’s portfolio is warehouse selection.

  There are a variety of types of warehouses; that’s true in America, Scotland, Ireland, Canada, and Japan. The bizarre half-tube concrete warehouse at Kilbeggan in Ireland comes to mind; it looks like the inside of a whale in there. The craft distillers rarely have anything normal in the way of warehouses at this point in their development; Ranger Creek ages its small-barrel whiskeys in metal shipping containers that bake in the hot Texas sun. Warehouses can be on hills, by rivers or the ocean, in wooded glades, in wide-open fields, or on city streets; they can be made of wood, brick, or stone; they can be short or toweringly tall; and it can all affect the aging whiskey inside.

  Oak barrels in Woodford Reserve’s stone-walled warehouse in Versailles, Kentucky

  This is where the American distiller gets the most chance for variety in its bottlings. Think about it: the barrels are all new, charred oak, usually from the same supplier. The char can be varied slightly, and there is a trend toward toasting the heads rather than charring them, but barrels are usually done the same for all of a distillery’s whiskeys. The mashbill varies among distilleries, but again, within a distiller’s confines, there are usually no more than two at most for making bourbon. Yeast, with the glaring exception of Four Roses, is usually one strain per distiller, and the column stills are virtually identical in their output.