The Art of Wood

The Art of Wood

From a big operation to a one man band, we bring the art of the cooper into focus

Production | 07 Jun 2013 | Issue 112 | By Ian Wisniewski

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When you stop to think about it there are lots of things that are iconic about the whisky industry: from the pagodas and often breathtaking locations, to the bottlings and the stills.

But there is one item that without which whisky would simply not be whisky, the cask.

Of course to be called Scotch whisky, the spirit must have been matured in oak casks in Scotland for a minimum of three years. However there are more than just legal reasons for using oak.

While there is a certain amount of magic bestowed on the work of the stills in forming the spirit, it is the complex interaction between wood, spirit and time that gives whisky it's colour and most of its character.

It is oak's complex chemistry that makes it the ideal vessel for maturation.

Its make up includes cellulose, hemicellulose (which helps bring sweetness and colour to the spirit), lignin (which helps produce vanilla like notes and increases complexity) and tannins (which give astringency, fragrance and also delicacy).

Add a certain water tightness to this mix and you have something that moves beyond a mere container.

Oak also helps, through oxidation by allowing air into the cask. This helps to remove undesirable flavours and harshness, increasing the flavour and complexity of the final whisky.

However you have to open the wood up to get at all this good stuff, and this is where the art of the cooper comes in.

Once the cask is made, its inner surface is then either toasted (effectively gently burning the surface of the oak for a specified length of time, like toasting bread) or charred (which ranges from a light burning to a deep penetrating burn, that looks like alligator skin). This allows the spirit to penetrate and interact with the wood.

With the importance of decent wood being foremost in a distiller's mind, this edition we decided to look at two distinctly different coopering operations, from the small scale to the large production facility.

The craft cooper

What is that crackling you hear on stepping out of your car at 6:30 one misty summer morning?

It is not electricity arcing on the solar panels that have taken over nearby farmers' fields. Neither is it tempers sizzling as locals seethe at the impending arrival of power-generating windmills. No, further investigation soon reveals the simple snap-cracklepop of searing white oak from behind Pete Bradford's Carriage House Cooperage. This is where Bradford toasts and chars the wine and whisky barrels he makes from locally cut and cured wood, in the heart of Ontario's verdant Prince Edward County.

Dew still lingers on the corn stubble, and the sky is clear and blue. Already you can feel that this day is going to be a scorcher. "I do this first thing in the morning," Bradford tells me, as he feeds thin, white oak kindling into the already roaring wood fire in his single-barrel charring kiln. "By 9:00 it's just too hot out." On the ground nearby stand two recently assembled Bourbon barrels, waiting to be toasted.

Bradford is not the last of a dying breed. He's a modern reincarnation of a once abundant species that almost met extinction decades ago. He operates a one-person cooperage, although his wife, Marla, helps out, making this more of a family business. Bradford is a barrel-chested barrel maker, and clearly used to hard physical work.

In his down time, his welcoming manner and loquacious tongue makes it easy to imagine him playing the role of that jolly old fellow in red and white come Christmas.

The kiln itself is reminiscent of a heavy cast iron stove with a hole for a single large cover in the middle.

Bradford is waiting for the surface of the kiln to turn just the right colour. All of a sudden, he wraps his arms around the first barrel and hoists it on. "Hear that snapping?" he asks a couple of minutes later, "she's just about ready to ignite.

This one is a medium char, I'll leave it burn for 12 seconds." Suddenly a whoosh of flames shoot out the top and Bradford begins to count - to 13!

Then, with his burly bare arms he hurls the barrel to the ground and soaks it torrentially with a hose. Speed, it seems, is of the essence. Acrid wood smoke and sour steam fill the air.

He watches me take a couple of steps backward and smiles. Bradford knows what I'm thinking. "There's a chemical in the oak," he explains, "if you don't lay the barrel down right away it makes the whisky taste funny. It'll be sweet as cherries when it's cool." Later that evening, new barrelheads in place, he has me nose the newly charred cask. He is right. The fragrance of oak caramels is overwhelmed by waves of luscious red fruit. "You're the first person to smell that barrel," he tells me. Earlier, he had bunged it lightly to let the interior bouquet develop.

Bradford's production target is exactly one barrel per working day. I tell him it's an honour to have the first sniff.

Prince Edward County is ideal farmland surrounded on two sides by Lake Ontario, which extends the growing season. Recently, grain, cattle, and fruit farms have begun to give way to grape vines. Each year, new wineries seem to appear here. Newcomers produce the eco-friendly local wines demanded by wealthy Torontonian locavores who make "The County" their weekend home.

"They drive here in gas-guzzling SUVs then want organic tomatoes," a local tells me at a church market. That's exactly what she's selling - organic tomatoes. "They clean their ears with artisanal Q-tips," she adds disdainfully, in case I might be one of them.

Local politics aside, Bradford's cooperage thrives by supplying the county's ever-increasing number of artisanal vintners and lone distiller with local barrels. His enthusiasm for his unique craft is unmistakable. It's genuine artisanship and each individual barrel is a separate project. "They're expensive," he tells me proudly. "At $800 a pop people only use them for the very best wines and spirits." Tradition says that whisky barrels must be made from oak. Why? Because oak is uniquely watertight. "Oak is best for production distillers and winemakers," explains Bradford. "Other woods bleed. But if you've just got a few special barrels and you can watch them, then other woods give you all kinds of new flavours. Using alternative woods or blends of different woods within the same barrel produces some of the most flavourful and innovative ageing vessels," he tells me.

In addition to Canadian white oak, Bradford also crafts barrels from cherry, beech, ash and hickory.

Driving home the next morning, it's hard not to be struck by the deliberate quaint beauty of Prince Edward County.

Brightly painted old tractors sit airborne on just-as-brightly painted metal poles.

Others nestle half hidden among blooming shrubs on the manicured lawns of stone-fronted palatial new homes. These ancient Massey- Fergusons, John Deeres, and International Harvesters have been bypassed by the dull-blue Volvo farm machines that now ply the County's gentrified but still-productive fields.

Times they are a-changin' yet again in Prince Edward County. One of these changes, and a welcome one, is the rebirth of Canadian craft coopering, a trade that proliferated centuries ago when settlers and prospectors arrived here and began clearing the County's ancient hardwood forests to make way for fields of grain.

Types of oak

There are four main ones: Quercus Alba or American white oak which gives characteristic aromas of vanilla, coconut, sweet spice. All casks used by the Bourbon industry are made of this type. Some sherry casks are also produced from Q.alba.

Quercus Robur or Spanish/European oak.

The most common type of "sherry cask", this oak is higher in tannin - giving a mouthdrying effect - as well as having aromas of dried fruit, clove and resin.

Quercus Petraea or Sessile oak or French oak is used primarily by the Cognac industry but some is now being used in the Scotch and Japanese whisky industries. In flavour terms it sits in between Q.alba and Q.robur with high tannins and also a lot of spiciness.

Quercus Mongolica or Japanese oak/mizunara. Rare and expensive this species is now growing in popularity as it gives an intensely fragrant aroma of incense, sandalwood as well as pineapple and coconut.

Size of cask

Most commonly used:

Bourbon barrels [aka ASBs/Yankees]

These are made of Q.alba and contain 200l of liquid. By law the Bourbon industry may only use new, heavily-charred oak barrels. Once used in America they are sold to Scotch, Japanese, Irish and Canadian whisky distillers as well as rum and tequila producers.


This type of cask contains 225l and is most commonly made from Q.alba. They are made by breaking down a Bourbon barrel, adding some more staves (thereby increasing its capacity) and new heads (ends). Most of the whisky matured in Scotland and Ireland is aged in this size of cask.


500l in size, these are otherwise known as Sherry casks. They are most commonly made from Q.robur and have been seasoned with Sherry prior to being shipped to whisky distillers. Some will be made from Q.alba. These days, all new Sherry butts are made to order for the whisky industry.


These are the same size as butts but are shorter and fatter in shape. They can be made from either Q.robur or Q.alba.

Other types of cask

Madeira drum / port pipe

Larger in size than butts at 650l these are mostly used for secondary maturation (aka finishing) though some distillers are now experimenting with long-term maturation. Madeira drums are traditionally made from Q.petraea while Port pipes are mostly from Q.robur.


Otherwise known as a wine cask, these will vary in size between 225l and 300l and can be made from either Q,alba or Q.petraea.


The largest legal size of maturing cask, at 700l, Gordas (the name means 'fat one') were shipping casks used for transporting Sherry to Scotland and Ireland and were made from Q.robur. They are rarely seen or used these days.

Quarter casks / blood tubs

The smallest size of casks at 50l and 40l respectively, these are specially coopered mostly from Q.alba. Quarter casks are used commercially by Beam Global for short-term finishing purposes at Laphroaig and Ardmore. These are sometimes called "firkins". In the past, quarters and blood tubs would have been used for private customers of distilleries.

The proprietary cooper

As the SUV pulls into the Independent Stave Company, my nose picks up familiar notes. Vanilla, toasted marshmallow and caramel scents drift in the air, reminding of my Old Kentucky Home, where whiskey soaks into new charred oak barrels to receive Bourbon's russet-gold colour and 50 per cent of its flavour. Unlike the putrid sulfuric odours of paper mills, this stave mill and cooperage smells a lot like heaven.

But, this is not Kentucky. I'm standing in the middle of Lebanon, Missouri, perhaps the most important whiskey city in the world. ISC does not make whiskey or broker Scotch. "We just make barrels," says Brad Boswell, the president and fourth generation Boswell to run ISC.

Founded in 1912, family-owned ISC makes whiskey barrels for Maker's Mark, Four Roses, Heaven Hill, Jim Beam, Buffalo Trace and just about every other Bourbon brand. Well, there is one exception: Brown-Forman owns its own cooperage, so ISC is not making barrels for Old Forester, Woodford Reserve or Jack Daniel's.

With 1,000 employees, six stave mills and five cooperages throughout the world, ISC is a spectacle of pristine efficiency with dozens of its own patented and patent-pending machines that cut, bend, toast, char and etch wood for wine, Bourbon, rum, tequila and other beverage alcohol clients around the world. ISC is the world's largest whiskey barrel cooperage and arguably the most important wine cooperage, producing hundreds of thousands of barrels a year of all oaks and sizes.

It all starts in Lebanon, Missouri, a facility that feels half lumber yard, half industrial complex.

Once white oak trees in the American Midwest, Central France or the Vosges forests, freshly cut staves stacked outside naturally leach out some of those unwanted flavours before they are toasted or charred.

After air-drying for two years, some staves have turned black with fungus growing on the boards. "Those are for wine barrels," Boswell says. "If you think about, wine is a lower alcohol, so we have to break down the staves a little more than we do with whiskey." Some Bourbon makers may want their staves air seasoned for nine months; others a year. "But nobody wants cheap as possible barrels anymore," he says.

"Everybody wants the highest quality." Boswell and his coopering team have instrumentally worked quietly behind the scenes to help Maker's Mark create Maker's 46, which was named after the "46th" ISC profile in the experimental stage, and Buffalo Trace's Single Oak Project.

ISC has also helped with the experiments that never became public, including Hungarian, French or Romanian oak barrels. In case you're wondering if it's legal to store Bourbon in charred Romanian oak, it is. Federal regulations simply state Bourbon must be stored in charred new oak containers without specifying a species.

However, these unique trees often remind distillers why American white oak is preferred. "We've made barrels out of every wood you can think of," Boswell says. "But, white oak is really the best. It's water tight and tastes better. Many other species put out a resin flavour. Who wants a whiskey that tastes of pine tar?" The ISC facility is so spotless one could eat a peanut butter and jelly sandwich off the floor that's cleaner than most American restaurants. "We tell our employees to always have the place mother-in-law ready," Boswell says.

ISC workers bar code wood, so stacks are not mixed with other clients. One could scan a piece of wood at any time during the process and know everything about the profile.

Workers use hot water and heat to bend staves, because a cold one will snap like a toothpick when bent. With the assistance of proprietary machines, veteran hands bend the wood into barrels. For the barrel heads, a hydraulic machine pushes several grooved boards into a square that could withstand thousands of pounds of pressure. The square is cut into circular barrel head using another ISC proprietary machine.

Boswell says much of this industrial coopering could be automated, but five per cent of the staves contain defects. "Five per cent of bad wood for whiskey barrels could mean a lot of bad barrels," he says.

Once assembled, the 53 gallon barrel moves to the toasting area, where a "wood chef" scans the bar code and the barrel's profile appears on an ISC proprietary computer touchscreen that tells the worker exactly how long to toast the barrel. If the barrel gets too hot, a rubber hose releases a few drops of water to cool it down. For the barrel I toasted, the optimal toasting temperature ranged between 363 and 390 degrees Fahrenheit.

Not all clients want toasted barrels before the char. Some go straight to the char, Boswell says. Before the barrel enters company's proprietary circular charring mechanism, a worker scans barcode to determine its profile and inputs the prescribed charring length. The average is a 55 second char known as Char No. 4.

Every single step of the ISC barrelmaking process can be tracked and monitored in real time. Employees can even observe how well their colleagues are performing. Outside of employee work stations, computers with real-time graphs show how much wood or how many barrels a worker is moving per hour. The more they move, the more they get paid.

From the staves to the charring, ISC offers more than 180 variables to help clients differentiate their barrels. "We are like a corporate kitchen," Boswell says. "Not everybody wants their steaks cooked the same, and not everybody wants their barrels the same." How can a distiller trust a company who also works for its competition?

If anything, the more Bourbon distillers ISC works with the better, says Jim Rutledge, master distiller for Four Roses Distillery. Rutledge says ISC treats all distillers like family and is a major reason why all Bourbon distillers get along.

"ISC provides opportunities for their customers to spend time together via their top notch concerts they provide every other year at the Kentucky Bourbon Festival and a Day at the Races every year at Churchill Downs," Rutledge says. "Distillers and others in the production part of our business are friendly competitors and we appreciate the time together that ISC provides." Of course, it's not all just fun and games. A few years ago, ISC noticed issues with dowel-pin heads. They leaked more and were just fussy to fix.

Rutledge says ISC congregated all the distillers and came to the conclusion tongue-and-groove head-based barrels were better. Since then, all ISC barrels feature tongue-and-groove heads, which have more surface area than the two jointed dowel-pin heads.

"Because of their expertise in the barrel production process - beginning to end - ISC is the best of the best in the business and as far as I'm concerned we'll never look elsewhere for barrels," Rutledge says.

A new lease of life

The Scotch whisky industry is progressively greener, with greater efficiency resulting in less energy being used during production, while casks can also be rejuvenated rather than retired.

The practice of rejuvenating casks began in the late 1980s-early 1990s, and has been growing ever since.

It's far better than the traditional destination for retired casks, which were garden centres, where they were sold as plant containers.

But let's first consider a cask's lifecycle prior to rejuvenation. Casks can generally be used up to three or four times, and each time a cask is filled with spirit it is given the relevant reference, first fill, second fill, and so on. Each fill sees the cask deliver a progressively milder influence on the maturing spirit, with the vanilla notes of a Bourbon barrel for example correspondingly milder in a second fill than a first fill.

This is because the level of flavour compounds available for the spirit to extract from the oak cask gradually diminishes and eventually becomes depleted, leaving the cask 'exhausted' and unsuitable for aging.

However, the length of time it takes for a cask to become exhausted varies significantly. Oak is a natural product and therefore variable, which means casks show significant differences in their aging potential. A cask could provide up to four fills, totaling around 50 years service, while a worst case scenario is having to retire a cask after just one fill (which is rare).

Consequently, there's only one way to assess what stage a cask is at, and each time it's disgorged (emptied) the character of the whisky it contains is assessed. How the cask has influenced the whisky indicates whether it is still active enough to be filled again.

If the cask is deemed exhausted then a subsequent decision is whether it shows sufficient potential to be rejuvenated, or whether it's time to remove it from the inventory. Casks suitable for rejuvenation are sent to a cooperage, for a process known as dechar rechar. Decharring means removing the existing surface layer from the interior of the cask.

Sherry casks have a toasted layer to remove, having originally been toasted on a scale specified as light, medium or heavy, by heating the cask using a fire, though avoiding contact between the flame and the wood. Toasting a Sherry cask for the first time affects a surface layer of around two mms, with another two mms of underlying oak also affected by the heat (total stave thickness being around 30mms).

Bourbon barrels have a charred layer to remove, having originally been charred to varying degrees, a number one char being the lightest and a number four the heaviest. Barrels are charred using a gas burner that briefly ignites the interior of the barrel before being extinguished. Charring a Bourbon barrel for the first time affects the first two to four mms, depending on how heavy the char, with an underlying two to three mms also affected by heat (total stave thickness being around 27 mms).

One method of decharring a cask is using a large wire brush fitted to a motor, that goes up and down the length of a rotating cask. Alternatively, a wire flail can be used, which means stainless steel ropes comprising three or four strands that rotate along the length of the cask.

A more recent method, used in the past five years, is 'shaving' the interior, using a large head fitted with cutters at the end of a mechanised arm that moves along the cask.

Decharring generally means revealing a 'singed' surface, ie. going to the edge of the original char or toasted layer. Then it's a case of replicating the toasted interior of a Sherry cask, or the charred interior of a Bourbon barrel, using the heat from a gas burner. Recharred casks can subsequently be 'seasoned,' by filling them with Sherry for example, replicating the cask's original treatment in Spain.

The key question is to what extent casks can be rejuvenated ? A consensus is that rejuvenated Bourbon barrels, for example, can contribute the classic notes of vanilla and sweetness, at an intensity between a first fill and a second fill.

Rejuvenated casks may hold two further fillings, after which there is the option of additional rejuvenation, though two treatments is usually the limit.
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