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14 October 2011
The art of woodcraft
By Richard Croasdale

Oak casks have long played a familiar and fundamental role in the creation of malt whisky – but how is our understanding of how the wood interacts with raw spirit evolving?

Anyone who claims the magic is being taken out of whisky making should walk around a warehouse with a master distiller and watch how they unconsciously touch and stroke the casks as they pass. This writer has personally witnessed a grown man hug a hogshead out of sheer, unbridled love.

Because, however large and efficient the industry becomes (as seen in our visit to the ultra-modern Roseisle last issue), there is no escaping the fact that wood – fickle, variable wood – will always be the one thing which separates the most sublime dram from the raw spirit it once was.

The basics of maturation have changed little over the centuries. Oak remains the material of choice for cooperage; it is easy to work with, effectively watertight and grows abundantly across the northern hemisphere. And, fundamentally, a cask is still a vessel that must be up to the task of containing spirit for decades if necessary.

What has changed is our appreciation of how wood interacts with the raw spirit, and the extent to which tiny variations in the cask can lead to very different characteristics in the mature whisky.

Through its innovative ‘single oak project’, US-based bourbon distiller Buffalo Trace is at the forefront of the ongoing drive to perfect this understanding – so much so that Jim Murray described their study as “breathtaking” and “historic” in the last issue of Unfiltered.
Started 20 years ago, the single oak project used 96 American white oak trees (known as Quercus alba), individually selected for their growing conditions and growth ring density. “We divided each tree into top and bottom, giving us 192 unique sections for cooperage,” explains master distiller Harlen Wheatley. “For each of the resulting barrels, we used different levels of charring and recipes of spirit, then aged the whiskey under different warehouse conditions. So, from 96 trees, we’ve ended up with a total of 1,344 taste combinations, no two of which are exactly alike.

“What makes the project interesting is that, within those 1,344 combinations, you’re still only working with seven critical variables, so you can really work out the influence of each on the end result.”

Dr Jim Swan, a renowned authority on maturation and cask management, believes Buffalo Trace produce the most desirable casks for use in Scotch malt whisky production. “They are made to a higher specification, using air-dried wood and the best build standard. And then there’s the quality of the whiskey; it’s a light, fruity type of bourbon, which goes well with most Scotch whiskies.”

The work at Buffalo Trace is reflected by similar research and innovation among Scottish distillers who increasingly see their role as starting in the forest, with the live oak. Even as secondary barrel users, some Scottish distillers have moved away from the “found wood” tradition, by directly specifying their own casks at source.

Glemorangie’s head of distilling and whisky creation, Bill Lumsden, explains: “Selecting the right wood to begin with is critically important. Our control over that process has to be absolute.”

To this end, Glenmorangie owns a forest in the Ozark Mountains in Missouri from which it can manufacture its own casks. Lumsden adds: “We have experts out there selecting individual trees and working with local cooperages to produce casks to an exact specification.”

Once manufactured, Glenmorangie’s American oak casks are sent for use and seasoning at the company’s partner distillery in Tennessee, before being shipped to the UK, ready to produce their first batch of Scotch malt whisky.

US whiskey barrels, which account for the vast majority of vessels imported for Scotch malt whisky maturation, are manufactured from American white oak and US regulations state that they can only be used once in America.

Many of the flavours we associate with ex-bourbon casks come from a thin layer of charring on the inside of the cask, created by allowing it to burn for between 25 seconds and a minute. This charring, which takes place before the spirit is put in the cask, brings about a chemical change in the surface of the wood, caramelising and breaking down key botanical compounds.

The second major source of casks is Europe, which continues to supply a smaller but vital number of casks previously used for sherry and other wines. Dealing with European casks is quite a different proposition, as the volumes imported are smaller, the variety much greater and cost is an issue too.

European oak – also referred to as English oak, French oak or Quercus robur – is found in patches around the UK and across continental Europe. It has a different internal structure to American oak, often with a coarser grain, and is associated with a spicier, more astringent flavour profile.

Just as the best American white oak comes from the specific soil and climatic conditions of the Ozark Mountains, so European oak varies considerably depending on precisely where it is grown.

In very wet climates, for example, the vessels in the wood will be bloated to accommodate extra water, creating a problematically swollen, loose grain. Too dry, and the tree will grow slowly and become very dense, again making it unsuitable. For trees to grow tall and straight – a desirable quality for cooperage – they generally need to come from a well-stocked forest, which provides both protection from the elements and competition for light.

Some of the best cooperage wood ever to have come out of Europe was once grown in Poland. Casks made from Memel oak (it shipped from the port of Memel, now Klaipeda in Lithuania) were highly water resistant, strong and reputedly lasted decades longer than other vessels. Sadly, Poland’s supply of Memel oak was utterly depleted during the First World War.

Scottish oak is generally deemed unsuitable for cooperage, while English oak does not command a much better reputation. French oak is prized by wine makers and is always the material used for Sauternes casks, while Spanish oak has traditionally been used for sherry casks.

However, in recent years, distillers have hit a major problem sourcing Spanish oak sherry casks, as many bodegas have moved to cheaper American oak.

Bill Lumsden says: “Most of the sherry casks used in the Scotch whisky industry by distillers who care about their product will be what we call ‘sherry shipping casks’, which are manufactured specifically for the Scotch whisky industry. It’s not really to transport the wines, as the name would suggest; the wine is just used for seasoning.”

The Macallan is one of the largest Scottish importers and users of sherry casks. Its parent company, the Edrington Group, also brings in casks for other Scotch distillers.

Like Glenmorangie, The Macallan has new casks coopered and seasoned to its own specifications. From felling a tree in Spain to the sherry-seasoned butt arriving in Scotland takes around six years and costs The Macallan somewhere in the region of £600. This is around ten times more expensive than an ex-bourbon American oak barrel.

George Espie, The Macallan’s master of wood, believes the extra control is worth the high price. “Commissioning our own casks gives us greater control because we’re going back to the forests for them. We’re taking them from sustainable woodland and monitoring the whole process.

“Our wood policy is one of the most robust in the industry; it covers everything from the specification of the staves – thickness, width – to the precise seasoning and levels of toasting.”

Whereas American whiskey barrels are char treated, oak wine vessels are typically toasted over an oak chip fire to achieve the chemical changes that create character.

The toasting process is graded from light to heavy, with each setting bringing out different characteristics in the wood.
Toasting is one area where Dr Jim Swan believes significant improvements could be made, if cooperages took note of new technologies being used in American wine butt construction.

“For their wine butts, they have a barrel profiling technique, where the barrel is toasted over an oak-chip fire in the normal way, but a computer program has been developed to give highly consistent results.

“That can produce very specifically flavoured barrels, but it is not yet in use in the whisky industry. There’s definitely scope for more flavour creation.”

Finally, while its use is much more restricted, Japanese oak (or Mizunara) provides an interesting coda to any discussion of whisky and wood. Originally used in the Japanese whisky industry as an experiment during the Second World War, when American and European wood were harder to come by, Japanese oak was found to be too porous and strongly flavoured for Scotch-style maturation.

Today, Japanese distilleries still prefer to follow the Scottish tradition of using American whiskey and Spanish sherry casks in the majority of cases. However, the use of Japanese oak has continued to develop and now gives Japanese distilleries flavour options not available in other countries.

Chris Bunting, author of the Nonjatta whisky blog, explains: “Mizunara barrels give a distinctive flavour to their whisky. It has been variously described as evoking sandalwood, coconut and a type of oriental incense called ‘Kara’.”

Such variety explains why distillers across the world return to the good old Quercus family. Everything we love about whisky, we owe to the still mysterious properties of the remarkable oak. And, until the sad day when science allows us to grow forests of identical, entirely predictable trees, it is the unique nature of every stave which will keep us coming back for more.

Take a closer look at oak
Staves: Staves are always taken from the heartwood of the oak; the core at the centre of the trunk which no longer carries water
and nutrients. While the cellulose flesh of the wood is porous, concentric layers of resinous cells stop liquids from penetrating all the way through.

Roots: Despite their size, oaks have a relatively small root plate. There is a theory that they can only collect the nutrients they need to thrive with help from specially adapted fungi. These fungi coat the tree’s roots and spread great distances, collecting minerals from the soil

Acorns: Beset by insects, hungry animals and hostile climate, an individual acorn’s chances of becoming a tree are a little less than one
in 10,000

Lifespan: Once developed, an oak tree can grow to up to 80 feet tall and live for several hundred years.

Tall tale: The story of an unusually large oak tree in Connecticut is regarded as a symbol of American independence. Legend has it that Connecticut’s constitutional charter was hidden in the hollow of a large oak tree in 1687 – to avoid it being confiscated by English colonists. The tree became known as ‘The Charter Oak’ and is commemorated on the Connecticut quarter coin.

The roots of oak use: When not tending to his charges at the Royal Botanic Garden Edinburgh, Alan Bennell (pictured) can often be found relaxing with a dram at the Members’ Room at The Vaults in Leith. A botanist, long-standing Society member and inveterate raconteur, Allan has two driving passions: whisky and wood. “The oak has an almost unique resonance in western culture,”
he enthuses.  “You see oaks come up again and again in the bedrock of our history, with treaties signed under them and kings hiding in them.  “And in America, oak was the settler’s salvation; the first American settlers knew oak, they understood its properties. So when they saw this American white oak, Quercus  alba, and they saw  how straight it grew, they used it to manufacture wheels, furniture and, of course, staves.” But when it comes to whisky, why did we choose exclusively to use oak and why focus on the two species Quercus alba and Quercus robur?

“One of the key characteristics of broad-leafed oak is that, between the seasons, when the new spring wood begins to grow, the tree lays down a resinous chemical blockage, known as the tyloses, which blocks up the wood and makes it much less porous.
“When it comes to our particular choice of species, it’s all about getting precisely the right characteristics.  “Quercus alba, for example, tends to be straight, reasonably slow-growing and, at maturity, they’re generally at least 25m, up to 40m. The growth rate is really key, because you want a nice dense wood. The American cooperage industry looks for around 15-17 growth rings  per inch.”
This is a topic Alan could talk about for hours – as he says: “The deeper you dig into this, the closer the story of whisky follows the story of the oak, and  of man’s relationship with it... that’s something to think about over  your dram!”

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