Grain to Glass - The Cooper

Continuing our occasional series along the drink's supply chain, Ron Emler explores the role of oak, and how casks transform spirit into whisky. While ex-bourbon barrels dominate the industry, some distillers are looking closer to home …    

When it comes off the still the spirit that is to become Scotch whisky is crystal clear. The golden tones only develop during maturation, when the spirit extracts pigments and other compounds from the wood that give it colour, flavour, and aroma. The amber glow and subtle smoothness develop during the minimum three years ageing it must undergo in oak.

Even today, the alchemy by which oak casks convert rough spirit into glorious whisky is not entirely understood despite extensive research. The oak has a complex semi-permeable membrane through which gases can pass. As the whisky evolves, the many different organic chemicals interact with the spirit and with each other. Over time, some  liquid evaporates (The Angel's Share) and alcoholic strength declines.

According to the Scotch Whisky Association, there are 22 million oak casks of spirit maturing in Scotland. More than seven million belong to industry giant Diageo which holds more than four million of them at its monster warehousing complex at Blackgrange, Alloa.

While the vast majority come from the bourbon states of Kentucky and Tennesse, the use of American oak is a relatively new trend among whisky distillers. Originally casks were considered purely for transportation and as recently as the 1970s much Scotch whisky was matured in port or sherry casks in which the fortified wines had been shipped to the UK for bottling. As UK demand dwindled and producers switched to bottling in Iberia, that source of cheap wood shrivelled although some houses still use port or sherry casks to give their whiskies an extra cachet.

Under US rules all bourbon must be matured in new, charred oak barrels that may only be used once, ensuring a steady supply of empty casks.

Scotland's once extensive oak forests have been neglected and the artisan skill of coopering has declined. To reverse that is not impossible, but as Matt Burgess, Development Manager of Speyside Cooperage, explains: "On the open market today a standard American barrel costs about US$185: a Scottish cask costs about £1,200."

The economics are obvious despite the cost of shipping casks to Scotland. Not only that, Burgess says distillers get quicker extraction from American oak which can reduce the time needed for ageing and make casks available for refilling more quickly, which pleases the bean counters.

Speyside has cooperages in America where it builds about 750,000 casks a year. The likes of Diageo, Suntory and Pernod Ricard supply some of their cask requirements from their own US distilleries but most whisky distillers source either via long-term relationships or through brokers on the open market.

Until about a decade ago most bourbon casks were disassembled and flat-packed into containers for shipping. Today the vast majority are transported whole.

Iain McAlister, the master distiller at Glen Scotia in Campbeltown, brings in 200 casks a year from Jim Beam in Kentucky. He insists they are delivered intact.

"The barrels have a better moisture level and take to the spirit better; they have the original liquid layer still intact. We visually check them and potentially pressure check them at best.  Simple as that. But you have to remember it is the original wood type, how they were seasoned, how they were charred, toasted and coopered and finally the usage, these all make a big difference," he says.

At Diageo's biggest cooperage at Cambus in Alloa where up to 400,000 casks a year are treated, Mark Burt explains that each one is inspected before its first fill and subsequently when it returns for repair and treatment.

The highly automated plant employs 45 fully skilled coopers but forget any images of them manually shaving staves, hammering hoops and charring barrels over an open fire in the traditional manner. Cambus is a high-tech plant on an industrial scale by necessity to meet the group's needs. Even then some complex tasks are contracted out to other cooperages.

At Cambus, robots dismantle the casks, repair and ‘de-char, re-char' them as required under the coopers' skilled eyes, all the while ensuring each cask's original components stay together. The shaving process involves scouring an average 3mm from the inside, before re-charring. "A freshly charred cast is more active," says Burt.

Some casks outlive a human lifespan. Matt Burgess remembers an 80-year-old Glenlivet which was matured in a barrel that was not its first fill. But as he points out, the number of times a cask can be successfully repurposed depends on a blender's choice of age profile and target market.

On average, the life of a cask is reckoned to be two or three fills with Scottish malt spirit after which many are used for maturing grain whisky.

Bourbon itself is in a slump, but American oak casks remain in demand, not least for final maturing of tequila and mezcal. Port and sherry producers also want them for ageing their wines and some have set up their own coopering facilities across the Atlantic.

"There's an unspoken question in Scotland," says Burgess. "What would happen if American law changed to allow bourbon casks to be used for more than one fill? Nobody wants to answer it."

"There's a little bit of a worry about supply" admits Gregg Glass, whisky maker at Whyte & Mackay, who has intimate knowledge of oak and its effects on maturing spirit.

"European oak is more expensive than American casks and it's less efficient, you may get less yield from it," he says, "but we started thinking differently about our maturation policy and to look at responsibly sourcing Scottish oak."

In conjunction with Forestry and Land Scotland and the Fasque estate in Aberdeenshire, Whyte & Mackay is conducting a long-term experiment to test which of two oak subspecies would grow most successfully and produce the best results for whisky barrels

In 2000 they planted 13,000 saplings near their Fettercairn distillery. "Although it's a 150 to 200-year programme, in my lifetime we ought to be able to identify which thrive best in the same environment and which will prove the best", Glass says.

Not only does this herald a potential future for using more Scottish oak but it is very eco-friendly - for every tree felled in the experiment at least six will be planted.

"I can stand on the edge of the forest and see the sawmill, the farms that supply some of the barley to Fettercairn, the distillery's water source, the distillery and the warehouse in which its whisky is matured," he says proudly.

"The holistic benefit is that we are bringing cask making back to Scotland."

To achieve that Scotland will need a swelling supply of trained coopers. Whyte & Mackay is expanding its apprenticeship scheme as are Diageo and Speyside, among others.

The programmes last four years so with proper planning there should be sufficient to maintain and replace those 22m casks gently maturing around the country, whether the oak continues to come from Kentucky or the Highlands.