Nowadays we mostly know the word cooper from the surname (think Anderson, Bradley or Sheldon). But like so many surnames, the name Cooper is actually based on an old craft or profession. Imagine you’re being asked to come up with your own surname. What would you choose? What defines you? For many people in Medieval times, the obvious choice was their profession, giving us surnames such as Baker, Smith, Potter or Taylor. While some of these professions have continued to be commonplace in the modern era, others have become more arcane over time. The surname Cooper surely falls into the latter category, reflecting the fact that casks are no longer the most common way of storing things. With the notable exception of the wine and spirit trade of course…

Let’s take one step back. So what exactly is a cooper? Wikipedia tells us that a cooper is someone who makes wooden, staved vessels, bound together with hoops and possessing flat ends or heads. Google puts it more plainly, explaining that a cooper is a maker or repairer of casks and barrels. But while Bradley is undoubtedly talented on the silver screen (and Sheldon Cooper’s Fun with Flags is always a barrel of laughs), no one still expects them to be skilled with staves and hoops. And indeed coopering is a bit of a dying profession, yet the craft remains vitally important for the whisky industry. Luckily there are others who have now taken up the trade.

Of course, for a whisky, a cask is something far more than just a vessel in which to spend some time while being transported from A to B. Yet the fact is that maturation was just a happy by-product of the need for storing whisky somewhere after distillation. Being watertight, easy to stack, roll and place upright, oak barrels were the perfect option for storing the Water of Life. At some point it was noticed that the casks not only changed the colour of the spirit, but also impacted its flavour in ways that took the rough edges off the whisky. And although the exact science of maturation continues to be somewhat of a mystery, the positive effects are undeniable. Distillation determines a whisky’s general character, but it’s the maturation in oak that develops the spirit into something more sophisticated and expressive, bringing huge variation to a spirit that was once identical when it came off the still. Much like a person’s upbringing determines how they develop certain character traits as they mature, so the wood nurtures the raw spirit into an end product. Policy makers have taken note: we’ve now come to the stage where legally speaking, without resting under oak for three years, Scotch whisky isn’t even whisky, but just raw spirit. And rightfully so: there are some distillers who claim that up to two-thirds of a whisky’s flavour profile is determined by the maturation process. While this of course depends on the age of a whisky, it’s undoubtedly true that casks, and by extension the art of coopering, remain one of the most important aspects in creating a quality whisky.

There was a time when each distillery would have its own cooperage, with a cooper’s tasks consisting mainly of making new barrels from scratch. Nowadays though, advances in transportation allow distilleries to import casks from anywhere in the world. To save up on space, casks are usually taken apart and then reassembled once they reach their destination. This is made easy by the fact that casks are made up of individual wood staves, which are held together without the help of glue or nails. Instead, the staves are arranged exactly right and bound by iron hoops. In the presence of liquid, the wood expands, creating a waterproof seal. it The slightest misalignment means the cask would seep, rendering it useless. This is craftsmanship at its most precise, beyond anything a production line could manufacture. Before use, coopers burn the cask on the inside, to open up the wood and allow its natural sugars to caramelise. This can be anything from a light toast to a heavy char, depending on the flavours sought after by the distiller.

So why do distilleries prefer used barrels over new casks? Is it just simple Scottish stinginess to buy something second hand? Not quite. The fact is that wood should shape a whisky’s development, not dominate it. New wood – virgin oak as it’s known – is still so packed full of flavours that it would easily overwhelm any whisky you place inside it. For maturing whisky, it’s therefore much better to use a cask that has already been worn in a little bit. Luckily, Scottish distilleries have managed to form a symbiotic relationship with the bourbon makers of North America. By law, bourbon should be aged in new Quercus Alba – unused American white oak barrels, which of course need to find a new home after their first use. Each year, about a million such barrels become available, half of which end up in Scotland. Scotch makers call these first fill barrels when they hold whisky for the first time, and refill barrels when they’ve already held whisky once before. These casks will be much more subtle than virgin oak, but still provide enough of those tasty vanilla flavours that distillers are after. In total, a cask can be used for up to six times, not bad for a piece of wood that costs roughly $50 to acquire!

The other main wood used for maturing whisky is European oak that previously held sherry. Although sherry is now somewhat out of fashion, there was once a time when the drink was hugely popular with the British masses. It was imported from Spain in large 500 litre sherry butts, which were impractical to be shipped back to their country of origin. Scottish distillers leapt at the chance to snap up some cheap casks, and found that ex-sherry wood has a very positive effect on the taste of the whisky, imbuing it with sweet and rich nutty flavours. With sherry being less alcoholic than bourbon, it permeates less deep into the oak, meaning there is simply more wood left to enjoy in an ex-sherry cask. For this reason, coopers char bourbon barrels before re-use, but only give sherry casks a light toast, so as not to destroy the flavour. Even so, sherry casks too can overwhelm a whisky, which is why many distillers opt for a partial maturation in both ex-bourbon barrels and ex-sherry butts.

Another possibility is to finish a whisky in casks that previously held another type of liquid, to give it a unique flavour profile. Especially in recent years, a lot of experimentation has taken place, with distillers using casks that previously held port, rum, wine, cognac, ale, smoky whisky, or a combination of these. Even virgin oak is used on occasion. Again, distillers need to take care not to dominate a whisky’s flavours, so for finishing, anything between a few months and a few years of extra maturation suffices.

Lastly, a cooper should know what type of vessel they’re handling. You will have noticed a wide variety of terms being used in this post. A point of confusion is that the term barrel is often used as a catch-all phrase, but is actually just one type of cask. There are many other variations, so here’s a short overview:

Barrel: This almost always refers to the American Standard Barrel being used in the bourbon industry. It has a capacity of 200 litres and is made of American white oak. Most Scotch is aged in casks that were barrels in a previous lifetime. However, before being used in the Scotch industry, barrels are usually repurposed into hogsheads.

Hogshead: At 225-250 litres, a hogshead is slightly larger than a barrel. To account for the difference in size, a cooper will take the staves of 5 broken down barrels and reassemble them into four hogsheads. The advantage of doing this is that it allows for more efficient use of warehouse space; not unimportant when you’ve got thousands of casks stored at any one time. Although it’s hard to prove definitively, many distillers also believe that the larger cask size improves the quality of the whisky somehow. Either way, the vast majority of all Scotch is aged in hogsheads.

Sherry Butt: As the name indicates, butts are used to age sherry. With sherry being a product of Spain, it makes sense that these casks are made of European (Quercus Robur), rather than American oak. They are much larger in size than barrels, with a capacity of 500 litres. After hogsheads, butts are the most widely used type of cask in the Scotch whisky industry.

Quarter Cask: Ahhh the Quarter Cask. Increasingly popular in recent years, this cask is – unsurprisingly – a quarter of the size of a barrel, at a capacity of 50 litres. This results in a much smaller surface to spirit ratio, which speeds up the ageing process significantly. Quarter casks are mostly used for finishing a whisky, to give it those extra vanilla and caramel flavours.

Port Pipe: Aptly named, port pipes are long and narrow in shape and are used to hold port wine. Now popular for finishing Scotch, these casks have a capacity of a whopping 650 litres.

Barrique: Popular in France, these casks are commonly used to store wine or cognac. With wine-finishes becoming increasingly trendy, these casks can now also be commonly found in Scotland. They have a capacity of either 225 or 300 litres, depending on which region of France they originate from.

Since each cask is essentially a product of nature, no one cask is exactly the same. For this reason, whisky aged in ‘identical’ casks can actually turn out quite differently after a few years of maturation. For this reason, distillers will often marry different casks together to smooth out the differences and ensure the consistency of the products that end up on the shelves. An exception to this are single cask bottlings. These whiskies truly are unique: once all bottles of a certain release are consumed, the world will never see its exact like again (although subsequent bottlings may come close).

Enough about casks though, back to coopers. As mentioned previously, coopering is a bit of dying profession. So where might you still see this art on display? Most distilleries no longer have cooperages on-site, so you it’s not something you’re likely to come across during a distillery tour. To achieve lower costs and economies of scale, most coopering activities are now outsourced to specialised companies that are not open to the public. There is one notable exception though: the Speyside Cooperage in Craigellachie. The Speyside is littered with distilleries, all of which make use of the coopering skills of the Speyside Cooperage. The Cooperage has a visitor centre, which offers guided tours for as little as £3,50. As advertised, the tour will take you from ‘acorn to cask’, explaining all the steps needed to prepare the oak for maturing that precious Water of Life. During the tour, you will see the coopers live in action. It’s really fascinating to watch, and you can’t help but be impressed with the sheer craftsmanship that goes into this work. And if that doesn’t convince you of the skill required to manufacture a cask, you can try it for yourself. The Cooperage provides miniature samples of staves. All you need to do is put them together and fit a hoop around them. Sounds easy enough, right? Think again, I soon grew both frustrated and even more admiring of the coopers in the room just below.

Coopering is such an important, yet often overlooked part of producing a whisky. While many of us have been on a distillery tour where we are almost reverently shown the warehouses in which the whisky is slowly maturing, we hardly ever spare a thought for those artisans that have helped to craft these wooden time capsules. It is quite amazing to think that every drop of whisky we get to taste has passed through a collection of hand-me-down wooden vessels, that have slowly imparted their flavour to the spirit. Without the time-honoured skills of coopers, our whisky would taste nowhere near as good. Let’s raise a toast therefore to the men and women who continue to uphold the traditional art of coopering, those crafty carpenters without whom whisky would never be more than just spirit.