A cooper explains: “This is how a whisky cask is made”

Malin Åberg

Binding a cask is a highly-skilled craft requiring experience and expertise. Mats and his son David are the fourth and fifth generations of their family to run Varalövs Tunnfabrik, where they create, for example, the casks used for our popular series of 30-litre casks. In this blog post, they take you behind the scenes at their cooperage and explain how whisky casks are made.

Coopers David & Mats

What’s the most enjoyable aspect of making casks?

“I like the assembly, forming and heating the most. It’s a lovely feeling to see the finished cask and know that you have created it yourself. And it is also fun when we get flames involved, so the charring is also a favourite part. When you think ‘Wow, this one turned out really well’, then it’s an especially enjoyable day at work.”

Why do casks actually have their characteristic shape? 

“The shape comes from way back in time and was chosen so that they would be easy to manoeuvre. The characteristic barrel shape makes it easier to both roll and turn them, which, for example, simplified the work back when casks were transported back and forth by horse-drawn carts.”

How do you actually form the casks?

“To put it in simple terms, you basically use heat and water and pull in the ends that are sticking out with the help of a pulley system and a wire. (Scroll down for more details about the process).

How much does an empty/filled cask weigh and how big are they?

“They weigh approximately 10 kilograms when empty and approximately 40 kilograms when filled with whisky. They are 47 cm long, and have a diameter of 33 cm at the ends and 38 cm in the middle.”

Why do you char the inside of the casks and how is that done?

(Master Blender’s comment: The casks used by Mackmyra have the second highest level of charring, with the “crocodile skin” being visible on the cask but not having 100% coverage. At high levels of charring, the cracks that form (and give rise to) the crocodile skin effect cause the whisky to permeate more easily into the oak cask – and the different levels of charring have different chemical effects that ultimately produce different flavours. High levels of charring also result in the pleasant caramelised vanilla tone that we like in the whisky.)

“We put the cask, without its ends, in our firing area and light the inside. After a little while, the cask catches fire and is allowed to burn for 20 seconds before we extinguish the fire with water. After the charring, it is left to cool for a while. The leftover oak from the manufacturing of the casks is used as fuel for the fire during charring, so in other words the same oak from which the barrels are made creates the charring on the inside.”

How long does it take to make a cask? 

“About 5 hours from start to finish.”

Why do your casks have the shape they have, is it a specific shape or a general one?

“We use a general cask form, but can always adapt it to the customer’s wishes. Some customers want the casks to be more slender, and others want them to have an oversized belly.”

What is the biggest challenge you face when making casks? 

“The biggest challenge is actually getting hold of perfect Swedish oak, with really good quality. We get help with this from our friends at Nyhamns Såg och Båtbyggeri.”

So what happens if the quality of the Swedish oak isn’t good enough, does that make it more difficult to bind the cask? What problems arise as a result?

“Any inferior wood is filtered out prior to assembly, but if it was actually used it could result in cracks occurring while bending the staves, or some time after that. Branches make the cask leaky and can also cause the material to crack.”

What machines do you use for the various parts of the process? 

“It’s an incredible mix of old craftsmanship and new technology. Some parts of the process are done in the same way as was the case 100 years ago, while others are done with the very latest technology. Our CNC cutter, which we use to shape the staves, makes it very easy to change the shape of the casks, for example. It makes it easy and smooth for us coopers to reconfigure our work for different customers and products.”

What metal is used to bind the casks? 

“We use hot-rolled steel bands.” 

Do you try, like us, to be a bit extra kind to the environment during the process?

“Yes definitely, one example is that all the wood offcuts are converted into biofuel for heating the buildings and drying the timber.”

What are the most challenging parts of the process? 

“The assembly requires a bit of extra precision, so you really have to know what you are doing with that. Ideally, you should have done that step a thousand times before. The fitting of the ends of the cask must also be very precise, so as not to risk the whisky leaking out.”

So, now a tech-nerd question: if you want to change the shape of a barrel, do you do it in a 3D software program first and then program it in the CNC router?

“We can do it in a number of ways, with the modern approach being via the CAD program to the CNC. But we can also make our own templates by hand for manual feeding through an older machine.”

Now perhaps one of the most important questions: do you have a whisky cask yourself?

“Haha, unfortunately not yet, but hopefully soon. When I place an order I will definitely choose a smoky cask.”

THE PROCESS, STEP-BY-STEP

STEP 1

It all starts with us receiving planks from our friends at Nyhamns Såg och Båtbyggeri. We cleave the timber to create staves and put these on pallets with space in-between them, so that they dry. The staves then lie there for what we in the industry call “two weather years,” which means for two summers. During this period, the weather leaches the Swedish oak with its wind and rain, in a natural process that increases the quality of the timber even further. 

STEP 2

In step two, we take the staves inside and plane them so that they become convex on one side and concave on the other side. 

STEP 3

After that, we cut the pieces to the right length. In each step, we also discard the material that is not good enough in terms of quality, which requires an especially high level of knowledge about timber. 

STEP 4

The shapes of the staves are then cut, so that they get the right dimensions and can be bound to form a cask.

STEP 5

Now the really advanced craftsmanship begins. We mount all the staves in a hoop band until they are collected together in the approximate shape of a cask. The cask is then heated so that the oak can be bent and a round shape created. 

STEP 6

While the wood is hot, we put temporary hoops around the cask.

STEP 7

Once the cask has cooled, we tighten the hoops again as much as possible. 

STEP 8

Charring: (See the reply further up)

STEP 9

Grooving: — In this step we cut a groove so that we can attach the bottom to the cask.

STEP 10

Each bottom is measured so that it fits a specific cask.

STEP 11

Once we have smoothed the outside, we switch to the permanent hoops and they are “driven” into place, as it is called, with the help of a sledgehammer and a drive ring.  

END FINISHING

In the last stage, it’s time for final finishes. This involves reviewing each cask and varnishing the ends.

That’s it, it’s done!

Read more about Varalövs Tunnor and our collaboration.

More information about Varalövs Tunnor is available on the company website.