The art of making whisky casks is a highly skilled and traditional practice. This is called coopering. Nowadays, modern machinery aids the cooper (the name given to someone who makes casks and barrels) but it still takes several years of training to reach the required industry standards.
All are trained to use the traditional tools and methods and use them alongside more contemporary equipment. Watching a cooper at work is fascinating, but what are the stages of a whisky barrel from tree to being filled with spirit? Here is a quick explanation.
Read more about the Influence of Oak Casks and Barrels on Whisky and Whisky Cask Sizes and Types.
- The oak trees are only cut down when they have reached sufficient maturity. This is when the tree is at least 7.5 metres (25 feet) tall and one metre (3 feet) in diameter. The age of the tree will differ depending on the type of oak and where it is grown.
- The trunks are transferred to a sawmill. They are sawn into planks from which the correct length of the stave is cut. A stave is a small plank that links together to form a circular barrel. These are initially straight but will be curved later to aid barrel construction.
- Traditionally a cask is formed of 32 staves with 15 more being used to create the heads (the two ends of the barrel).
- In order to bend the staves to the correct shape, they are exposed to heat. This makes them more pliable and able to be made into the required concave shape that curves inwards.
- A cooper will plane down the staves so that they fit together tightly without leaking. This is done using natural tension without the use of nails, or any glue. The staves are held securely in place by a series of metal hoops.
- Wood is a porous material and the distillers want the whisky to interact with the air. Therefore, no varnish or paints are used on the casks to allow the wood to ‘breathe’.
- Once the outer sides of the barrel are constructed and held in place, the cask will be toasted or charred on the inside using heat and flame. Toasting gives a lighter effect and colour, while charring is darker and heavier. This is done to help with the penetration of the spirit into the wood and control the rate of maturation.
- The heads are then fitted and made watertight by forcing dried reed fibre into the small gap between the head and body of the barrel. A specialist tool is used for this.
- A hole is then drilled in the barrel to allow easy filling, checking of the whisky’s maturation and final emptying. This will be either on the body for a traditional dunnage warehouse, where the barrel lays on its side, or in the head. This will be done if the cask is destined for a racked or palletised warehouse where it will stand on its end.
