There simply wouldn’t be Scotch whisky without whisky casks. These oak barrels play an essential role in whisky’s transformation from barley in the field to amber liquid in the glass. Not only do casks help protect the whisky from outside elements and contaminants, but they are also central in developing whisky’s character, flavour, colour and aroma.

In this blog, we’ll explore the three main types of casks used in the Scotch whisky industry, we’ll ask how casks are made and why they have to be made of oak, and we’ll explore how you can buy your own private whisky cask and become a member of the Borders Distillery’s 1837 club.

Why use a cask?

It’s a legal requirement in the Scotch whisky industry. The law states that in order for a whisky to be called Scotch whisky, the new make spirit must be aged in an oak cask for a minimum of three years and one day.

For centuries casks have been used to transport alcohol, and Scotch whisky is no exception, but the requirement to age Scotch whisky in oak barrels didn’t become law until 1915 with the introduction of the Immature Spirits Act.

Why oak?

Oak is used in cask making because it’s a strong, fast-growing, readily available wood grown all around the northern hemisphere and gives whisky its unique colour and flavour.

There are two main types of wood used in Scotch whisky making. These are:

American oak

American oak grows abundantly, mainly in the eastern United States. It’s used for cask-making because it’s durable and has a tight grain.

European oak

European oak grows across northern Europe, especially France and Spain. It’s used for cask-making because it has a fine grain which allows for a slow oxygen exchange.

Why don’t casks leak?

Whisky casks swell when in contact with liquid on the inside, forming a tight seal. Skilled coopers ensure staves fit precisely, while the metal hoops act as a support.

How are casks made?

The art of making casks is an ancient one and today the method has hardly changed. Casks are made in the following way:

1. The dried logs are cut into staves (the wooden sections) and the ends are tapered and bevelled and then planed, giving them a concave profile.
2. The cooper assembles the staves inside a temporary metal hoop.
3. The new barrel is then soaked in water and heated until it takes the final shape.
4. Finally, it’s tested for watertight properties, using hot water at high pressure.

If the casks are being made to mature sherry, the inside is lightly toasted; if they’re being made to age bourbon, then they are charred inside to various degrees.

How many bottles do you get from a cask?

An American Standard Barrel contains about 200 litres which equates to roughly 276 bottles of whisky.However, this number could slightly vary due to ‘Angels’ Share’.

Angels’ Share

Angels’ Share is a term used in the industry to explain evaporation of the spirit from the cask over time. During maturation the cask will ‘breathe’ with the movement of gases, and alcohol will be lost to the atmosphere. Rates of loss vary but generally 1-2% of spirit is lost for every year of maturation.

Types of casks

American Standard Barrel (ASB)

Size: 180-200 litres.

About 95% of casks used in Scotch whisky production are American Standard Barrels (ASBs) that have previously held bourbon. By law, bourbon barrels must be made from new, charred American oak and used only once, making them ideal for use by the Scotch whisky industry.

These barrels impart golden tones and flavours of vanilla, toffee, and caramel.

Hogshead

Size: 225-250 litres.

The Hogshead is the second most commonly used cask in Scotch whisky production. These casks are made from ASBs or Butts that have been dismantled into staves and shipped to cooperages in Scotland.

There, the staves are reassembled with new oak ends to form Hogsheads, which are longer and narrower than standard ASBs. The increased capacity of the Hogshead allows for greater interaction between the whisky and the wood, making it ideal for long-term maturation.

Butt

Size: 475-520 litres.

Butts, typically crafted from American or European oak, are made in cooperages in northern Spain. They are then sent to Jerez in southern Spain for seasoning with sherry varieties such as Oloroso, Fino, and Pedro Ximénez (PX) in a process that usually takes up to two years.

These casks are very expensive, costing over ten times more than an American Standard Barrel. Whisky matured in ex-Sherry Butts acquires a reddish amber colour and notes of nutty fruitcake, berry, and spice.

How many times can casks be used?

The working life of a cask can be 50-60 years, being filled as many as five to six times during that period.

The first time that Scotch whisky is put into a used cask, the cask is known as First Fill. When the cask is eventually re-used, it’s called a Refill cask.

Eventually a cask will get to the end of its useful life. At that time, it will usually be broken down and cut into ‘whisky oak chips’ for use by the food services industry for smoking meat and cheese etc.