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Explained: A Guide to Whisky Casks and Sizes

by Matt Chambers
at Whisky for Everyone
12.07.23

Much of the flavour comes from the cask

The different types of whisky casks and sizes, plus what they are made from, have a profound effect on the Scotch whisky spirit maturing within.

Many people say that much of the flavour – up to 75% – comes from the cask. The natural colour has a bearing too, as new spirit coming straight from the still is transparent.

The direction and flavour profile that a Scotch whisky takes over the subsequent years depends on several factors. But what are whisky casks made from, what are the regulations and what are the different sizes available?

Which Wood Types are Used for Whisky Casks?

In Scotland, a whisky cask must legally be made from oak. The wood is very durable, robust, and watertight when made into a barrel. However, the origin of this oak can be from any location in the world. That said, two main types are used – American oak (Quercus Alba) and European oak (Quercus Robur).

American oak is widely used within the bourbon and American whiskey industry. The most common region for growing American oak is the Ozark Mountains in the state of Missouri. Whiskies matured in such casks tend to be sweet with butterscotch and toffee notes and mild warming spices. American oak is also high in a compound called vanillin, which smells and tastes like vanilla. 90% of all casks maturing in Scotland are of this type.

European oak is used to mature a variety of drinks including sherry, red wine, brandy, and numerous fortified and dessert wines across Europe. Oak is sourced from regions in France, northern Spain, Portugal, and Hungary for this. European oak casks lend rich nutty and spicy notes to a whisky, plus darker sweeter characteristics such as caramel and toffee. Just under 10% of all casks in Scotland are of this type due to expense and lower availability.

Legally, the Scotch Whisky Regulations 2009 state that a whisky cask cannot exceed 700 litres in capacity and that the spirit must mature within it for a minimum of three years. Fail on either of these, or several other criteria, and you cannot legally name your product as Scotch whisky.

Common Whisky Cask Sizes

The size and shape of a whisky cask has a direct relationship to the spirit maturing inside. The larger the barrel, the lower the wood surface to spirit ratio – this lessens interaction between the two. Therefore, a larger barrel is better for long maturation times. Conversely, the smaller a barrel has a greater surface area compared to the amount of liquid. Therefore, interaction is also much greater.

Hogshead

The hogshead is the most common cask size found in the Scotch whisky industry. The name is derived from the old English ‘hogges hede’, an ancient unit of measurement equivalent to 63 gallons. Almost always made from American oak and used in the American bourbon industry. The capacity is 225 litres.

ASB (American Standard Barrel)

The rather unromantically named ASB is a smaller version of the hogshead that was developed in America for standardisation purposes. The capacity is around 200 litres. They are made from American oak and used heavily by many bourbon and whiskey producers. These barrels are very common in Scotland.

Butt

This long, narrow cask with tapered ends and wide staves is most used by sherry producers in Spain and often made of Spanish oak. These huge casks can hold 500 litres and are the most common type of ex-sherry casks in Scotland. The large size makes them very good for long maturation, but equally as good for a sherry finish.

Puncheon

This cask type is like a butt, but with a shorter and dumpier shape. There are two types – the ‘sherry puncheon’, which is used in the sherry industry and made using narrow staves of Spanish or European oak, and the ‘machine puncheon’, which is constructed using thick staves of American oak and used to mature rum. Both have a capacity of 500 litres.

Scotch whisky barrels

Alternative Cask Types

There are many other sizes of cask available to whisky distillers and these range in size and shape from the massive to the bijou. Let us start big and work our way down.

Gorda

This huge barrel has a capacity of 700 litres and is mostly used in America. It is the largest size that is legally allowed to be used in Scotland. They are very occasionally used for maturation but are mostly used for marrying different whiskies in a single malt batch, or for doing similar for blended whisky.

Drum

This short, wide cask is also massive and carries a capacity of 650 litres. They are made using thick staves of European oak and are specifically used to mature Madeira, the fortified wine from the Portuguese island of Madeira. They are rarely seen in Scotland but have been known to be used for finishing.

Pipe

Another large cask type, this time long and narrow. They are commonly made from European oak and look like a butt that has been stretched from either end. They are the main cask used to mature Port wine and are used in the Scotch industry for finishing. Pipes have a capacity of 650 litres.

Barrique

Often used in the wine industry, a barrique is a barrel with a capacity of 250 litres. These casks are made in a different way and use wooden strips to hold the staves together, rather than metal hoops as in a traditional cask. Barriques are used mostly for finishing in Scotch. If you see ‘ex-red wine finish’ on a label, it will have been in a barrique for that time.

Quarter Cask

A quarter cask is exactly that – a cask that is one quarter the size of a regular cask. However, this is where the confusion begins. If the quarter cask is of American origin, then it will be 50 litres in capacity (i.e., one quarter of an ASB). But if it is of European origin, then it can anywhere between 80 and 125 litres (i.e., one quarter the size of a butt). Often used to accelerate maturation due to the large interior wood surface area.

Octave

The octave follows a similar idea to the quarter cask but is one eighth the size of its parent cask type. An American octave is very small at just 25 litres, while a European octave can range from 50 to 80 litres depending on its origin. Rarely used for full maturation due to the very high wood to spirit ratio but used to finish a whisky or accelerate maturation.

Blood Tub

A small cask often used by brewers. It has a capacity of just 40 litres and has an elongated oval shape that made it traditionally easy to carry on horseback. Not used often in the Scotch industry but can be seen occasionally if a whisky undergoes a beer cask finish or for experiments.

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