The types of whisky casks and their flavours

The humble oak cask plays a pivotal role in the character of all scotch whisky, whether it’s single malt whisky, single grain whisky, or blended whisky. What was once nothing more than a container in the guise of a wood barrel has become a defining period in a whisky’s journey. Whisky casks today are available in a wide variety of shapes, sizes and types, from bourbon barrels to sherry butts. Understanding how they each influence flavour can therefore be exciting and bewildering in equal measure.

At The Single Cask we are champions of the individuality of each cask. But we are also champions for making the best whisky accessible and easy to understand. To illustrate the nuances of the different types of whisky casks, in this guide we shall cover everything you need to know. From the different whisky cask sizes to wood types, and previous fillings. By the end you will be an expert on how casks and barrels influence a whisky’s personality. Let’s start with the basics – the different types of oak for whisky maturation.

What type of oak is used for whisky?

Throughout the northern hemisphere there are around 600 different species of oak. However, when it comes to making whisky casks, the oak must have particular qualities. The wood grain needs to be porous enough to allow the spirit to penetrate the wood, but also tight enough to prevent excessive leaking. The oak must contribute characters and flavours to the whisky that are favourable and balanced. Plus the oak trees must grow straight and true to produce good quality and strong whisky cask staves.

To meet these needs, two species of oak dominate the scotch whisky industry. American Oak (Quercus alba) is the most used wood for Scotch whisky casks, with European Oak (Quercus robur and Quercus patraea) being the second most common. A third species of oak, Japanese oak (Quercus mongolica), is famous for Japanese whiskies and is only seldomly employed for maturing scotch.

The species of oak has implications for the character of whisky matured in the casks. American Oak is rich in compounds called lactones which in aged whisky are associated with creamy characters such as vanilla, coconut, and butter. European Oak has a looser grain which means the maturing spirit can seep deep into the cask staves with greater ease and leach out flavour compounds. European oak is therefore associated with higher tannins and wood spices, being also lower in lactones than American oak.

How cask size affects scotch whisky’s flavour

Scotch whisky is matured in oak casks of a great many different shapes and sizes. At the smallest end of the scale are the rarely used Blood Tubs (30 – 40 litres), Octaves (50 litres), and Quarter casks (120 litres). At the other end of the scale the largest casks are Puncheons (500 – 700 litres). The most used whisky casks, however, are Barrels (190 – 200 litres), Hogsheads (225 – 250 litres), and butts (475 – 500 litres). But how does the size of the cask influence a whisky’s character?

The ability of a cask to influence a whisky’s maturation is largely dependent on the ratio of spirit to oak. A small cask will have a higher proportion of the spirit in direct contact with the oak. Whereas a large cask will have a lower proportion of the spirit in direct contact with the oak. This enables spirit in small casks to extract colour and character from the oak at an accelerated rate. This is why younger whiskies matured in small casks can be full of character and colour. However, larger casks such as Butts can be better suited to longer maturation periods where the whisky will also benefit from non-oak related changes such as oxidation.

Discover bourbon casks, sherry casks, port casks and more

New oak whisky casks, often called virgin oak casks, impart wood characters to the whisky very rapidly. Hence, they are used with caution for maturing scotch whisky because the whisky can become too oaky within a short time. Oak casks that have previously been used or seasoned with another liquid are therefore favoured as some of the harshness of the oak will have been softened.

With so many other alcoholic drinks being matured in oak, there are many different options available for maturing scotch whisky. Casks that previously matured bourbon whiskey are the most common choice, and you can learn all about why in our article: How the ex-bourbon barrel defined scotch whisky. Sherry casks have also become extremely popular, followed by port casks, madeira casks, rum casks, and a plethora of wine casks.

An important point to know is that while many casks such as bourbon casks and wine casks are the biproduct of wine or spirit maturation, the popularity of casks such as sherry casks has given rise to a different approach. Sherry is traditionally matured in a ‘solera’ of casks that are so well used that they impart virtually no woody flavours to the sherry wine. Such casks would be useless for maturing whisky. Casks are therefore being made and seasoned with young sherry solely for the purpose of maturing scotch whisky. The sherry within them will become too oaky and undrinkable, often being destined for vinegar production.

Regardless of the cask’s previous fill, each one will have its own personality and will create a whisky that will never be repeated. It’s important, therefore, to approach each single cask whisky with an open mind and a sense of adventure. Understanding the previous fill of a whisky cask will provide some broad indications of the types of characters you should expect, so here is what you need to know.

Bourbon Casks are most often crafted from American oak. Therefore, such casks are renowned for their vanilla and coconut characters. Some casks are more active than others which means the intensity of the oak can be noticeably variable. Standard bourbon barrels have a 200 litre capacity, but they are often broken apart in Scotland and remade into 250 litre Hogsheads.

Sherry Casks can be either American or European oak with a capacity of around 480 litres. Oloroso sherry casks are the most common for whisky maturation, which are often associated with bold flavours of nuts, dried fruits, and spices. Pedro Ximénez sherry casks are also often used which is a darker, sweeter, and richer style of sherry.

Wine Casks come in a wide range of sizes and shapes in both American and European oak. As such their characters are wide-ranging and diverse, depending on if the wine was red, white, or sweet. Wine casks tend to contribute to curious characters in whisky that are less common, such as cherries, herbs, and unsurprisingly, grapes too.

Rum Casks are most often 200 litre American oak barrels. The molasses base for the rum can often come through as a deep and rich note in the whisky, accompanied by fruitcake and spices.

Port Casks are sometimes called port pipes or puncheons and are some of the largest casks made from either American or European oak. Port cask matured whisky is renowned for its rich fruit characters and sweetness and are often favoured by distilleries who produce a heavy spirit.

Madeira Casks can also offer a rich variety of characters ranging from orange zest and soft fruits to nuts. Madeira cask sizes vary but are normally around 220 – 250 litres.

How do you pick a good scotch whisky?

From what we have covered today we can draw some broad guides that will help when picking a good scotch whisky. Firstly, whiskies from an American oak cask will often display more coconut and vanilla characters, in contrast to European oak cask matured whiskies which may be more spicy and woody. Secondly, casks smaller than 200 litres will often express more vibrant woody notes at a younger age, whereas larger casks can be favoured for older whiskies. Thirdly, the previous fill of the cask will play a significant role and will be worth paying attention to.

Because single cask whisky is so varied and diverse, such whiskies can often break the rules. This is why we categorise all of our whiskies by mood rather than cask type. It’s designed to help you to get a feel for a whisky’s overall personality regardless of how it has been matured. It’s also why we have selected an expert team of Taste Masters to assess our casks before they are bottled. This way you can feel assured that only casks of whisky that meet our stringent standards will be bottled and made available.

With this in mind the best way to understand different whisky cask types is to explore a wide range of whiskies for yourself. Use this guide as a starting point to help navigate the many options. Use our Flavour Moods to discover the styles of whisky that best suit your taste. And trust our Taste Masters tasting notes to dive deeper into each whisky’s personality. Above all, discover the depth, diversity, and charisma that single cask whiskies have to offer. Head over to The Single Cask shop to browse a few just now.