How the Ex-Bourbon Barrel Defined Scotch Whisky

Scotch whisky and ex-bourbon barrels have enjoyed a long-lasting and harmonious relationship. In fact, over 90% of all scotch whisky is matured in ex-bourbon casks today. Considering there are some 22 million casks sitting in Scottish warehouses, that’s a lot of casks!

But it wasn’t always this way. So how did the ex-bourbon barrel become the preferred choice for Scottish distillers? To find out, join The Single Cask as we celebrate all that’s great about ex-bourbon whisky barrels. Let’s begin by stepping back in time to understand how whisky maturation came about.

The History of Scotch Whisky and Oak Casks

Scotch whisky hasn’t always been the carefully matured spirit that we know and love today. In fact, you could say we are spoiled for choice with the variety of exotic and flamboyant-sounding cask releases that tantalise our tastebuds. However, there was a time when a whisky cask was nothing more than a container.

For a long time earthenware or animal skin containers were commonly used for the transportation of liquids, with the Roman amphora being a famous example. However, the Celts of Western Europe began manufacturing early casks made from all manner of wood types, bound together by strips of willow or hazel. The word ‘tun’ claims its origins from the Celtic word for ‘skin’ – tonda.

By around 300AD the durability and capacity of these new-fangled wooden containers had superseded the more fragile earthenware options. The qualities of oak also appeared to improve the taste of wine that was commonly stored within them. This is well before the first accounts of anything resembling scotch whisky. Many of these casks were produced in Cisalpine Gaul, an area occupied by the Celts and from where the name ‘cooper’ originates.

Leap forward a thousand years or so and oak had been the favoured choice of wood for casks containing everything from grain to oil, to wine, and even gunpowder. Spanish sherry had also become the top tipple in England. By the end of the 17^th Century, around 90% of all ‘Vino de Xerez’ exports were to England. Shipped in ‘butts’, from the latin ‘buttis’ meaning wine-skin or cask.

Naturally the sherry trade resulted in a great many empty sherry butts being distributed across Britain. They just so happened to be excellent for holding and transporting the wine of Scottland too – whisky. Sherry butts, whilst being the most widely available, were not the only casks up for grabs. Brandy, wine, port, and madeira were also traded in casks. So what changed?

The ’New Deal’ for American Whiskey

American whiskey had been bubbling away since the 17^th Century, although for a time rum distillation was the more common spirit. 1783 saw the first registered distillery producing Kentucky whiskey, shortly before the advent of liquor taxation. America, like central Europe, had abundant oak forests of straight and tall trees from which to fashion casks. It’s regarding this topic, however, that things became interesting in 1938.

Franklin Roosevelt’s “New Deal” implemented legislation that required all bourbon whiskey to be matured in new oak casks. What are commonly called virgin oak casks today. This meant that a cask could only be used once for bourbon whiskey maturation. A prosperous deal for the cooperages and lumber businesses!

Of course, bourbon is matured in a specific standard of cask called a barrel. The word barrel being also of Celtic origin – ‘baril’ and the later French ‘barrail’. These American barrels were originally 48 gallons (around 180 litres), but today the standard is 53 gallons (200 litres). Although US federal law only stipulates that whisky should be stored in ‘oak containers’ with no minimum capacity. Now where does scotch whisky fit in?

Scotland Welcomes the Ex-Bourbon Barrel

An abundance of discarded ex-bourbon barrels in America meant one thing – cheap barrels were readily available for export. So from 1944 onwards, ex-bourbon barrels began to be shipped to the UK for scotch whisky maturation alongside the still in use sherry butts. But, something crucial happened in 1981.

It was in this year that Spain introduced a new law. To protect the quality standards and geographical identity of Xerez wine, it became law that all sherry must be bottled on home soil in Spain. Hence, overnight the supply of sherry in casks ceased in the UK. So too did the availability of sherry casks for whisky maturation.

For the suppliers of ex-bourbon barrels it must have been a moment of high-fives and celebrations. This is why ex-bourbon barrels are used to mature over 90% of all scotch whisky today. The sherry casks that are popular, rather than being left-over containers, are tailor-made for the scotch whisky industry and are therefore costly.

The Flavour of an Ex-Bourbon Cask

Oak casks can be thought of like tea bags. The more you use them the less they have to give. This is why bourbon whiskies have such strong oak-derived aromas such as coconut and vanilla. It’s all due to the exclusive use of virgin oak casks. But in Scotland the style is a little different.

Although virgin oak is used for scotch whisky as an exception, Scotch whisky distilleries seek a finer balance between the spirit character and wood. Whether this is from choice or from a history of using second-hand casks is an interesting question. To soften the impact of oak further, and to increase the cask capacity, most ex-bourbon barrels will be increased in size for scotch whisky. A larger cask means less contact between the spirit and wood as a percentage ratio.

To save on shipping costs the 200 litre barrels from the US will be broken down into their individual staves (there’s no point shipping air!). Coopers in the UK will remake the barrels but using a greater number of staves per barrel and new heads. Thus the capacity of most casks will be increased to 250 litres, which you will know as a hogshead. These casks will most commonly be produced from American oak, a different species to European oak, providing a unique blend of flavour attributes for the maturing spirit.

American oak is renowned for imparting high levels of oak lactones into whisky. These are molecules responsible for those delicious vanilla and coconut aromas. The use of flames to heat the inside of the casks also plays an important role too.

Called toasting, it helps to caramelise and make available elements within the oak. These can range from toffee and creaminess from a light toasting, all the way up to chocolate and spice from a heavy toasting. In addition to toasting, the casks will also be charred. This layer of charcoal helps to remove some undesirable characters from the maturing spirit such as sulphur, along with further opening up the wood.

Single Cask Whisky and Ex-Bourbon Barrels

Today, the influence of bourbon barrels on the Scotch whisky industry is profound and far-reaching. Many Scotch whisky brands, including single malt whisky and blended scotch whisky icons, owe their distinctive flavours to the time spent in these barrels. Brands like Glenfiddich, Lagavulin, and Johnnie Walker have all utilised bourbon barrels to create expressions that have garnered international acclaim.

It's a fascinating thought that the lobbying of the coopers and lumber companies in the US shaped the characteristic style of bourbon whisky. In turn, the abundance of single use casks of American oak has influenced what has become the ‘tradition’ of scotch whisky. Helped along of course by the Spanish government in 1981.

If it were not for these events, how would scotch whisky taste today? It’s an impossible question but it creates an opportune moment to raise a large glass of single cask whisky to the humble ex-bourbon cask. The mainstay of scotch whisky and a crucial component of flavours that we know, love, and celebrate today.

Ex-bourbon barrels create wonderful characters in scotch whisky. The level of toasting, charring, and where the wood came from all add up to produce unique and unrepeatable experiences. Take a look at out latest releases to explore in our online whisky shop by clicking this link: Shop Single Cask Malt Whisky | The Single Cask