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A question of casks


We all know how important wood is to the ultimate character of the whisky we drink, and from a historical perspective, there has been a major shift in the types and treatments of wood used for whisky maturation, with a significant effect on the overall profile of our drams.

Traditionally, the Scotch whisky industry relied on reusing casks that had previously held fortified wines such as sherry, port and madeira, principally because there were lots of them available and they were inexpensive to acquire.

Such fortified wines enjoyed great popularity in Britain during the 18th and 19th centuries, and were shipped to the UK in oak casks, being bottled at ports such as Glasgow, Edinburgh and Bristol.

Whisky distillers soon discovered that as well as being useful containers, the fortified wine casks did something rather remarkable to the spirit filled into them, making it more mellow and giving it the illusion of having greater age than was often the case.

So it was that the Scotch whisky industry, which expanded and flourished during the later years of the 19th century, relied heavily on such casks, and in particular those that had contained sherry. American oak was the principal species used for the construction of such ‘transport’ casks.

The demand for Scotch during the 1890s overtook the supply of transport casks, so a number of distillers established cooperages to raise casks and season them with sherry. The leading exponent of this was William Phaup Lowrie in Glasgow, who also used European oak, imported from the port of Memel on the Baltic.


The use of former sherry casks and their influence on the liquid maturing in them helped define the prevailing style of Scotch whisky being consumed. European oak – or Quercus robur – is relatively porous and slow-growing, and imparts spicy dried fruits, pepper and even savoury flavours to the spirit ageing in casks constructed from it.

As time passed, the British palate began to fall out of love with sherry, reducing the number of casks available to the Scotch whisky industry. However, a handy solution presented itself in the wake of the 1935 US Federal Alcohol Administration Act, which ruled that ‘straight’ bourbon and rye had to be matured in brand new casks, although cheaper ‘American whiskey’ could be matured in refill casks.

This was largely due to the powerful influence of the coopers’ unions and the lumber industry in the US, but there was also a historical precedent. Early bourbon distillers often shipped their whiskey from Kentucky along the Mississippi River in American white oak casks, prior to subsequent bottling.

European oak: Quercus robur Refill casks at Speyside Cooperage

As shipping costs were relatively high, and Kentucky had abundant sources of oak, it made no financial sense to return casks to distilleries, so a tradition developed of bourbon being aged in new barrels. Apart from anything else, time spent in casks had a positive effect on the spirit character.

Unlike European oak, American oak – Quercus alba – is relatively dense, leading to less interaction between wood and spirit in the cask than in the case of European oak. The charring of new casks is first recorded back in 1826, and the process opens up the wood for bourbon to extract flavour, and catalyses chemical changes. Broadly speaking, the result is the development of sweet vanilla and coconut notes in the spirit.

The Gonzalez Byass sherry cask bodega in Jerez, Spain

When it comes to subsequent fills of Scotch whisky, the legendary Charles MacLean points out that “Importantly, it’s the wood (American/European oak) which bestows flavour, not the first incumbent (sherry/bourbon), except in the first-fill – and it is debatable whether traces of bourbon may be detected even in first-fill casks – the typical vanilla/coconut characters come from the wood.”

MacLean recalls a conversation he had many years go with an old employee at the Speyside Cooperage in Craigellachie, who confirmed that the first ex-bourbon barrels they handled arrived in 1946. The post-war Scotch whisky boom required large numbers of ex-bourbon casks, just as the previous Victorian boom period had required many sherry casks, and, similarly, they were readily available and comparatively cheap.

Above : Speyside Cooperage


The use of casks that had previously held sherry decreased even further after the Spanish government banned the bulk shipment of sherry in 1981. Today, distillers who want such casks order them from Spain, specifying how long they want them seasoned for, or in some cases make the casks themselves.

Of course, changes in maturation methods are just one of many variables that affect spirit character. Alterations to whisky-making practices that have been embraced by the Scotch whisky industry during the post-war decades have frequently been adopted for purposes of increased efficiency and maximisation of output.

Examples include new yeast types, faster mashing techniques, shorter fermentation times, quicker distillation, broader cut points and the use of steam heating of stills rather than direct firing. All of which make comparisons between ‘then’ and ‘now’ bottles of the same expressions of whisky so fascinating and rewarding.


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