Cask Curriculum: The Essence of Oak

Oak. Where would we be today if it weren’t for the mighty Quercus? The world would be a bleak place, I can tell you that much. Why, you ask? Well, if it weren’t for the existence of oak, whisky would not exist! By law, Scotch whisky must be matured in an oak cask for a minimum of three years. The majority of the whiskies we enjoy today, however, are aged much longer than that, often decades. With so much time spent in wood, it comes as no surprise that a great deal of a whisky’s flavour profile can be attributed to the type of cask it’s aged in.

So what are the most common types of oak and how can you know what to look for in choosing the whisky that best suits your unique palate? Let’s have a look…

Unlike our native spirit of Bourbon, which must be aged in new American oak casks, Scotch whisky can be aged in any type of cask, new or used, so long as it is made from oak. This lack of restriction means that when it comes to producing Scotch whisky, the different styles and flavours offered by the spirit are endless. Some casks will yield a spirit that is light, floral and fruity, while others are dark, rich, and spicy. The options are plentiful when it comes to developing flavour in Scotch whisky, all thanks to the unique characteristics of each oak cask.

American Oak

There are no less than 600 species of oak but only a few are used for whisky maturation. Step into almost any warehouse in Scotland today and you may be surprised to see the majority of casks made from just one: American white oak. Undoubtedly the most plentiful (and perhaps affordable) type of oak, most of American oak casks are imported from Bourbon distillers in America. That is to say that before they were used to mature Scotch whisky, they were previously used to age Bourbon in the good ole’ USA.

Whisky aged in American oak tends to fall on the lighter side of the flavour spectrum. Vanilla, honey, citrus, and hint of coconut are just some of many notes you can expect to find in American oak-matured malt whisky. A classical representation of a Scotch whisky matured in American oak is Cask 39.167 ‘A big tropical adventure’ or, if you’re looking to turn up the wood influence to maximum, Cask 105.21 ‘Truly mesmerizing!’ demonstrates how a whisky aged for more than a quarter century can evolve into a deep and complex spirit.

European Oak

While American oak is often used to produce a lighter, fruitier style of Scotch, whisky matured in European oak is often darker, richer and far more full-bodied in comparison, making for the ideal mid-winter dram. This unique flavour profile originates from several sources; the species of wood itself, which is, by nature, more spicy and tannic than American oak, and the prior contents of the cask itself. While American oak is fully charred prior to use, European oak is lightly toasted.

When it comes to Scotch whisky maturation, the majority of European oak casks come from Spain and previously held Oloroso Sherry. The result? Dark fruit, nutmeg, clove and often a hint of eucalyptus make for an intoxicatingly rich style of whisky. For the ultimate representation of Sherry-matured whisky and a break from the frigid outdoors this winter, check out Cask No. 9.150 ‘Thyme well spent’. For something entirely unique, Cask 10.162 ‘Big wave sofa’ is an oily & coastal whisky from Islay that was matured in the lighter American oak before being finished in a dark and rich Oloroso hogshead for two years.

So is one type of wood better than the other? Of course not! Of these two types of wood, it is generally accepted that European oak influences whisky to a greater degree than American oak. Whisky enthusiasts often debate the merits of both- some arguing that European oak will often mask the flavour of the spirit beneath it. Personally, I enjoy both styles for different occasions. When I want to enjoy a lighter, more spirit driven experience on a lazy afternoon, I’ll reach for an American-oak matured whisky. When I want a rich and warming dram to carry me into the late hours of a winter’s night, European oak all the way! Finding your own preference is all part of the fun.