Saturday 16th May is World Whisky Day – and of course, we’ll be supporting the cause by indulging in a few drams ourselves. Perhaps you will be too – and when pursuing your chosen bottle of amber spirit, then you might come across a reference to oak ageing. But what exactly does oak have to do with the production of whisky?

Well, when the spirit is matured in a cask, it picks up many of the flavours and characteristics of the wood, which add depth and complexity. Nowadays, by law, these casks must be constructed of oak. This is for a variety of reasons – it is tough and yet easy to work with, has a tight grain that prevents leakage, allows oxygen through due to its porous properties, and it is malleable without the risk of splitting fibres.

So what is it in oak that is so sought after? This would be the vanillins found in wood – natural oils that are drawn out of the cask by the whisky and add to the complexity of flavour. The type of oak used is a major factor in differences in taste, and there are three main types used. These are American Oak, Japanese Oak, and European Oak.

As expected European oak has been traditionally used in Scotland and Ireland for nearly two centuries. Originally, English oak would have been used, but these species were slower to grow than the Russian oak that was imported and had straight trunks and speedy growth spurts. Then in the mid nineteenth century the importing of sherry from Spain began, and the casks used to transport and mature this fortified wine was made from Spanish oak. Because it was cheaper, with similar properties to Russian oak, it became highly sought after, and still is, along with French oak.

So what flavours can you expect from European casks? These would generally be tastes of dried fruits like sultanas and raisins, spices, cinnamon, nutmeg, caramel, orange and Christmas cake.

So what about the American Oak? This has only been used since the end of WW2, when a law was created that stipulated all American whiskey had to be matured in new casks, therefore boosting the industry of coopering (creating the casks) that massively declined during Prohibition. Nowadays, it’s not only bourbon that uses these American casks – some Scottish and Irish distilleries use it too. American oak have fast growing trees with straight trunks, high levels of vanillins, and the barrels are deemed the ideal size for whisky to mature at the optimum rate. Now nearly 90% of the world’s whisky is matured in American oak bourbon casks.

Flavours to look out for when drinking American oak matured whisky are vanilla, honey, coconut, almond, hazelnut, butterscotch and ginger.

So that simply leaves us with Japanese Oak. This has been used in the Japanese whisky industry since the 1930s, and is also know as Mizunara oak. This wood has high levels of vanillin’s, which give a unique flavour. But the down side is that the casks were prone to leaking since the wood is very soft. Now most Japanese whisky is matured in either bourbon or sherry casks and is then later transferred to mizunara casks to gain its distinctive characteristics.

Whisky matured in Japanese Oak has hints of honey, blossoms, vanilla, pears, nutmeg, cloves and apples.

So there you are – a little history of oak and whisky, with some useful tasting notes. It seems only right now you should go and have a little experiment – cheers and bottom’s up!