American vs. European oak – what does it mean for whisky?

We're getting into the differences between American oak and European oak, and what it means for the flavour of your whisky. 

If you’ve been around here for a while (or even just for the last month!), you’ll have heard us mention different types of oak time and time again. Generally, the distinction will be between either American oak or European oak. 

We decided to delve into the differences between these because of this month’s Kavalan Concertmaster, produced at Taiwan’s King Car Distillery, which matures its whiskies exclusively in American oak – never European. 

This is because of the country’s high humidity and warmer temperatures, which sees the top floor of the maturation warehouse soaring to 45°C! Higher temperatures mean an increased interaction between the cask and the spirit, so the gentler American oak is favoured in this instance. 

But we’re here to get into the nitty gritty of it. Why do certain oak types impart the flavours that they do? It’s about to get technical… 

Laying the groundwork

First, a quick recap. Scotch whisky can only be matured in oak (for at least three years before it’s legally called whisky), while the rules for bourbon are even more strict, as it has to be aged solely in new American oak. 

Other countries can be a little more experimental – whiskies from countries like Ireland and Canada can use other woods. The famed Midleton distillery in County Cork has even used chestnut casks. 

In short, oak is pretty important. People will try to quantify how much of a whisky’s flavour is down to the wood type, and how much is from other factors. But that’s an impossible task. 

Before we start, it’s worth noting that although it’s referred to as European oak, you can generally assume it’ll have come from either France or Spain. Most commonly, European oak will be Quercus patrea or Quercus robur, while American oak is known as Quercus alba.

It’s all down to molecules

It’s all very simple really. You have three main molecules: eugenol, vanillin, and something called the ‘whisky lactone’. American oak has higher proportions of vanillin and the ‘whisky lactone’. 

The ‘whisky lactone’ is actually called beta-methyl-gamma-octalactone (you can see why it’s got a nickname), which is responsible for coconut flavours. We’re awarding no prizes for guessing which flavours vanillin imparts. Yes, it’s vanilla. 

Finally, eugenol adds drier, spicy notes – flavours like clove –  and is found more commonly in European oak. Generally, this is found to be slightly more tannic and astringent, which is why hotter countries are less likely to use it – though that doesn’t mean it isn’t delicious with the right whisky, in the right climate, as so many distilleries have demonstrated! So that’s the basis of what makes these oak types so different.

Grain – but not the kind you distil… 

The varieties of oak also grow differently – how this is then reflected in the wood itself is referred to as grain, and the grain of a wood refers to the size of the annual growth circles. 

Fast-growing wood results in a coarse grain, compared to slow-growing wood which shows a tight, fine grain. European oak usually presents a larger, coarser grain, while American oak presents a finer grain. 

Why does this matter? The size of the grain impacts how various aromas are released from the wood – as the grain size increases, meaning it’s more tightly-knit, there is a decrease in the concentration of these aromas, because a tight-knit grain allows less spirit to evaporate. 

So that’s the basics of a rather complicated topic. Remember, this is before you char or season the wood. The whisky world is filled with possibilities, and oak type is just the beginning! 

Jess 🥃