Oak barrels are an essential part of Whisky making. They house the liquid during the maturation process but they also lend some of their woody flavour to the overall taste.
Oak is
perfect for
Whisky barrels, as it is sturdy yet porous. It will hold the liquid without leaking but is also permeable enough to allow the Whisky to
absorb its flavours.
Types of Oak used in Whisky production
There are several
different types of Oak and each one
imparts a different flavour. The three main ones used in ageing Whisky are:
-
Quercus Robur (European Oak),
-
Quercus Alba (American Oak) and
-
Quercus Mongolica (Japanese Oak).
The two most popular types of European Oak are
Spanish and
French. French Oak creates a fruity flavour that is often very desirable in Whisky.
Sherry casks, rather than being made from Spanish Oak, are more likely to be made from
American Oak as this allows less liquid to be lost to the
Angel’s share. In a hot climate like Spain it is economical to choose a denser wood.
Sherry Casks also give a wonderful
spiciness to the Whisky, with cinnamon and cloves really coming through. Think
The Macallan,
The Glenrothes,
Glengoyne or
Benromach.
Bourbon Casks
Bourbon is matured in good old
American Oak. Today around
90% of Scottish and Irish distilleries also use American Oak casks. Bourbon barrels tend to be slightly charred to give a
smoky boost. The wood intensifies the flavour of the char and makes it
sweeter.
By law, Bourbon barrels cannot be reused to mature Bourbon itself but they are very commonly reused for
maturing Whisky.
Charred American Oak gives a great
smoky yet sweet flavour. Flavours like vanilla, honey and caramel, along with nuttiness and some spice, are the tell-tale signs of an American Oak cask. Think
Irish Whiskey, Kilchoman, Laphroaig, Ardbeg 10 Year Old or
Girvan single grain
.
Japanese Oak
And that just leaves Japanese Oak or
Mizunara, which is of course mostly used for
Japanese Whiskies. In the 1930s Japanese Oak became the most popular wood for maturing Japanese Whisky, but unfortunately, it is very
soft and porous, making it more likely to leak. As such, like most of the rest of the Whisky world,
Japan turned to Sherry and Bourbon casks to mature their liquid.
They still use the Japanese Oak casks for
finishing their Whisky, giving it honeyed, floral flavours with a slight hint of wooded spice as well. Check out
Bowmore's Mizunara Cask Finished Whisky from 2015 to see how it differs from a classic Bowmore Whisky -- delightful!

So yes, the Oak is vital to get right if you want to make a great dram.