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

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.

Benromach Whisky Distillery - PHOTO: FLICKR/ Ungry Young Man

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.

ex-bourbon casks waiting to be filled - PHOTO: FLICKR/ Paul Joseph

By law, Bourbon barrels cannot be reused to mature Bourbon itself but they are very commonly reused for maturing Whisky.

Ardbeg 10 Year Old Flavour SpiralCharred 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!

Yamazaki Warehouse - PHOTO: FLICKR/ Mikael Leppä
So yes, the Oak is vital to get right if you want to make a great dram.