Barrels and Wood in Whiskey

Author -  Ben Hodgins is a final year student on the brewing and distilling course at IT Carlow. He has written the following piece on the barrels and wood for Flying Tumbler. 

Ben Hodgins

What’s the first image that comes to mind when you think of whiskey? If you’re like me it will be the picture of the tall wooden barrels, stacked high in a long dark warehouse filled to the brim with sweet golden-brown liquid we enjoy so much. Comparable to a treasure chest hidden away with the golden loot we all want to get our hands on, but there’s more to these wooden cornucopias then just storing our product. Without casks and the wood that is used we wouldn’t have whiskey. There are many different types of casks and many different types of wood that when used properly produce an array colours and flavour notes that make whiskey… well… whiskey.

There are 5 major factors of a cask that contribute to what your whiskey will end up like after the aging process:

  1. The size of the Cask.
  2. What predecessor lived in the cask before you use it.
  3. The level of charring or toasting the barrel has.
  4. Whether the cask is a first fill or a refill.
  5. The type of wood used.

When looking at the size of different casks it’s clear that they change a lot. This is because there is no defined volume of a standard casks. There are coopers all around the world that will define what they think is the best size cask for their needs, because of this discrepancy in size it can cause challenges when you want to give your whiskey a finished aging. Let’s start with what we’re familiar with; An American Standard bourbon barrel will hold 200L of spirit, a normal butt will hold 500L, a Sherry Hogshead can hold 245L, and a Cognac type cask will hold 300L.

After size we’re going to look at what type of drink was living in the cask before it reaches us and how that can affect the flavour when aging. With the interest of time, I will only be going over some of the most common types that are seen within the whiskey industry. The most frequently used cask in Irish Whiskey would have to be the ex-Bourbon barrel. From the name you can probably guess what type of liquid was hiding in here beforehand… When using this barrel to age whiskey you’ll find that it brings out a golden colour with tasting notes of vanilla, sweetness, and caramel. From here we can go up to an oloroso sherry butt. This is one of my personal favourite cask finishes. This casks previous liquid is of the sherry type and produces flavours of dark ripe fruits and deep nutty flavours while giving a lovely amber/red colour to your whiskey. The last example we’ll be looking at is a Bordeaux cask for whiskey aging. This cask type previously had red wine within and transfers flavours of strong red fruits, grapes and berries while giving a red colour to your aged spirit. At flying tumbler we use a mixture of ex-American bourbon , Oloroso sherry and a Californian wine barrel which give our whiskey a unique and flavourful blend.

The third factor that influences the outcome of your whiskey is the level of charring of the barrel. There is a major difference between the charring and toasting of a barrel. Within the wood of a barrel there is a supply of sugar. Different woods have different levels of sugar, for example, maple wood has a higher sugar content than oak. Toasting a barrel is the process by which the cask is heated and the sugars inside liquify and expand, seeping out onto the surface of the wood. These caramelised sugars is what gives the whiskey its sweet flavour and brown colour. The difference between toasting and charring is that charring is where the barrel is hit with an open flame, burning the wood for a short period of time. The charcoal created from charring acts as a natural filter removing sharp unwanted flavours creating a smoother product. It also deepens the colour of the whiskey with aging and the higher level of char your barrel has the darker your whiskey will most likely end up.

Another major influencer is whether your cask is a first fill or a refill. American bourbon is made using virgin American oak barrels. This means that nothing has already been aged in it before. Spirits will leach aromas and flavours out of the barrels over time and so you can only have a finite amount of uses of a barrel. This number is about 4 fills for whiskey. The reason why everyone doesn’t just use virgin barrels is because first of all casks are expensive. And secondly like we mentioned earlier the fact that another product was aged in the barrel can impart delicious flavours onto your whiskey adding depth, colour and character a virgin barrel cannot provide.

Lastly, we will discuss the different types of wood and their effect on the taste of the final product. The two major types of oak used for barrels are American oak and European oak, and there are some key differences between the two. American oak grows along the east of the U.S and parts of Canada and imparts a mellow, vanilla caramel flavour. This tree also grows faster and is in turn more economical for use in barrel crafting. Other examples of different woods used for barrels are Maple which due to its high sugar content gives a sweet maple flavour and is used primarily in Tennessee whiskey production.