Oak Species Exploration Q&A with Co-founder, Alasdair Day

1. How do different oak species impact the flavour and characteristics of whisky?

Each species of oak imparts different flavours during the course of maturation. As a botanist I am fascinated by how different oak species create these different flavours in our Isle of Raasay Hebridean single malt and comparing the spirit side by side from casks made from these different oak species.

2. Can you explain the role of oak in the maturation process of whisky?

In Scotland you can only use cask made from oak to mature Scotch whisky. This makes oak one of the most important components in the maturation of Scotch whisky. When the spirit goes into the cask it is a clear liquid with the flavours of new make created from malted barley and yeast during fermentation that then distil across. Once in the oak cask the spirit begins to interact with a series of complex chemical reactions that results in the spirit “extracting” flavour and colour from the oak. The skill is to match the type of oak and the previous contents of the cask with the distillery spirit characteristics for the period of maturation.

3. Why is European oak often associated with richer, spicier notes in whisky, while American oak tends to impart sweeter, vanilla-like flavours?

I don’t believe it is enough just to say European oak or American oak as there are over 600 species of oak in the world, and 500 species of oak in the Northern hemisphere alone. There are two species of European oak traditional used in maturing spirits: Quercus petraea and Quercus robur, which both provide very different flavours to the maturing spirit. For example, Quercus petraea contains more of the compound eugenol compared to Quercus robur. Eugenol, brings savoury spice flavours in particular clove aromas to the maturing whisky.

The most common North American oak species used for maturing whisky is Quercus alba which contains higher levels of a compounds call vanillin and hemicellulose. Vanillin brings those vanilla flavours to the maturing whisky and hemicellulose, particularly when toasted bring those sweet, butterscotch flavours.

4. Does the age of the oak used for barrel making affect the whisky, and if so, how?

The age of the oak and indeed, how the oak is dried, plays a very important role in its effect on the maturing whisky. It takes 80 to 160 years for an oak tree to reach maturation and before it can be felled.

Once felled the oak needs quarter sawn into what will be come the barrel staves and dried. The oak can be air dried or kiln dried depending on the type of cask and flavours required. For the type of flavours we are looking for air drying works best. The longer the oak is air dried the more the lignins in the oak breakdown into volatile phenols. This is why we specify 36 months air drying.

Also, the age of the oak cask and how many times it’s filled makes a huge difference to how the spirit matures and the influence of the oak on the spirit. The older the cask and the more times it has been refilled, the less the influence of the oak on the spirit.

5. How does the sourcing and sustainability of oak impact the whisky industry, and is there a trend toward more sustainable practices? Particularly when oak trees take decades to mature.

For oak forests to continue to exist and thrive sustainably forestry is a prerequisite. This requires planning 200 years ahead both for felling oak trees but also replanting. For example, the cooperage we work with in Colombia plant 5 trees for every one they fell. In France and the USA woodlands have been managed for centuries. It is essential that this long term management continues and develops with the global environment pressures that currently exist.

6. Are there any recent trends in the whisky industry where alternative oak species are being explored or used?

There is a global trend to identify and use different species of oak for maturing spirit, particular regional oaks for those newer distilleries around the world. After all there are 600 species of oak, the only issue is very few of them will make excellent whisky.

7. In your opinion, how will oak continue to evolve as a material for whisky aging in the future?

Oak is here to stay as a legal requirement for maturing Scotch Whisky but hopefully there will be more species of oak used for the maturation other than just the 3 traditionally used in Scotland.