Air and Kiln dried oak - what does it do, and why does it matter?
Benromach Distillery have released two new releases with a twist, allowing us to compare two whiskies comprising of the same unpeated spirit, but filled into American Virgin Oak Casks that have been prepped using different methods.
The drying process of the wood used for barrel-making has a massive impact on the flavours that will be transferred during maturation. There are two main ways of drying the wood - Kiln drying and Air drying - and both have been utilised in this double release.
Air drying can take up to 36 months and a minimum of 18 months, depending on the location of the cooperage. They are cut into staves and then stacked on pallets and left in the open air. During this period they are washed naturally by rainwater and dried by the sun until the moisture content is right for shaping.
This constant changing to the humidity of the wood reduces the risk of cracks or splits in the stave occurring during maturation. The seasoning process decreases the humidity in the wood from around 70-80% down to 15-18%.
Other factors affected by natural, or air drying are the enzymatic activity, ellagitannins composition and aroma composition.
During seasoning the wood is covered in a fungal flora, which penetrate the wood and release enzymes that affect the woods structure.
At the same time, ellagitannins can be lost due to various physical and chemical reactions including stave leaching (washing away by rainwater), oxidative degradation and the above fungal activity. These together can contribute to the decrease in astringent and bitter flavours.
Lastly, the impact on the aroma composition that occurs during air drying has a huge effect on the aromatic profile of the oak. Phenolic aldehydes (responsible for the vanilla flavours), and eugenol (giving spices such as clove and cinnamon) are increased during natural drying.
Overall, the idea of air (natural) drying the wood contributes to the oak quality and the quality of flavours transferred during maturation.
The process. can be accelerated by artificial (kiln) drying which take place in drying stores heated to dehydrate the wood. It is widely regarded that the air drying process provides better maturation as it has a greater impact on the composition of the wood, however the proof will be in the pudding of the individual glass.
This Air Dried expression of Benromach has been matured in casks that have, funnily enough, been air-dried. The theory here would be that we get more vanilla's, perhaps a little more spices and a better balance overall to the whisky.
Nose: Big vanilla, toffee fudge and sweet sugary notes. Balanced with a malty base of cereals, honey and museli. There's a little citrus peel - grapefruit - adding a dry note and preventing too much sweetness overwhelming the aroma.
Palate: A big, oily mouthfeel contributes to a sweet, creamy flavour. Butter, honey and vanilla, lemon drizzle cake and perhaps a little menthol. Dry notes of orange and oak and a little white pepper coming through.
Finish: Long, with peppery notes and oak. Dark chocolate and orange with green malt lingering.
It is important to highlight again that both these expressions have been matured in Virgin Oak casks, to allow the comparison to be made between the wood influence, and without the additional factor of previous maturation.
Nose: Much fruitier, green apples and pears, with fresh citrus flavours of lemon juice and also grapes. An intense aroma with a lot going on. It has an alcoholic spice on the nose that is more obvious than on the air dried expression.
Palate: A similar mouthfeel, big and oily, loading the palate with creamy notes. Again, more fruits. Boiled sweets and baked apple pie with cinnamon. There's some fruit salad in there, melons and grape with ripe banana. Benromach's biscuit base is there but it's bolder in here, more digestive biscuit than baked sponge.
Finish: A minty note comes through which is surprising as there was no indication of this on the palate! Toasted oak and a clove spice with some remnants of the apple pie lingering.
Unsurprisingly, these are both very different drams. Taking into consideration that every cask is different anyway, there is definitely an obvious difference in style to the two whiskies. If I had to choose one, the Air Dried expression just edges it. It feels more luxurious in the mouth and has a more balanced taste. Flavour-wise both are great, but the experience of drinking the Air Dried Casks stands above.