Warehouses play a huge part in the whisky distillation process. In fact whisky develops 70% of its flavour while in the barrel.
Warehouses provide a home for the barrels as the precious liquid inside them ages and becomes the wonderful Whisky we all enjoy.
Before I wrote this article I had very little idea of the fact that there were in fact several different types of warehouses and not just the same old large grey building with shelves inside.
One of those if the Dunnage Warehouse. This is a traditional type of warehouse that is quite small in comparison to others. It is only tall enough to stack around three barrels and is created to provide top-notch air circulation.
These warehouses are usually built with a slate roof, stone walls and an earthen floor. The barrels are stacked on top of each other, three high.
Dunnage warehouses have been used to store whisky for centuries and have only relatively recently begun to be replaced with racked warehouses
Contrary to Dunnage warehouses, racked warehouses have thinner walls and atinroof. They are also a lot taller, allowing for more barrels to be stacked from 8-12 on racks with steel shelves. They are typical made from brick or concrete with a concrete floor.
A key factor in the differences between the warehouses is the effort that goes into switching the barrels. Dunnage warehouses are smaller and therefore are more likely to be labour intensive, since machinery does not fit well in the small rooms.
Racked warehouses on the other hand can be switched using forklifts and other types of heavy machinery.
The biggest difference is in temperature regulation, with racked warehouses allowing for more of a seasonal change due to their size and the thinner walls and tin roof. Despite this, both warehouses have similar average temperatures.
Temperature is vital to the aging process as it results in “cycles”. This means that in hotter temperatures the liquid expands allowing it more contact with the wood, through which it absorbs more flavour.
Temperature also controls how much liquid is lost to the angels share over the years. Higher temperatures mean more liquid evaporates out of the barrel.
It can be hard to say which is better for ageing Whisky and many distilleries in Scotland use dunnage warehouses as these are traditional.
It is important to consider that temperature depends a lot about climate and the outside climate of the warehouses will play a big factor, regardless of whether they are dunnage or racked.
Humidity is another factor to consider in the battle between dunnage and racked. Dunnage warehouses tend to have more humidity since they have an earthen floor that allows moisture to seep out and are smaller in size. Higher humidity results in slower maturation, which is preferable in the process of making Whisky.
Some say the dunnage are better since the barrels are stacked on top of one another, but again the effect that this has on taste is hard to qualify.
Some distilleries that use dunnage warehouses include Benromach, Knockdhu, Bruichladdich, Springbank and Kilchoman, whereas Scapa and Royal Brackla use racked, and Highland Park, Bowmore, Glenlossie, Glenglassaugh and Auchentoshan use both.
Both dunnage and racked warehouses have their merits and differences, it can be difficult to say which has more impact on flavour, especially since temperature and humidity tend to be quite similar. Perhaps it is telling that many distilleries use both dunnage and racked warehouses to mature their product.