Maturation in Casks

The identification of different flavors is done with physiochemical methods. Our senses are so sensitive that even smallest amounts can account for big differences in taste. Various substances like esters, tannins, lactones etc. in ppm (parts per million) and ppb (parts per billion) are measured by researchers. These small quantities are hard to grasp.

The taste of the whisky can be enormously influenced by smallest changes in the maturation process. Let's first have a look at the wooden cask which is the most important component of the maturation process.

1. The Wood
   A small masterpiece of craftsmanship is a wooden cask. More and more machines are used by coopers today but the actual manufacturing is still done by hand.

Only oak wood is suitable for cask production. The resin in softwood prevents the cask from breathing. Some unpleasant flavors are emitted by other types of wood that make the whisky awkward or even unenjoyable. The ideal wood is Oak wood from trunks with an age of 70 to 200 years.

1. Different Casks
   The size of the casks influences the maturation process along with the type of wood and the thermal treatment. The maturation of whisky is faster in small casks since the surface area is bigger in relation to the content and also the exchange of substances between wood and whisky happens faster.

2. Re-use of Casks
   A considerable part of the overall costs of whisky production (about 10% to 20%) accounts for production costs of casks and along with this increased demand for casks in the whisky industry is also a reason to the rise of cask prices. That's why the Scots use casks several times. Casks can be used three to four times, and then the wood has lost most of its flavours.

Rejuvenation is the future. The life of the cask can be prolonged significantly with little effort.

1. Maturation and Taste
   During maturation there are three fundamentally different effects in the cask that play a role.
   • Subtractive Maturation
   New make whisky has a tangy, metallic taste and if you ever tasted a sample from a pot still or a spirit safe, you will always remember this rather unpleasant taste.
   • Additive Maturation
   Initially it's a general wood flavor but especially vanilla, toffee and oak, but, with increasing maturation time the whisky takes up flavors from the cask
   • Interactive Maturation
   The taste of whisky is not only affected by maturation and the cask character but the basic character of a whisky is shaped by the special distillation and the malt that has been used. Interactive maturation is when distillery character and cask influence join to form a harmonious whole.

2. The Cask Determines the Result
   The various cask influences during interactive maturation is shown by green lines. Since the alcohol in the whisky extracts flavors from the cask, we're actually dealing with dissolution processes. First the curves rise steeply and then flatten more or less strongly and only the middle curve is more or less ideal. The ideal combination of cask and distillery character is interactive maturation.