CHAPTER 4: Wood Chemistry and the Maturation of Whisky

Whilst the dominance of the wooden cask as a container for foods and liquids has diminished throughout the 20th century, to this day the global whisky industry is substantially reliant on the availability of oak casks. Originally, a convenient container for both wet and dry goods, including spirit, it became clear that the oak cask substantially improved the quality of the contained spirit. This is reflected in the common legislative restrictions regarding the minimum time that a spirit can be matured in oak before it can legally be called whisky. During the storage of spirit in cask, several processes occur that enhance the quality of the spirit. The so-called additive reactions are those that result in the extraction of compounds from the wood into the spirit. Subtractive reactions are those that result in a lower concentration of compounds than are in the new make spirit. Interactions can also occur between spirit compounds themselves, and between spirit and wood compounds. For instance, the release of acetate from oak and its formation via ethanol oxidation leads to increasing levels of ethyl acetate during maturation. The cumulative effects of these processes is a matured spirit with an array of positive attributes, contributing to the success of whisky as a leading global category in the distilled spirits arena. Recently there has been a growing interest in accelerating whisky maturation. Motion, heat, light and ultrasonics, have all been brought into play as options for moving spirit more quickly from new-make to final product.