ASSESSMENT OF SCOTCH WHISKEY QUALITY BY PYROLYSIS MASS-SPECTROMETRY AND THE SUBSEQUENT CORRELATION OF QUALITY WITH THE OAK WOOD CASK

In the production of Scotch whisky many factors are known to influence the final quality, including water, barley type, extent of peating and storage conditions. The most important contributor, however, is undoubtedly the oak cask in which maturation takes place. During the time period that the raw distillate spends in the cask, major changes occur in the chemical composition of the spirit, resulting in a product which has mellowed and become more acceptable to the palate. Traditionally, it has been the skill of the whisky blender which has been relied upon to assess the final quality of the mature spirit. In this study pyrolysis-mass spectrometry was examined as a possible rapid analytical method for the determination of Scotch whisky quality. The results showed that whisky quality from a particular distillery could effectively be discriminated using this technique. In addition, several characteristic features of quality were observed. A large proportion (97%) of the cooperage oak wood (Quercus sp.) required by the Scotch whisky industry is imported from the United States in the form of ex-bourbon barrels. Little is known however, about the physical features of oak and how they might affect the maturation potential of a whisky cask. Pyrolysis-mass spectrometry was used to examine how the growth rate of oak wood, and hence its earlywood to latewood ratio, might affect the resulting quality of the mature whisky spirit. The results suggested that a higher percentage of earlywood in a maturation cask was desirable for the production of well matured whisky, which in turn could be correlated with the slow growth rate of the oak tree.