Analysis and origin of characteristic aroma of whisky matured in ex-red wine casks

Abstract

Traditionally, ex-bourbon and ex-Sherry casks are used for maturation of Scotch whisky. Recently however, maturation in other types of cask such as ex-red wine casks or rum casks has become popular as a method to extend the flavour profile. For example, whisky matured in ex-red wine casks has a characteristic, strawberry-like, sweet and sour aroma. We have investigated the key components of the characteristic sweet aroma imparted during ex-red wine cask maturation using fractionation techniques and mass spectrometry-olfactometry (GC/MS-O). The results of fractionation experiments showed that the sweet aroma was found in the neutral and mid-polar fraction. The results of GC/MS-O analysis of the neutral and mid-polar fraction showed that 2-heptanone, 2-nonanone, 1,1-diethoxyethane, diethyl succinate, γ-nonalactone and trans-oak lactone provided sweet, fruity and green aromas and were present at higher concentrations in ex-red wine cask matured whisky compared to remade hogshead cask matured whisky. In addition, spiking tests revealed that whilst each of these compounds individually contributed to the sweet character, it was the combination of all these compounds that gave more complexity and was closer to the target ex-red wine cask character. Furthermore, whilst acidic compounds such as acetic acid, propionic acid, ethyl lactate and 3-hydroxy-2-butanone did not have a sweet aroma, they did enhance this aroma and the ex-red wine cask maturation character. Therefore, these results suggest that the characteristic aroma of whisky matured in ex-red wine casks is complex and attributable to several different compounds.