Assessing the extent of charring and its impact on the whisky ageing process

The charring of a whisky barrel is a critical step at the beginning of the whisky ageing process. The extent of barrel charring and its resultant influence on the generation of phenols and esters that alter whisky flavour profiles is yet to be fully explored. In this study, American white oak ( Quercus alba ) was charred at nine different temperatures, 473–1073 K, and added to both neat ethanol and new make unaged whisky for 500 days. Through the tailoring of the surface area to volume ratio, ageing was focussed over the equivalent of a 250-day maturation period in a full-sized sherry butt, enabling nine chemical species, each associated with a unique flavour profile, to be tracked via regular sampling. The temperature at which the char was formed was not observed to directly alter the tracked flavour congeners, although trends concerning early ethyl ester formation are discussed. Notably, it was found that the presence of a char gradient, arising from the use of a blowtorch, increased the production of ethyl esters, particularly significant during the early stages of the aging process. We believe that additional studies investigating the influence of set heat exposures on char formation could further quantify this effect, enabling the impact of charring on whisky flavour profiles to be further understood. • Whisky was aged for 500 days using oak cubes charred at 9 different temperatures. • Char gradients rather than exposure temperatures had a greater impact on congeners. • A char gradient increased the production of ethyl esters within the whisky. • Phenol formation decreased for char produced using a blowtorch. • Conger formation was not linked to the temperature at which the char was formed.