Equilibrium of esterification in Chinese distilled liquor (Baijiu) during ageing

Different Baijiu varieties are characterised by their specific flavours and ester aromas. These flavours originate from the process of esterification during long-term ageing. Despite their wide popularity and long history, the mechanism of esterification during ageing has not been experimentally demonstrated. This study aimed to elucidate the esterification mechanism experimentally to promote advances in the ageing technology for Baijiu and to help advance the Baijiu brewing industry to transform it into a carbon-neutral industry. In this study, traditional acid-catalysed conditions were applied and esterification during ageing was accelerated. Equilibrium constants were obtained for the major esters via thermodynamic calculations and these constants were corrected using the experimental results. These corrected constants can predict the acid and ester contents of the liquor during ageing. Thus, the results can also help standardise Baijiu brewing technology.