Kinetic studies of main wort flavor compounds and iso-α-acids during wort boiling: a review

During wort boiling, the biochemical and physical reactions in wort give beer its characteristics flavors, color, and bitterness. These reactions are affected by many process factors, such as temperature, boiling time, and concentrations of substances in raw materials. The concentrations of the wort flavor compounds influence not only the quality of wort and finished beer, but also the shelf life. Therefore, it is necessary to control the process parameters as well as the main wort flavor components in wort and beer. Kinetic knowledge provides a basis for the simulation of the boiling process and prediction of the formation and evaporation rate of main wort flavor components. Using the kinetic modelling can achieve a decrease of the boiling time, save energy and produce good beer quality. By comparison with the advanced kinetic studies in chemistry or other food sciences, in brewing science the kinetic investigation remains in its initial stage. This paper summarizes the existing kinetic modelling and kinetic parameters of evaporation and formation of main wort flavor components (e.g., 2-methylbutanal, 3-methylbutanal, DMS, hexanal, 2-phenylethanol, 2-phenylethanal) and the formation and degradation of iso-α-acids.