Non-Isothermal Kinetic Models of Degradation of S-Methylmethionine

Dimethyl sulfide (DMS), which has a characteristic taste and aroma of cooked celery, is one of the most studied off-flavors in wort and beer. Although there have been many kinetic studies conducted with different wort boiling systems under isothermal conditions, the results are difficult to apply to the heating up process, in which the decomposition of the DMS precursor (DMS-P), S-methylmethionine (SMM) also takes place. And it is not easy to define the time of the beginning of wort boiling (t = 0) under isothermal conditions. In this study, the kinetics of thermal decomposition of SMM was studied using multiple dynamic measurements under non-isothermal conditions. Wort was heated to 140C in sealed test tubes with different heating rates (1–6 K/min). The activation energies (E_a) and the pre-exponential factors (A) for the decomposition of SMM were investigated using Coats–Redfern, Kissinger and Flynn–Wall–Ozawa method, respectively. The reaction mechanism follows first-order kinetics. The kinetic triple (E_a, A, G(α)) obtained from the non-isothermal method is compared with the results from isothermal method. In order to predict the formation of DMS and provide a better control during brewing process, a kinetic model was developed, which is applied to the heating up process and boiling process. Practical Applications: The assessment of a wort boiling system and the improvement of a brewing recipe should be based on chemical kinetic perceptions. Dimethylsulfide (DMS) is a typical leader substance and evaporation factor and also an off-flavor in wort. The knowledge about kinetic analysis on the formation of DMS is one of the important keys in order to control the brewing process and to guarantee the final beer quality. The results in this study can be used to calculate the optimal wort boiling to achieve the desired wort quality and final beer taste under atmospheric boiling conditions. In addition, the results can be used to improve the control of other heating parameters during heating and boiling of the wort.