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2-Methylbutanal (2-MB) and 3-methylbutanal (3-MB) are highly volatile compounds and typical beer aging compounds. The development of a kinetic model of the formation of 2- and 3-MB is useful to estimate the wort flavor during the wort boiling and the flavor stability of beer. A model experiment was performed, using d-glucose/ d-maltose and l-leucine/isoleucine to study Maillard reaction in a buffer solution of a pH value of 5.2. The simulated solution was heated at different time (0-360 min) and temperature (90-130 °C). The concentrations of d-glucose/ d-maltose, l-leucine/isoleucine and 2- and 3-MB were determined by HPLC and GC. This kinetic model is based on the correlation between the concentration of 2- and 3-MB and the concentration of l-leucine/isoleucine. In this paper, the multistep formation method of 2-MB/3-MB is simplified to a three-step reaction. The kinetic parameters Ea, A and k were calculated for each reaction step. It was found that the formation of 2- and 3-MB has a sequence like this: GL > ML > GI > MI. The total activation energies for the formation of 2- and 3-MB are ranging from 107.87 to 178.88 kJ/mol. The developed kinetic model gives a good fit with the experimental data. This study is useful for the control of the wort quality during the boiling process and could also be interesting for food and beverage industries. Practical Applications Maillard reactions are responsible for the formation of most wort flavors. In addition to this there exist intermediates, which lead to the development of off-flavors during shelf life. The 2- and 3-MB are the Strecker aldehydes and have typical wort flavors. Wort boiling is not only the midpoint of the brewhouse, it is also one of the most important steps in producing an excellent beer. The kinetic study of the formation of 2- and 3-MB is very useful for the control of wort boiling parameters. This result is helpful to calculate a suitable wort boiling time for different raw materials under brewing process conditions. [ABSTRACT FROM AUTHOR]

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 ( Ea) 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 ( Ea, 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. [ABSTRACT FROM AUTHOR]