Dimethyl sulphide is a well characterized off-flavour in the brewing industry. The thermal re-creation of dimethyl sulphide by the decomposition of dimethyl sulphide precursor in standardized wort is measured using pressure-controlled boiling processes at different temperatures. The results are used for the calculation of decomposition speed constants and Arrhenius activation energies. Using these data the re-creation of dimethyl sulphide during the wort production processes can be calculated and thereby optimized.
The current article describes the evaporation behaviour of dimethyl sulfide (DMS) in wort. All thermodynamic and technological basics and DMS data are listed. However, the article's target was not just the collection, editing and reviewing of information but also how to predict DMS evaporation behaviour from wort for different temperatures based on the data in the literature. For that particular purpose, a function was first set up that combined all of the information available on evaporation behaviour. In this context, the so‐called activity coefficient (γi) is of crucial interest. Owing to the broad basis of literature evaluated, the function set‐up as described can be deemed to be a current and accurate tool for predicting DMS evaporation behaviour, in general, as well as in particular for different boiling systems. Copyright © 2016 The Institute of Brewing & Distilling
This article deals with the impact of a vaporization surface in the brewing industry. The vaporization surface is deemed to have a positive impact on the evaporation quality of unwanted flavour components -especially dimethyl sulphide. Based on physicoprocedural considerations and trials, the current article deduces and verifies that an increased vaporization surface does not have an enhancing impact on evaporation quality.
This work is a continuation of preceding work in which limiting separation factors of important wort flavor components in water at 100 °C were determined. In unpublished experiments, the vapor-liquid equilibrium (VLE) of the same aromatic compounds was also researched at atmospheric conditions. No significant differences between the previous published limiting separation factors at 100 °C and the unpublished ones at atmospheric conditions could be observed. Because of this fact, the results of the measurements were used to calculate residue curves during the atmospheric boiling of wort. This study was only investigated at atmospheric conditions. A recirculating Gillespie-type still was used to determine the limiting separation factor (K ∞ ) for hexanal (x), 2-methylbutanal (x), 3-methylbutanal (x), and dimethylsulfide (x) in water (1x). Since the solutions were highly dilute (x < 10 -6 ), infinite dilution was assumed. As the investigated components do not have large absorbances in the UV region, they could not be analyzed by UV spectroscopy. Therefore, in contrary to the preceding work, they were analyzed by gas chromatography. As the boiling point of the solution only changed slightly at the given atmospheric conditions (∆T e 0.9 °C), the limiting separation factors were acquired assuming a constant average temperature of 98.55 °C. Thus, limiting activity coefficients were calculated at the same average temperature. The calculated limiting activity coefficient depends highly on the reliability of the vapor pressure data of the pure components.
The current article considers the question of whether vaporescence during wort boiling affects evaporation via the vapour side mass transport. Thereby the vaporization of unwanted flavour components (such as dimethyl sulphide or benzaldehyde) can be influenced negatively or positively, which affects the amount of energy needed. The question is pursued by pre‐calculation and experimental validation of the vapour side mass stream at the evaporation surface: for that purpose vaporescence trials were carried out in a plant trial, with both benzaldehyde and water as pure substances and a mixture of benzaldehyde and water in an infinite solution (xi < 10−6). Trial parameters were process temperature and volume stream of the gas phase. The results obtained by the trials with pure substances enable pre‐calculation of vapour side mass transport. Then, pre‐calculation is compared with the results of the mixture trials and thus verified. As a result it has to be stated that vaporescence in the brew houses is pre‐calculable and that the mass transport has an impact on the vaporescence at the vapour side boundary layer. Copyright © 2016 The Institute of Brewing & Distilling
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