Explanation for the increase in free dimethyl sulphide during mashing

Temperatures during mashing range from 50 to 80 °C. An interesting observation is that not only desired flavours but also some unwanted components, such as the flavour compound dimethyl sulphide (DMS), are extracted and solved. During the mashing process, the content of DMS increases, which cannot be explained by the temperature‐dependent decomposition of its DMS precursor. The current article deals with this particular question and offers an explanation by application of thermodynamic basics. Copyright © 2015 The Institute of Brewing & Distilling     

Validation and discussion of the vaporization surface

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 physico‐procedural considerations and trials, the current article deduces and verifies that an increased vaporization surface does not have an enhancing impact on evaporation quality. Copyright © 2015 The Institute of Brewing & Distilling     

THE IDENTITY OF AN INHIBITOR IN WORT OF DIMETHYL SULPHOXIDE REDUCTASE FROM YEAST

Wort contains a substance which inhibits the reduction of dimethyl sulphoxide by yeast. The inhibitor has been purified by dialysis followed by chromatography on Sephadex G-15 and Dowex 50. It has been identified as methionine sulphoxide.     

THE USE OF RADIOACTIVE LABELLING TO DEMONSTRATE THE PRODUCTION OF DIMETHYL SULPHIDE FROM DIMETHYL SULPHOXIDE DURING FERMENTATION OF WORT

During fermentation, yeast reduced [¹⁴C] dimethyl sulphoxide (DMSO) to yield radioactive dimethyl sulphide (DMS) even under conditions in which no net formation of DMS could be demonstrated by GLC analysis. It was confirmed that most DMS is produced during fermentation of lager worts at 8°C.     

CAMBRIDGE PRIZE LECTURE DIMETHYL SULPHIDE—ITS ORIGIN AND CONTROL IN BREWING

The fate of dimethyl sulphide (DMS) and its precursors, S-methylmethionine (SMM) and dimethyl sulphoxide (DMSO), in the malting and brewing processes, has been studied on both a laboratory and a production scale. The information gained has been used to show how the level of DMS in beer may be controlled. The principal determinant of the beer DMS level was the SMM present in malt. DMSO was not a significant precursor of DMS in normal lager production.     

THE INFLUENCE OF ASSIMILABLE NITROGEN COMPOUNDS IN WORT ON THE ABILITY OF YEAST TO REDUCE DIMETHYL SULPHOXIDE

Dimethyl sulphoxide (DMSO) reductase activity increased at the end of the growth cycle of Saccharomyces cerevisiae NCYC 240 on complex medium. On defined medium, DMSO reductase and thioredoxin reductase activities and thioredoxin were all elevated in cultures limiting in nitrogen, but not in nitrogen-sufficient cultures. In nitrogen limiting cultures it was also shown that the reduction of DMSO (measured as disappearance of [¹⁴C] from the medium) was much increased compared with conditions of nitrogen excess. This applied whether ammonium or glutamate was the limiting nitrogen source. When methionine was used as the limiting nitrogen source, DMSO reduction was higher still. Methionine-limited cells accumulated [¹⁷C] methionine much more rapidly than did cells from methionine-sufficient cultures, and [¹⁴C] methionine sulphoxide could be identified in the cells after 1 min incubation with labelled methionine. It is concluded that DMSO reductase activity is controlled by nitrogen catabolite repression and may be involved in methionine uptake by yeast. The amino nitrogen content of wort will in consequence have an important effect on levels of dimethylsulphide (DMS) produced during fermentation.     

THE RELATIONSHIP OF DIMETHYL SULPHIDE LEVELS IN MALT,WORT AND BEER

The half-life for the conversion of malt dimethyl sulphide (DMS) precursor to free DMS has been determined at various temperatures and pH values. At pH 5·2 the half-life of the precursor in wort (S.G. 1·060) at its boiling point is 38 min, and is doubled for each 6°C fall in temperature. At pH 5·5 the half-life at the boiling point is 32·5 min. Knowing the stability of the precursor at the various temperatures in the brewing process, the extent of conversion to free DMS in wort at pitching can be predicted for malt of a given precursor content and for a given set of process conditions. The results of DMS analyses of samples taken during brewery trials are in reasonable agreement with the predicted values. This work involved infusion mashing only, but the same principles apply to decoction mashing. The fate of precursor and free DMS during fermentation and conditioning has been followed on a production scale. With some brews, where high levels of free DMS were present at pitching, much free DMS was lost during fermentation. Also, precursor DMS reappeared in the beer after a few days and there was some increase in the level of free DMS. The DMS precursor in green malt has been isolated by ion-exchange and gel-filtration chromatography. A preparation has been obtained which has 0·6 mol potential DMS per mol amino nitrogen. Thin layer chromatography showed that the preparation and its hydrolysis product had the same R_f values as S-methylmethionine and homoserine respectively.     

Optimization of the vaporization of flavour components during wort boiling in the brewery by implementing a rectification column

Boiling the wort is an energy‐intensive step during beer production. The central objective of the process is the evaporation of unwanted flavour components, above all the flavour component dimethyl sulphide (DMS). To reduce the required overall evaporation, a recent development involves the insertion of a stripping column into the vapour discharge vent of the wort kettle in which the wort is directed from the kettle against the ascending vapour. The calculation by means of procedural fundamentals and the validation of the process in a large brewery are the subject matter of this article. Process improvement in comparison with conventional boiling systems is documented. Copyright © 2017 The Institute of Brewing & Distilling     

THE REDUCTION OF DIMETHYL SULPHOXIDE TO DIMETHYL SULPHIDE DURING FERMENTATION

Dimethyl sulphide (DMS) produced by yeast during fermentation is formed from dimethyl sulphoxide (DMSO) rather than from S-methyl methionine (HADMS). All the yeasts and one of the two spoilage organisms examined formed DMS from DMSO. In fermentations at 8°C only 13–21% of the DMSO is reduced to DMS by yeast and the extent of conversion is greatly decreased by raising the fermentation temperature. The amount of DMS formed increases as the gravity of the wort is raised but is also dependent on the fermentable sugar employed. There is therefore no simple correlation between DMSO content of the wort and DMS formation.     

Effects of nitrogen application on malt modification and dimethyl sulfide precursor production in two Japanese barley cultivars

BACKGROUND: Nitrogenous components have a great influence on both malt and beer qualities. Barley storage proteins are degraded during the germination process, in which amino acids and small peptides are released. Some of these compounds relate to dimethyl sulfide precursor production in the malting process. In this study, barley and malt qualities were investigated using two Japanese barley cultivars, Sukai Golden and Mikamo Golden, with several different nitrogen (N) treatments. RESULTS: Nitrogen top‐dressing treatments efficiently increased N and sulfur (S) concentrations in grains. A difference in malt modification was induced by these treatments without any change in protease activity in malts. S‐Methyl methionine (SMM) concentration in malt of Sukai Golden with low‐N treatment was 1.8–2.1 times higher than that with higher‐N treatments. Methionine concentration in malts was not significantly affected by N treatments of both cultivars, while grain S level was not consistent under any treatments. CONCLUSION: Results show that low‐N treatment increases SMM concentration in malts despite major S‐containing amino acids of malts being not highly affected by the difference in nutrient status of grains. Further investigations are necessary into aspects of both metabolic profiles in barley germination and SMM degradation in the kilning process. Copyright © 2008 Society of Chemical Industry     

Effects of hydrogen sulphide on quality and antioxidant capacity of mulberry fruit

Here we investigated the effect of hydrogen sulphide (H₂S) on postharvest quality of mulberry fruit and possible underlying mechanisms. Endogenous H₂S content first increased after harvest and then decreased sharply with the process of ripening and senescence. A fumigation with H₂S released from 0.8 mm NaHS solution could significantly enhance the endogenous H₂S content by increasing the activities of D‐cysteine desulfhydrase and L‐cysteine desulfhydrase. NaHS could significantly slow down the ripening rate of mulberry fruit and reduce the respiratory intensity and anthocyanin content. Moreover, H₂S fumigation was able to obviously delay or slow down the decreases in soluble protein, titratable acidity and ascorbate contents. Further results showed that activities of representative antioxidant enzymes in H₂S‐treated sample were higher than those of control samples during storage, resulting in a decrease in superoxide anion production. Together, these results clearly indicate that H₂S fumigation has a potential role in the preservation of mulberries.     

AN ALTERNATIVE METHOD FOR THE DETERMINATION OF DIMETHYL SULPHIDE IN BEER

A method for the determination of dimethyl sulphide (DMS) in beer and for total DMS precursor in malt is described. The DMS was extracted into chloroform and determined by glass capillary gas liquid chromatography (GLC) using a flame ionisation detector (FID) and diethyl ether as an internal standard. Errors arising from the use of ‘head space’ sampling were thereby avoided. The reproducibility of results and the recovery of DMS at the 100 ppb level were satisfactory but less so at levels below 50 ppb. Beers produced in a pilot brewery from malts containing high levels of total DMS precursor were not found to contain correspondingly high levels of DMS.     

Determination of dimethyl sulphide in beer and lager

A gas chromatographic method is described for the determination of dimethyl sulphide in beer. The peak height of the dimethyl sulphide is compared with that of an n-butanol standard and the concentration calculated using their relative response factors. When authentic dimethyl sulphide was added to beer good recoveries (99% average) were obtained. Determination of the reproducibility from duplicate analyses of beer samples gave an average coefficient of variation of 7.7 % for the concentration range of 0-35 μg/l.     

新型防腐剂DMF的催化合成

研究以钨硅杂多酸为催化剂,马来酐和甲醇为原料合成富马酸二甲酯(DMF)。反应的最佳条件是:马来酐和甲醇的物质的量比为1∶6、催化剂用量为马来酐质量的8%、反应时间6h,产率达94.4%     

啤酒中二甲基硫的形成与控制

二甲基硫是影响啤酒风味的极重要物质。介绍在硫的形成途径和影响因素,及控制啤酒中二甲基硫的形成。     

Effect of antioxidants on dimethyl sulphoxide reduction and impact on dimethyl sulphide formation during beer storage

Dimethyl sulphide (DMS) can be important in beer aroma. Although primarily formed during wort boiling, it can evolve during fermentation by reduction of its oxidation product dimethyl sulphoxide (DMSO). In this study, a number of antioxidants – sulphite, thiols [l ‐cysteine, l ‐glutathione (GSH)], gallic acid and ascorbic acid – were tested on DMSO reduction and DMS formation in a buffered model solution [pH 4.3, 5% (v/v) ethanol] together with a Pilsner type beer. In the model solution, significant DMSO reduction and DMS formation were observed for sulphite and the thiols l ‐cysteine and GSH. Ascorbic acid and gallic acid were not capable of reducing DMSO. During beer storage at 28°C, the highest DMS formation was found with the combined addition of sulphite, GSH and DMSO followed by sulphite/DMSO and GSH/DMSO. In conclusion, the reaction mechanisms of DMSO reduction and their relevance to DMS formation during beer storage are discussed. © 2018 The Institute of Brewing & Distilling     

纺织品中富马酸二甲酯测定的不确定度评定

依据GB/T 26713—2011《鞋类化学试验方法富马酸二甲酯的测定》,采用超声波萃取和气相色谱-质谱(GC-MS)联用法对鞋类纺织材料中富马酸二甲酯含量进行测定。分析了鞋类纺织材料中富马酸二甲酯测定过程的不确定度的来源,并对不确定度各个分量进行评定、合成,给出了该方法测定结果的合成不确定度和扩展不确定度,通过评定不确定度保证了分析测量的有效性。     

Methyl-S-methionine sulphonium salt: A precursor of dimethyl sulphide in cacao

Chromatographic evidence is presented to show that a methyl-S-methionine sulphonium salt is present in fermented and dried cacao. It is extremely labile and readily decomposes to dimethyl sulphide which contributes to chocolate aroma.     

啤酒酿造中二甲基硫、甲基蛋氨酸、二甲基亚砜含量的变化与控制

为控制啤酒风味物质二甲基硫（dimethyl sulfide,DMS）的含量,实验运用气相色谱-氢火焰离子化检测器测定了15 种国内市售啤酒样品DMS的含量,并研究了啤酒酿造中DMS、甲基蛋氨酸（S-methylmethionine,SMM）、二甲基亚砜（dimethyl sulfoxide,DMSO）的含量变化。结果表明,抽取的国内市售啤酒样品中有47%的样品DMS含量超出60 μg/kg,特别是爱尔啤酒（Ale）中71%的样品DMS含量超出60 μg/kg,最高值达到105 μg/kg;实验抽检10 种国内市售麦芽DMS、SMM、DMSO含量,不同麦芽间DMS与二甲基硫前驱体（dimethyl sulfide precursor,DMSP）差异较大,差异最高达160%,且多数小麦芽的DMS与DMSP含量低于澳麦芽。实验研究了麦汁煮沸、发酵过程中的DMS及DMSP含量的变化,在100 ℃、pH 5.6时,麦汁煮沸40 min后DMS含量比初始含量降低92%,SMM的半衰期为31 min。发酵过程中DMS含量在发酵旺盛期时有明显的下降,最高下降41%。