THE PRESENCE OF TWO DIMETHYL SULPHIDE PRECURSORS IN MALT,THEIR CONTROL BY MALT KILNING CONDITIONS,AND THEIR EFFECT ON BEER DMS LEVELS

The precursor of dimethyl sulphide (DMS) which is formed during barley germination and is present in green malt differs from that present in malt kilned at high (> ～75°C) temperatures in that it cannot be metabolized to DMS by yeast. It is therefore termed ‘inactive’ precursor to distinguish it from the ‘active’ precursor present in kilned malt, which is metabolized to DMS by yeast. During malt kilning, inactive precursor is changed into the active form, but only at temperatures at which destruction of both precursors is also taking place. Therefore, for any kiln there is an optimum temperature range over which maximum conversion of inactive to active precursor can be combined with minimum destruction of both precursors. The DMS in beers brewed from green malt or malts kilned only at low (< ～70°C) temperatures is almost entirely the result of precursor destruction during wort boiling, final levels being governed not only by the conditions of boiling, but also by the extent of losses during fermentation and subsequent processing. In contrast, the DMS in beers brewed from malts kilned at higher temperatures is mostly formed during fermentation, and since beer DMS levels can be related to wort and beer DMS precursor levels, they can be better predicted and controlled. The method used for the measurement of total DMS precursor levels in malts is described in detail.     

ISOLATION AND PARTIAL CHARACTERIZATION OF THE DIMETHYL SULPHIDE PRECURSOR IN GREEN MALT,AND ITS EFFECT ON BEER DIMETHYL SULPHIDE LEVELS

The component from which dimethyl sulphide (DMS) is produced when green malt worts are heated has been purified and its effects on wort and beer DMS levels studied. The green malt precursor can be split into S-methylmethionine and an as-yet uncharacterized ninhydrin-positive component. When the purified precursor is added to worts derived from kilned malts, it is rapidly taken up by yeast, but there is no resulting increase in DMS production. DMS production during fermentation occurs with worts made from kilned malts but not with worts from green malt; however, this difference is not due to an inhibitor being present in green malt worts. The evidence suggests that malt kilning affects the nature as well as the amount of DMS precursor in malts.     

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%。     

精酿啤酒专用麦芽的研究进展

在工业啤酒日趋饱和的大背景下,精酿啤酒在中国受到越来越多消费者的喜爱,并呈现出广阔的成长空间。麦芽作为精酿啤酒重要原料之一,其品质优劣决定了啤酒品质的好坏。该文结合当前精酿啤酒专用麦芽的应用研究,总结、归纳了精酿啤酒酿造用麦芽的基本种类、制麦工艺、麦芽风味物质及麦芽主要成分对啤酒品质的影响,最后阐述了精酿啤酒专用麦芽对麦芽加工工业和精酿啤酒制造业的重要意义,并对精酿啤酒专用麦芽的前景进行了展望。     

有色特种麦芽

有色特种麦芽赋予啤酒特征性的色度和风味,其应用满足了消费者对不同风味啤酒的需求,论述了有色特种麦芽的种类,风味特征及生产的啤酒风味特征,阐明了其焙烧民品有色麦芽的分析指标和在啤酒中的应用。     

MALTING CHARACTERISTICS OF FINGER MILLET,SORGHUM AND BARLEY*

The malting characteristics of the finger millet variety Imele (FI), sorghum varieties Andivo (SA) and Ingumba (SI) and the barley variety Research (BR) were compared in relation to the brewing of traditional African opaque beer as well as conventional lager beer. The investigations include (a) the effect of steeping and germination conditions, (b) the influence of gibberellic acid and kilning temperature on the activity of important brewing enzymes and (c) an appraisal of the brewing potential of the worts obtained. FI, SA and SI malts were considered unsuitable as barley malt extenders for conventional lager beers, but FI and possibly SI malts would be suitable for tropical lager beer manufacture.     

Influence of malt browning degree on lipoxygenase activity

The development of off-flavour in pale beer is generally attributed to the oxidation of the intermediate products of lipid degradation catalysed by lipoxygenase during mashing. This paper deals with the effect of speciality malts, having different browning levels, on malt lipoxygenase. The results obtained showed that lipoxygenase activity, which was found to be present only in the pale malt, was affected by mashing temperatures above 63 °C and by the presence of Maillard reaction products in the speciality malts. In particular, the addition to pale malt of speciality malts, having high inhibitory capacity towards lipoxygenase but low colouring potential, was effective in reducing the off-flavour development in pale beer.     

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.     

MALTING AND BREWING WITH BARLEYS HAVING BLUE ALEURONES

Blue aleurones in barley are associated with elevated levels of polyphenolic materials such as anthocyanins and anthocyanidins. A rapid method has been developed for assessing the anthocyanin content of barleys, malts and worts. Malts were prepared from a range of barleys, some of which had intensely blue aleurones, while others were only slightly blue or showed no visible pigmentation. The malting quality of barley was not affected by aleurone colour and ales and lagers of sound flavour as well as acceptable analytical parameters were brewed from malts having pronounced blue aleurones. In some cases sweet worts prepared from blue aleurone malts had a slight pinkish tinge, but this disappeared during wort boiling, and beer colours were normal. Levels of anthocyanins in barley correlated with those in malt and in wort. However, the concentration of anthocyanins was unrelated to the amount of anthocyanogens or total polyphenols. High anthocyanin levels in either barley or beer had no deleterious effects on beer flavour or the rate of haze development.     

Optimised quantification of the antiyeast activity of different barley malts towards a lager brewing yeast strain

The brewing of beer involves two major biological systems, namely malted barley (malt) and yeast. Both malt and yeast show natural variation and assessing the impact of differing malts on yeast performance is important in the optimisation of the brewing process. Currently, the brewing industry uses well-established tests to assess malt quality, but these frequently fail to predict malt-associated problem fermentations, such as incomplete fermentations, premature yeast flocculation (PYF) and gushing of the final beer product. Antimicrobial compounds, and in particular antiyeast compounds in malt, may be one of the unknown and unmeasured malt factors leading to problem fermentations. In this study, the adaptation of antimicrobial assays for the determination of antiyeast activity in malt is described. Our adapted assay was able to detect differing antiyeast activities in nine malt samples. For this sample set, malts associated with PYF during fermentation and gushing activity in beer showed high antiyeast activity. Both PYF and gushing are malt quality issues associated with fungal infection of barley in the field which may result in elevated antimicrobial activity in the barley grain. Also, two more malts that passed the normal quality control tests were also observed to have high antiyeast activity and such malts must be considered as suspect. Based on our results, this assay is a useful measure of malt quality as it quantifies the antiyeast activity in malt which may adversely impact on brewery fermentation.     

THE INFLUENCE OF MASHING CONDITIONS ON WORT AND BEER QUALITY

From a comparison of the performance of ale and lager malts mashed by constant temperature infusion, by temperature programmed infusion, and by decoction procedures it emerges that malt modification and the pattern of kilning are as important in determining the composition of wort as are the mashing conditions. Worts with appropriate levels of amino and total nitrogen and of fermentable sugars may be obtained by selecting lightly-dried well-modified malts and mashing with a constant temperature infusion rather than by using less modified malt in conjunction with more complex mashing programmes. Ale malts yield worts of lower pH which is reflected in a slight reduction in hop utilization. Head retention is improved by the use of undermodified malts but colloidal stability is improved when well-modified malts are used. In the case of well-modified malts a high final curing temperature is not a prerequisite for achieving good colloidal stability in beer.     

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     

Roasting of malt and xanthohumol enrichment in beer

The use of commercial roasted malts increases the content of the hop polyphenol xanthohumol (XN) in beer. This carrier effect is caused by high molecular melanoidins from roasted malt. Three roasting trials with different malts were performed in order to study the development of XN enrichment of wort and beer in laboratory and brewing trials. Different colour measurements, malt and flavour analysis, radical formation and antioxidative activity of selected samples were carried out. Furthermore, sensory tests of beers were conducted. During roasting the XN and isoxanthohumol enrichment in wort and beer rose with the roasting intensity of malt until it reached a maximum. The XN content in wort increased linearly with the colour of wort made from the malt samples. In PVPP-treated worts and in filtered beers, the XN content increased exponentially with the colour. After passing through a maximum, both the colour value and XN content in wort and beer decreased. Interestingly, the colour losses were more intensive than the losses of XN in worts and beers. The development of radical formation and the reducing power was linked during roasting. That means reducing groups of melanoidins are responsible for reducing power and prooxidative properties of malts. These functional groups of melanoidins are involved in the development of XN enrichment properties, because a linear correlation between these parameters was found. In conclusion, the roasting regimes showed potential for the development of special malt for the XN enrichment in beer- or malt-based beverages in late roasting stages. The use of this special malt brings more XN with less coloured malt in beer.     

Impact of Dark Specialty Malts on Extract Composition and Wort Fermentation

Dark specialty malts are important ingredients for the production of several beer styles. These malts not only impart colour, flavour and antioxidative activity to wort and beer, they also affect the course of wort fermentations and the production of flavour‐active yeast metabolites. The application of considerable levels of dark malt was found to lower the attenuation, mainly as a result of lower levels of fermentable sugars and amino acids in dark wort samples. In fact, from the darkest caramel malts and from roasted malts, practically no fermentable material can be hydrolysed by pilsner malt enzymes during mashing. Compared to wort brewed with 50% pilsner malt and 50% dark caramel malt or roasted malt, wort brewed with 100% pilsner malt contained nearly twice as much fermentable sugars and amino acids. Reduced levels of yeast nutrients also lowered the fermentation rate, ranging from 1.7°P/day for the reference pilsner wort of 9 EBC to 1.1°P/day for the darkest wort (890 EBC units), brewed with 50% roasted malt. This additionally indicates that lower attenuation values for dark wort are partially due to the inhibitory effects of Maillard compounds on yeast metabolism. The application of dark caramel or roasted malts further led to elevated levels of the vicinal diketones diacetyl and 2,3‐pentanedione. Only large levels of roasted malt gave rise to two significant diacetyl peaks during fermentation. The level of ethyl acetate in beer was inversely related to colour, whereas the level of isoamyl acetate appeared to be affected by the use of roasted malt. With large levels of this malt type, negligible isoamyl acetate was generated during fermentation.     

Impact of colour adjustment on flavour stability of pale lager beers with a range of distinct colouring agents

The impact of colour adjustment on the flavour stability of five pale lager beers with a range of colouring agents such as specialty malts, colouring beer and artificial caramel colourant was investigated. The research focused on determination of the endogenous anti-oxidative potential (EAP) of the beer samples using a novel Electron Spin Resonance (ESR) method. The results were correlated with the concentration levels of a portfolio of compounds formed during beer ageing, which were detected and quantified by GC–MS. The beer samples were also assessed by the ICBD sensory panel. Additionally, the quantification of organic radicals of the specialty malts and the roasted barley were conducted by ESR (whole intact kernel and milling fraction measurement). Based on the results of this holistic approach, a colouring agent was identified that enhanced the flavour stability of pale lagers based on the final beer’s physical-, chemical-, and sensory-properties.     

Immunochemical determination of gluten in malts and beers.

The gluten content in different varieties of barley and malts, and in different types of beers, was determined by a 'sandwich' enzyme immunoassay (RIDASCREEN Gliadin kit). The gluten levels in barley wheat, rye and spelt malts ranged 18.8-45.0, 44.0-68.0, 41.6 and 21.2 g kg-1, respectively. When various types of beer were compared, the gluten concentration increased as follows: alcohol-free beer (<3.0), lager beers (<3.0-8.7 mg l-1), stouts (9.0-15.2 mg l-1) and wheat beers (10.6-41.2 mg l-1). When 10 Czech lager beers were analysed, using both sandwich and competitive ELISA, the results showed that the latter method provided values several times higher than the former. Gluten balance was carried out during the brewing process, starting from the raw materials and terminating at the final beer. Gluten levels decreased due to precipitation during the mashing process, primary and secondary fermentation and, lastly, as a result of adsorption during beer stabilization. The gluten content in beer is, thus, approximately three orders of magnitude lower than in the raw malt.     

不同种类麦芽对下面发酵啤酒酿造风味的影响

为了从源头控制下面发酵啤酒的发酵生产并提高其品质,通过啤酒发酵模拟体系,系统评价英国麦芽（Eng）、加拿大麦芽（Can）和德国麦芽（Ger）对下面发酵啤酒酿造风味的影响。分别测定了3种麦芽的品质指标及所酿啤酒的理化指标;并采用顶空固相微萃取（HS-SPME）和气相色谱质谱联用（GC-MS）法检测了所酿啤酒中风味物质组成和含量上的差异。结果表明,加拿大麦芽的库尔巴哈值（45%）、浸出率（≥77%）、糖化力（414 WK）和α-氨基酸态氮（118 mg/L）等品质指标和酒精度（2.97%vol）、原麦汁浓度（8.63 °P）、实际浓度（2.76%）、外观浓度（1.17%）、实际发酵度（67.97%）和外观发酵度（86.41%）等所酿啤酒的理化指标适中,啤酒中风味物质种类多样（75种）、相对含量丰富（271.82%）、比例协调,是最适合酿造Lager啤酒的麦芽种类。该结果可为高品质啤酒的工业化生产提供理论依据。     

A study on malt modification,used as a tool to reduce levels of beer hordeins

Storage proteins from barley, wheat and rye are toxic to gluten sensitive consumers. These consumers include those suffering from coeliac disease, which account for up to 1% of the global population, and non‐coeliac gluten sensitivity that may affect even greater numbers of the population. Codex Alimentarius has published guidelines and limits of gluten in gluten‐free foods, which are applied in Europe, and similar guidelines apply in the rest of the world. The storage proteins present in barley are hordeins. These proteins are broken down and used by the plant as a source of amino acids during germination and growth of the barley embryo. The objective of this study was to extend the germination stage of the malting process and look at the effect on beer hordeins. Standard MEBAK methods were used to develop an extended malting process and produce three different malts, germinated for 3, 5 or 7 days. The quality of malt was assessed and model beers were produced from each malt to test the effect of modification on levels of beer hordeins. Malt germinated for 7 days produced beer 18 mg/kg hordeins corresponding to a reduction of 44% compared with the beer made from malt germinated for 3 days characterized by a hordein content equal to 32 mg/kg. The malting loss was increased during the 7 days of germination but otherwise all malts were of high quality. The results showed that malting conditions have a significant impact on beer hordeins. Copyright © 2018 The Institute of Brewing & Distilling     

New approach to the production of xanthohumol‐enriched beers

Xanthohumol is a hop polyphenol with proven positive effects on human health. The aim of this work was to use special malts (roasted malt and melanoidin malt) for the preparation of high‐gravity sweet worts with an extremely high xanthohumol content. The solubility of xanthohumol was higher in sweet worts prepared from roasted malts than from Pilsen or melanoidin malts. This sweet wort (xanthohumol ~20 mg L^?1) was used for the preparation of xanthohumol‐rich beer. The importance of melanoidins in xanthohumol solubility was also examined. Isomerization reactions occurring at increased temperatures is one of the main reasons for the loss of xanthohumol in the brewing process and therefore the most appropriate temperature for addition of xanthohumol products to sweet worts was determined. The influence of filtration and stabilization materials (diatomaceous earth, polyamide sorbents and tannic acid) on the concentration of xanthohumol in enriched beer was also examined. Only a small effect of these materials was shown in xanthohumol‐rich dark beers, with the exception of tannic acid, which removed a significant amount of this polyphenol. Copyright © 2013 The Institute of Brewing & Distilling.     

Foam inhibitors from specialty malts

Although there are product‐to‐product differences, the majority of the crystal and caramel malts tested have been shown to have a net destabilizing impact on foam. A foaming test using a model beer has been developed to quantify the magnitude of this inhibitory effect. Lipid analysis using thin‐layer chromatography reveals that there are elevated levels of triglycerides in problematic malts. There also appear to be oxidized lipids in the specialty malts, probably produced in the heating stage of malt production with higher levels in more intensely heated products. However some specialty malts, such as black malt, while containing such foam‐negative entities, do display superior foaming properties, probably because they develop even more powerful foam‐positive components in the severe heating events. Copyright © 2014 The Institute of Brewing & Distilling