A Method to Detect Anti‐metabolic Factors in Fermentations

Premature yeast flocculation (PYF) has been described as the rapid settling of yeast cells during fermentation despite the presence of sufficient nutrients. PYF can cause negative impacts on beer quality and thus can be quite costly to brewers and maltsters. To investigate the causative agent of PYF, small‐scale fermentations were undertaken in both test tubes and cuvettes (15 and 3.5 mL respectively) using worts prepared from PYF‐positive and PYF‐negative malt samples. Fermentations were carried out using six malts, for up to seven days. Turbidity and extract values were monitored for all samples. The small scale (test tube) assay exhibited clear yeast cell flocculation differences between malts. In the cuvette assay the wort fermented, but the yeast cells settled out of suspension rapidly. While this property made the cuvette assay unsuitable for detecting PYF malt, it did allow for measurement of impaired sugar uptake by the yeast independent of yeast in suspension effects. All wort samples fermented in the cuvette assay showed a similar decline in apparent extract (p > 0.05), indicating that (at least in the samples studied) premature yeast flocculation was not caused by a decline in yeast activity. We believe the simple cuvette assay reported here could have application in the measurement of anti‐metabolic factors in fermenting media.     

Premature yeast flocculation factors from barley malt present in both malt husk and the non‐husk part

In the present study, small‐scale fermentations of seven malts from different maltsters in China were used to monitor their premature yeast flocculation (PYF) potential. Husk exchange was applied between PYF negative malt (PYF‐) and PYF positive malt (PYF+) to investigate the PYF factors potentially present in the husk. The results showed that PYF factors were present in both malt husk and the non‐husk part. The two factors showed various ratios among different PYF+ malts, and either of them could induce PYF if it reached the threshold. Moreover, the major antimicrobial substances damaging the yeast cells were in the non‐husk part. Copyright © 2014 The Institute of Brewing & Distilling     

The role of ferulic acid and arabinoxylan in inducing premature yeast flocculation

Premature yeast flocculation (PYF) is a universal phenomenon and has caused serious problems in the brewing industry. For brewing quality control, it is of great value to investigate the PYF factors that induce this destructive phenomenon. In the present study, two barley malts (PYF+ and PYF?), made from the same barley cultivar by one maltster in China, were selected for PYF factor investigations. The results showed that considerably higher amounts of the bound ferulic acid (FA), rather than arabinoxylan (AX), existed in the PYF+ wort compared with the PYF? wort. To better understand the role of these polysaccharides in PYF+ and PYF? wort, they were fractional precipitated with graded ethanol concentrations. The AX and FA contents in each fraction, as well as the molecular weight profiles and monosaccharide composition, were determined. Furthermore, the PYF?inducing activities of each fraction were measured using a small‐scale fermentation. It was found that the 40% ethanol‐precipitated fraction of both the PYF+ and PYF? wort, and the 60% fraction from the PYF+ wort, could induce the severe PYF phenomenon when added to the PYF? wort. These fractions were proposed to contain PYF factors of suitable molecular weight and a sufficient amount of the polysaccharides. In addition, it was found that the bound FA in arabinoxylan behaved as an important PYF factor in barley malt. The results of this work may contribute to the further study of the PYF mechanism. Copyright © 2015 The Institute of Brewing & Distilling     

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.     

Quality assessment of lager brewery yeast samples and strains using barley malt extracts with anti-yeast activity

Membrane active anti-yeast compounds, such as antimicrobial peptides and proteins, cause yeast membrane damage which is likely to affect yeast vitality and fermentation performance, parameters which are notoriously difficult to analyse. In this work the sensitivity of lager brewery yeast strains towards barley malt extracts with anti-yeast activity was assessed with an optimised assay. It was found that yeast, obtained directly from a brewery, was much more sensitive towards the malt extracts than the same yeast strain propagated in the laboratory. Sensitivity to the malt extracts increased during the course of a laboratory scale fermentation when inoculated with brewery yeast. As the assay was able to differentiate yeast samples with different histories, it shows promise as a yeast quality assay measuring the yeast's ability to withstand stress which can be equated to vitality. The assay was also able to differentiate between different lager yeast strains of Saccharomyces cerevisiae propagated in the laboratory when challenged with a number of malt extracts of varying anti-yeast activity. The assessment of yeast strains in the presence of malt extracts will lead to the identification of yeast strains with improved quality/vitality that can withstand malt-associated anti-yeast activity during brewery fermentations.     

THE MEASUREMENT OF DIMETHYL SULPHIDE PRECURSOR IN MALTS,ADJUNCTS, WORTS AND BEERS

Dimethyl sulphide in beer originates from a precursor in the malt. A method is described for the measurement of this precursor in brewing raw materials, wort and beer. The precursor levels in various green malts, kilned malts, and adjuncts are given. Excess methionine inhibits precursor uptake by yeast during fermentation. Residual precursor is still present in some commercial bottled beers.     

Current Developments in Malting and Brewing Trials with Sorghum in Nigeria: A Review

Initially, large‐scale lager beer brewing with sorghum malts proved highly intractable due to a number of biochemical problems including: high malting losses estimated at 10–30% as against 8–10% for barley; high gelatinisation temperatures which limited starch solubilisation/ hydrolysis by the amylolytic enzymes during mashing; low extract yield/low diastatic power (DP) due to inadequate hydrolytic enzyme activities especially β‐amylase; low free α‐amino nitrogen (FAN) due to inadequate proteolysis limiting yeast growth during fermentation; high wort viscosities/beer filtration problems due to low endo‐β‐1,3; 1–4‐glucanase activities on the endosperm cell walls causing the release of some β‐glucans. Strident research efforts using improved Nigerian sorghum malt varieties (SK5912, KSV8 and ICSV400) have reported some encouraging results. The knowledge of the biochemical integrity of the endo‐β‐glucanases of the sorghum malt is helping to elucidate their mode of activity in the depolymerisation of the β‐glucans. This is bound to ensure process efficiency in sorghum beer brewing, reduce beer production costs and ultimately, produce a Pilsner‐type of lager beer with 100% sorghum 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。     

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.     

Fungal Hydrophobins as Predictors of the Gushing Activity of Malt

Fungal infection of barley and malt, particularly by strains of the genus Fusarium, is known to be a direct cause of beer gushing. We have shown previously that small fungal proteins, hydrophobins, isolated from strains of the genera Fusarium, Nigrospora and Trichoderma act as gushing factors in beer. A hydrophobin concentration as low as 0.003 ppm was sufficient to induce gushing. The gushing‐inducing abilities of the isolated hydrophobins varied probably due to their structural differences. The hydrophobins did not affect beer foam stability. A correlation was observed between the hydrophobin level analyzed by the hydrophobin ELISA developed and the gushing potential of malt. The risk of gushing was found to increase with hydrophobin concentrations above 250 μg/g malt. The levels of hydrophobin and the Fusarium mycotoxin deoxynivalenol (DON) in malts were not correlated which indicated that the formation of those two fungal metabolites may not be linked. Furthermore, we did not observe a correlation between the DON content and the gushing potential of the malt studied. Our observations suggest that the accuracy of predicting gushing could be improved by measuring the amount of the actual gushing factors, hydrophobins, in barley or malt.     

Enhancing the Microbiological Stability of Malt and Beer — A Review

While beer provides a very stable microbiological environment, a few niche microorganisms are capable of growth in malt, wort and beer. Growth of mycotoxin‐producing fungi during malting, production of off‐flavours and development of turbidity in the packaged product due to the growth and metabolic activity of wild yeasts, certain lactic acid bacteria (LAB) and anaerobic Gram negative bacteria, impact negatively on beer quality. It follows that any means by which microbial contamination can be reduced or controlled would be of great economic interest to the brewing industry and would serve the public interest. There has been an increasing effort to develop novel approaches to minimal processing, such as the exploitation of inhibitory components natural to raw materials, to enhance the microbiological stability of beer. LAB species, which occur as part of the natural barley microbiota, persist during malting and mashing, and can play a positive role in the beer‐manufacturing process by their contribution to wort bioacidification or the elimination of undesirable microorganisms. Other naturally occurring components of beer that have been valued for their preservative properties are hop compounds. It may be possible to enhance the antimicrobial activities of these compounds during brewing. Some yeast strains produce and excrete extracellular toxins called zymocins, which are lethal to sensitive yeast strains. Yeast strains resistant to zymocins have been constructed. Imparting zymocinogenic activity to brewing yeast would offer a defence against wild yeasts in the brewery. Thus, the antimicrobial properties of naturally occurring components of raw materials can be exploited to enhance the microbial stability of beer.     

添加小麦芽对啤酒发酵中化学物质变化的影响

目的:通过配制不同配比的混合麦芽发酵啤酒,运用化学方法分析啤酒发酵过程中主要化学物质变化的影响来探讨混合麦芽用于啤酒发酵对啤酒品质的影响。方法:采用刚果红法、高效液相色谱法、气相色谱法等常用化学方法测定啤酒中β-葡聚糖、阿拉伯木聚糖、有机酸和挥发性物质的含量。结果:随小麦芽添加量增加啤酒中粘度升高;挥发性物质中醇类先升高后降低,酚类物质、多种有机酸的含量提高;感官评价评分在小麦添加量为50%达到最大值。结论:添加小麦芽可改变啤酒中化学成分的组成,显著提高啤酒的品质。      

Influence of barley variety and malting process on lipid content of malt

The lipid content of a beer affects its ability to form a stable head of foam and plays an important role in beer staling. The concentration and the quality of lipids in beer depend on their composition in the raw materials and on the brewing process and they may exert considerable influence on beer quality. This paper presents an investigation of the influence of barley variety and malting process on the lipid content of finished malt. Five barley samples, grown in Italy, representing 4 spring barley and 1 winter barley were used. The samples were micro-malted and analysed. The aim of this research was to verify the influence of different barley varieties on the lipid content of malt and also on the changes in fatty acid (FA) profile during the malting process. Lipid content and FA profile were evaluated. Principal component analysis (PCA) was used to establish relationships between the different samples. An evaluation of the correlation between lipid content of barleys and the quality of the resulting malts was also conducted. The data showed that the total lipid content during the malting process decreased significantly as barley was converted into malt. Different barley varieties present different FA contents and different FA patterns. The correlation between the lipid content of barley and the quality of the resulting malt confirmed the negative influence of lipids.     

Malting for Brewhouse Performance*

In many instances brewhouse performance cannot be predicted from a finished malt specification. This is particularly so for factors such as lautering, yeast performance, filtration and head character. There are two aspects involved in improving the brewing performance of malt. Firstly, an understanding of the malt characteristics affecting particular aspects of the brewing process and secondly an understanding of how the malting process affects or can be controlled to optimise these characteristics and thus their performance. In this work the relationship between barley variety, steeping pattern, malt quality and brewing performance is investigated. Six different barley varieties were micromalted in a Seeger micromalting unit under four different steeping regimes. Sub-samples were taken at intervals during steeping for enzyme analysis and measurement of water distribution. Following steeping, the samples were germinated and kilned using standard micromalting conditions. Finished malts were analysed by standard EBC methods for routine malt quality parameters including apparent attenuation limit. Worts were tested for total β-glucan content, β-glucan molecular weight distribution, filter plugging potential and carbohydrate levels. A sub set of malt samples were then micro-brewed and tested for β-glucan molecular weight (MW) distribution, beer filterability and foam stability.     

Wheat Variety and Barley Malt Properties: Influence on Haze Intensity and Foam Stability of Wheat Beer

Laboratory wheat beers were brewed with different wheat varieties of different protein content (8.7–14.4%) and with five different barley malts, varying in degree of modification (soluble protein: 3.9–6.9%). In a first series of experiments, it was investigated whether wheat positively influences the foam stability, a major characteristic of wheat beers. NIBEM and Rudin (CO₂) foam analyses revealed that the effect of wheat on foam stability depended on the barley malt used for brewing. When using malt with high foaming potential, wheat exerts a negative influence. However, wheat added to over‐modified malt with less foam promoting factors, ameliorates beer foaming characteristics proving that wheat contains foam active compounds. In addition, Rudin (N₂) values suggested that wheat positively influences foam stability by decreasing liquid drainage, probably caused by a higher beer viscosity and/or a finer foam bubble size distribution. Furthermore, the haze in wheat beers, which is another important quality characteristic of these beers, was investigated. Permanent haze readings of the 40% wheat beers were lower than 1.5 EBC haze units. For 20% wheat beers, an inverse relation between the permanent haze (9.4–19.3 EBC haze units) and the protein content of the wheat was established. The barley malt used for brewing also influenced permanent haze readings. A positive correlation between the modification degree of the malt and the permanent haze intensity was found. It was concluded that the choice of raw materials for wheat beer brewing considerably influences the visual properties of the beer.     

Fungal Hydrophobins in the Barley‐to‐Beer Chain

Fungal hydrophobins have been shown to induce gushing of beer. In order to study the occurrence and fate of hydrophobins at different stages of the production chain of beer, barley samples artificially infected in the field with Fusarium culmorum, F. graminearum and F. poae were collected during the growing period as well as during various stages of the malting process. In addition, naturally infected malt was brewed in pilot scale and samples were collected throughout the process. The samples were assayed for hydrophobin content using an ELISA method. The results showed that fungi produced hydrophobins that accumulated during barley grain development in the field, but that production was more pronounced during malting. Prolonged storage of barley tended to reduce the ability of fungi to produce hydrophobins in malting. Studies on the fate of hydrophobins during the brewing process revealed that mashing released hydrophobins from the malt into the wort. Some loss of hydrophobins occurred throughout the brewing process with spent grains, cold break (wort boiling) and surplus yeast. In addition, the beer filtration step reduced hydrophobin levels. Despite the substantial loss of hydrophobins during brewing, the level was high enough to induce the gushing detected in the final beer.     

Protein changes during malting and brewing with focus on haze and foam formation: a review

Beer is a complex mixture of over 450 constituents and, in addition, it contains macromolecules such as proteins, nucleic acids, polysaccharides, and lipids. In beer, several different protein groups, originating from barley, barley malt, and yeast, are known to influence beer quality. Some of them play a role in foam formation and mouthfeel, and others are known to form haze and have to be precipitated to guarantee haze stability, since turbidity gives a first visual impression of the quality of beer to the consumer. These proteins are derived from the malt used and are influenced, modified, and aggregated throughout the whole malting and brewing process. During malting, barley storage proteins are partially degraded by proteinases into amino acids and peptides that are critical for obtaining high-quality malt and therefore high-quality wort and beer. During mashing, proteins are solubilized and transferred into the produced wort. Throughout wort boiling proteins are glycated and coagulated being possible to separate those coagulated proteins from the wort as hot trub. In fermentation and maturation process, proteins aggregate as well, because of low pH, and can be separated. The understanding of beer protein also requires knowledge about the barley cultivar characteristics on barley/malt proteins, hordeins, protein Z, and LTP1. This review summarizes the protein composition and functions and the changes of malt proteins in beer during the malting and brewing process. Also methods for protein identification are described.     

THE CAMBRIDGE PRIZE LECTURE 1995: INDIRECT AND DIRECT CONTRIBUTIONS OF BARLEY MALT TO BREWING

The suitability of barley malt as a raw material for brewing is determined by an amalgamation of “indirect” and “direct” contributions to the beer produced. Indirect contributions are considered as those which affect the quality of the brewing process performance whereas direct contributions are considered as those which affect the quality of the product. As a potential indirect contribution of malt to brewing quality evidence is presented that barley malt contains a flocculent which influences mash filterability. As a potential direct contribution of barley malt to beer quality evidence is presented that the mineral silicate found in beer may have a role in moderating dietary aluminium.     

The influence of LOX‐less barley malt on the flavour stability of wort and beer

The aim of this study was to investigate the influence of lipoxygenase‐less (LOX‐less) barley malt on the quality of wort and beer, with the main focus on beer flavour stability. In the current study, pilot‐scale (1000 L) brewing trials were conducted with a control barley malt AC Metcalfe and a LOX‐less barley malt, PolarStar. The results clearly indicated that the LOX‐less barley malt showed less nonenal potential than the control, although LOX activities in both barley malts were relatively low. The beer brewed from the LOX‐less barley malt contained much lower concentrations of trans‐2‐nonenal (T2N) and gamma‐nonalactone, especially after the (forced or natural) aging of the beer, compared with the beer brewed under the same conditions using the control malt. The sensory panel evaluation indicated similar results in the general flavour profile. The freshness scores of beer brewed from the LOX‐less malt were higher than those from the control malt, and this was more pronounced after forced aging. In addition, the beer brewed from LOX‐less malt had a much better foam stability, almost 30 s (NIBEM test). These results confirm that the use of the LOX‐less barley malt was beneficial to beer flavour stability and foam stability. Copyright © 2014 The Institute of Brewing & Distilling     

Reduced Phytate Barley Malt to Improve Fermentation Efficiency

Brewery fermentations require continuous yeast growth to efficiently convert fermentable sugars to ethanol. Yeast growth is dependent on an adequate supply of nutrients, including minerals. Minerals are generally assured in the brewery with addition of nutrient supplements but reduced phytate barley malts could reduce the need for supplements. The present study used bulked segregant analysis to determine effects of the reduced phytate trait in barley on field performance, barley quality, malting quality and brewing performance. Two bulks from a doubled haploid population, along with a series of normal and reduced phytate controls, were grown at 3 to 5 western Canadian sites in 2006, 2007 and 2008. The normal and reduced phytate barley bulks had similar yields, but the reduced phytate barley had significantly lower test weight. Rates of endosperm modification were similar between the two phytate types, although, reduced phytate malt was significantly more friable. Malt extract and α‐amylase levels were significantly lower in the reduced phytate bulk. Zinc and magnesium levels were significantly higher in reduced phytate worts and these worts produced better yeast growth as indicated by greater amino acid use during fermentation. Brewing performance tended to be better with reduced phytate worts, but not consistently so, likely due to the lower levels of malt extract and α‐amylase. Results supported the incorporation of the reduced phytate trait into malting barley varieties, but with attention to breeding for improved test weight and levels of α‐amylase.