The effect of hopping regime,cultivar and β‐glucosidase activity on monoterpene alcohol concentrations in wort and beer

Previous studies show that the complexity of hop aroma in beer can be partly attributed to the hydrolysis of glycosidically bound monoterpene alcohols extracted from hops during the brewing process to release volatile aglycones. However, fundamental studies that examine the extraction of glycosides during brewing and their subsequent hydrolysis by yeast have not been performed. Furthermore, extraction of other hop‐derived compounds into beer shows a strong dependency on the hop cultivar being used and the point at which it is added. This study focused on the extent of glycoside extraction owing to hopping regime and cultivar, and their hydrolysis by yeast β‐glucosidase activity. Glycoside concentrations of wort made with three different hopping regimes and three cultivars were measured by the difference in volatile aglycone concentrations between samples treated with purified β‐glucosidase and untreated samples. Aglycone concentrations were measured by solid‐phase microextraction gas chromatography–mass spectrometry. Additionally, β‐glucosidase activities for 80 different yeast strains and their effect on aglycone concentration in wort were determined. Results showed that yeast have a wide range of abilities to hydrolyse glycosides with a maximum hydrolysis occurring after 3 days of fermentation regardless of yeast activity. Although it was shown that yeast are capable of glycoside hydrolysis, glycoside concentrations in wort are low and make small contributions to hop aroma. These results help explain the extent to which different brewing yeasts and hopping regimes contribute to hoppy beer aroma through the hydrolysis of non‐volatile hop‐derived compounds. Copyright © 2017 The Institute of Brewing & Distilling     

异构酒花颗粒在啤酒酿造中的应用研究

对异构酒花颗粒和普通酒花颗粒进行了对比研究。结果表明,添加异构酒花颗粒可减少苦味物质的损失,酿造出的啤酒优于只采用普通酒花颗粒酿造出的啤酒,特别是酒花香突出,泡特性好。     

Impact of Different Hop Compounds on the Overfoaming Volume of Beer Caused by Primary Gushing

When weather conditions favour the growth of moulds on barley, beers brewed from the resulting malts often tend to gush. Certain Fusarium species (e.g., F. graminearum and F. culmorum) may cause this problem. Supersaturated with CO₂, a primary gushing beer contains an overcritical concentration of microbubbles; these are reputed to be stabilised by Fusarium‐derived hydrophobins. Research with varying brewhouse parameters has been performed to investigate the factors of primary gushing. As hops are known to contribute to a wide range of both gushing positive and negative substances in beer, the hopping regime has emerged as an important aspect. This paper examines the impact of different hop varieties on gushing. Hop oils and unsaturated fatty acids are reputed to be gushing‐suppressors. Compounds such as dehydrated humulinic acid can intensify the effect. Hop pellets, with a prevalent range of conductometric values (5–10% α‐acid), commonly employed in breweries to adjust bitterness and aroma were selected. By working with the same “gushing malt”, the spectrum of compounds in the finished beer only differed through the hop product used. The overfoaming volumes of different samples were determined according to MEBAK guidelines. Respective hop oil and fatty acid concentrations (by GC) and iso‐α‐acid contents (by HPLC) were compared and a chronological sequence of the changing percentages of beer loss is shown.     

Influence of hop harvest date of the ‘Mandarina Bavaria’ hop variety on the sensory evaluation of dry‐hopped top‐fermented beer

To impart a special hop aroma to beer, dry‐hopping is a technique that is becoming more and more popular with commercial breweries. Nevertheless, until now little was known about the factors that influence the reproducibility (and consistent product quality) of dry‐hopping with flavour varieties. One factor that could influence the sensory impressions and aroma profile compositions of dry‐hopped beers is the hop harvest date. Therefore, to determine the effects of different harvest dates of the flavour variety ‘Mandarina Bavaria’ on the aroma of top‐fermented beer, laboratory‐scale dry‐hopping trials were performed. Besides tasting sessions of brewed beers, relative quantities of selected hop‐derived, as well as beer‐originated aroma compounds, were investigated by headspace–solid‐phase microextraction–gas chromatography–mass spectrometry. Duo–trio tests between the beers hopped with pellets of different harvest dates showed no significant differences (α = 0.05) between them. In addition, these beers had similar profiles in a five‐point profile tasting scheme. On the other hand, relative concentrations of some hop‐derived aroma compounds – especially myrcene, which is known to be able to contribute to beer flavour – increased corresponding to a later harvest date, while beer originated volatiles were not different between the beers. Analytical results combined with the results of sensory evaluations led to the conclusion that the harvest date of Mandarina Bavaria was not a dominant factor in the dry‐hopping aroma of top‐fermented beers. High amounts of fermentation by‐products are likely responsible for masking effects resulting in no sensory distinctness between the samples with different hop aroma compound concentrations. Copyright © 2016 The Institute of Brewing & Distilling     

Humulus lupulus – a story that begs to be told. A review

The hop cones of the female plant of the common hop species Humulus lupulus L. are grown almost exclusively for the brewing industry. Only the cones of the female plants are able to secrete the fine yellow resinous powder (i.e. lupulin glands). It is in these lupulin glands that the main brewing principles of hops, the resins and essential oils, are synthesized and accumulated. Hops are of interest to the brewer since they impart the typical bitter taste and aroma to beer and are responsible for the perceived hop character. In addition to the comfortable bitterness and the refreshing hoppy aroma delivered by hops, the hop acids also contribute to the overall microbial stability of beer. Another benefit of the hop resins is that they help enhance and stabilize beer foam and promote foam lacing. In an attempt to understand these contributions, the very complex nature of the chemical composition of hops is reviewed. First, a general overview of the hop chemistry and nomenclature is presented. Then, the different hop resins found in the lupulin glands of the hop cones are discussed in detail. The major hop bitter acids (α‐ and β‐acids) and the latest findings on the absolute configuration of the cis and trans iso‐α‐acids are discussed. Special attention is given to the hard resins; the known δ‐resin is reviewed and the ε‐resin is introduced. Recent data on the bittering potential and the antimicrobial properties of both hard resin fractions are disclosed. Attention is also given to the numerous essential oil constituents as well as their contributions to beer aroma. In addition to the aroma contribution of the well‐known essential oil compounds, a number of recently identified sulfur compounds and their impact on beer aroma are reviewed. The hop polyphenols and their potential health benefits are also addressed. Subsequently, the importance of hops in brewing is examined and the contributions of hops to beer quality are explained. Finally, the beer and hop market of the last century, as well as the new trends in brewing, are discussed in detail. Hop research is an ever growing field of central importance to the brewing industry, even in areas that are not traditionally associated with hops and brewing. This article attempts to give a general overview of the different areas of hop research while assessing the latest advances in hop science and their impact on brewing. Copyright © 2014 The Institute of Brewing & Distilling     

Relationship of iso‐α‐acid content and endogenous antioxidative potential during storage of lager beer

One of the critical issues regarding the quality of beer is the change in its chemical composition that occurs during storage. Decomposition of iso‐α‐acids results in an undesirable decrease in bitterness as well as a deterioration in the sensory profile of the beer. These changes are caused by the susceptibility of iso‐α‐acids to degradation owing to the influence of reactive oxygen species and light. The aim of this study was to investigate the influence of storage conditions (temperature, light) on the degradation of iso‐α‐acids during aging, with the main focus on monitoring the relationship between the turnover of iso‐α‐acids, the sulphur dioxide content and the antioxidative potential of stored beer as measured by electron spin resonance spectroscopy. In agreement with previous investigations, a significant decrease in the content of bitter compounds (up to 18 % relative to the original level, depending on storage conditions) was observed. A significant decrease in the antioxidant potential of beer was recorded simultaneously and the data confirmed a strong correlation between these parameters. The decline in beer bitterness could become a marker for estimating oxidative damage during storage. Copyright © 2014 The Institute of Brewing & Distilling     

Assessment of changes in hop resins and polyphenols during long‐term storage

Changes in the content and composition of hop secondary metabolites during storage are reflected in beer quality and in the economics of beer production. A 12‐month storage experiment with T90 pellets of four hop varieties showed different dynamics of hop aging in relation to both storage conditions and hop variety. Negligible effects on the α‐ and β‐acids were detected during storage without air access at +2°C. Storage at +20°C resulted in a final loss of 20–25% α‐acids, but the content of β‐acids did not change significantly. Large decreases in α‐acids (64–88%) and in β‐acids (51–83%) were found in hops stored with access to air at +20°C. The rate of decline accelerated markedly after 6 months of storage. In terms of hop resin changes, Premiant and Sládek were the most and the least stable varieties, respectively. After 12 months, the content of the total polyphenols and flavonoids decreased by 30–40% and by 20–30%, respectively, irrespective of storage conditions. The rate of decline accelerated strongly after 6 months. The DPPH (1,1‐diphenyl‐2‐picrylhydrazyl) antiradical potential decrease was significant only in hops stored under aerobic conditions. The depletion was 9–25% after 1 year; Saaz was the most stable variety. Copyright © 2012 The Institute of Brewing & Distilling     

The Impact of a Xanthohumol‐Enriched Hop Product on the Behavior of Xanthohumol and Isoxanthohumol in Pale and Dark Beers: A Pilot Scale Approach

Based on the health‐promoting properties of xanthohumol (XN), the production of an enriched beer in this substance would be of interest to the brewing industry, from the perspective of pointing out the benefits that beer could bring consumer health. For that purpose, in this work efforts were applied to produce a beer enriched in XN. Also investigated was the influence of a XN‐enriched hop product on the content of XN and isoxanthohumol (IXN) in pale and dark beers. It was verified that XN was largely converted into IXN during wort boiling. However, the use of dark malts revealed a positive effect on the thermal isomerisation of XN. These results are indicative of the isomerisation‐inhibiting effect of the stout production process, which resulted in high levels of XN in the beer. Further losses of XN were due to incomplete extraction from the hops into the wort, adsorption to insoluble malt proteins and adsorption to yeast cells during fermentation. It was possible to produce a dark beer enriched in XN (3.5 mg/L) by using coloured malt (caramel malt, roasted malt and roasted malt extract) and a special XN hop extract combined with late hop usage during wort boiling.     

Behaviour of Antioxidants Derived from Hops During Wort Boiling

The oxidative stability of wort at different stages during wort production and the radical scavenging characteristics of α‐, β‐, iso‐α‐acids and a hop polyphenol extract were evaluated using ESR spectroscopy and DPPH• radical quenching measurements. Radical generation in unhopped wort was significantly, positively correlated with heating rate prior to boiling but not with dissolved oxygen content. Hop α‐ and β‐acids showed similarly significant radical quenching abilities, while iso‐α‐acids and a hop polyphenol extract displayed a negligible effect. Isomerization of α‐acids to iso‐α‐acids reduced wort's antioxidative capacity. Commercially available hop products with varying polyphenol content showed similar radical inhibiting properties, which were a function of hop acid content. Relative to an unhopped treatment, hop additions to wort resulted in significantly lower amounts of Strecker aldehydes in stored beer.     

A Review of Hop Resistance in Beer Spoilage Lactic Acid Bacteria

Hop bitter acids play a major role in enhancing the microbiological stability of beer. However, beer spoilage lactic acid bacteria (LAB) are able to grow in beer by exhibiting strong hop resistance. Recently two hop resistance genes, horA and horC, have been identified in beer spoilage Lactobacillus brevis ABBC45. The horA gene was shown to encode an ATP dependent multidrug transporter that extrudes hop bitter acids out of bacterial cells. In contrast, the product of the horC gene confers hop resistance by presumably acting as a proton motive force (PMF)‐dependent multidrug transporter. Strikingly, the homologs of horA and horC genes were found to be widely and almost exclusively distributed in various species of beer spoilage LAB strains, indicating these two hop resistance genes are excellent species‐independent genetic markers for differentiating the beer spoilage ability of LAB. Furthermore the nucleotide sequence analysis of horA and horC homologs revealed that both genes are essentially identical among distinct beer spoilage species, indicating horA and horC have been acquired by beer spoilage LAB through horizontal gene transfer. Taken collectively, these insights provide a basis for applying horA and horC to the species‐independent determination of beer spoilage LAB, including yet uncharacterized species. In addition to the hop resistance mechanisms mediated by multidrug transporters, proton translocating ATPase and the ATP production system were shown to contribute to the hop resistance mechanisms in beer spoilage LAB by generating PMF and ATP that are necessary for survival in beer.     

Screening for new brewing yeasts in the non‐Saccharomyces sector with Torulaspora delbrueckii as model

This study describes a screening system for future brewing yeasts focusing on non‐Saccharomyces yeasts. The aim was to find new yeast strains that can ferment beer wort into a respectable beer. Ten Torulaspora delbrueckii strains were put through the screening system, which included sugar utilization tests, hop resistance tests, ethanol resistance tests, polymerase chain reaction fingerprinting, propagation tests, amino acid catabolism and anabolism, phenolic off‐flavour tests and trial fermentations. Trial fermentations were analysed for extract reduction, pH drop, yeast concentration in bulk fluid and fermentation by‐products. All investigated strains were able to partly ferment wort sugars and showed high tolerance to hop compounds and ethanol. One of the investigated yeast strains fermented all the wort sugars and produced a respectable fruity flavour and a beer of average ethanol content with a high volatile flavour compound concentration. Two other strains could possibly be used for pre‐fermentation as a bio‐flavouring agent for beers that have been post‐fermented by Saccharomyces strains as a consequence of their low sugar utilization but good flavour‐forming properties. Copyright © 2015 John Wiley & Sons, Ltd.     

Pediococcus damnosus strains isolated from a brewery environment carry the horA gene

Beer is recognized as a safe beverage, owing to its excellent microbiological stability provided by its components, especially iso‐α‐acids from hop and ethanol which have antimicrobial activity. Despite these unfavourable conditions for bacteria, some lactic acid bacteria (LAB) can cause beer spoilage. Resistance to hop compounds is caused, in part, by the product of genes like horA . Understanding how LAB adapts to hop compounds as well as quick detection of these microorganisms is necessary to ensure high‐quality beverages produced by the brewing industry. In this work, we searched for the presence of two main hop‐resistance genes, horA and ORF5, and determined the capacity of four strains of Pediococcus damnosus isolated from a brewery environment to grow in the presence of increasing concentrations of iso‐α‐acids. All strains were able to grow in increasing concentrations of iso‐α‐acids up to 150 μg mL⁻¹. This amount is 10 times greater than the concentration in average beer. Genetic amplification of genes associated with hop‐resistance, demonstrated the presence of horA , but not ORF5 in all tested strains. This communication represents the first report of the presence of horA gene in bacteria isolated from breweries in our country. Copyright © 2017 The Institute of Brewing & Distilling     

FATTY ACIDS IN ISOMERIZED HOP EXTRACTS AND GUSHING

A procedure is described for the analysis of fatty acids (C₁₂-C₁₈ individually and C₁₈₊ as a group) in hops, hop extracts and isomerized hop extracts, and analytical results are quoted for twenty-one different samples of hops or hop products. Isomerized extracts varied widely in their content of fatty acids and isomerization and processing of hops appeared to eliminate some fatty acids selectively so that isomerized extracts were enriched in palmitic acid, linoleic acid and linolenic acid. Some hop extracts had a surprisingly high content of lauric acid. The analytical results are discussed in relation to gushing.     

The impact of different hop compounds on the growth of selected beer spoilage bacteria in beer

Beer spoiling lactic acid bacteria are a major reason for quality complaints in breweries around the world. Spoilage by a variety of these bacteria can result in haze, sediment, slime, off-flavours and acidity. As these bacteria occur frequently in the brewing environment, using certain hop products that inhibit the growth of these spoilers could be a solution to prevent problems. To investigate the impact of seven different hop compounds (α-acids, iso-α-acids, tetrahydro-iso-α-acids, rho-iso-α-acids, xanthohumol, iso-xanthohumol and humulinones) on the growth of six major beer spoilage bacteria (Lactobacillus brevis. L. backi, L. coryniformis, L. lindneri, L. buchneri, Pediococcus damnosous), two concentrations (10 and 25 mg/L) of each hop substance were added to unhopped beer. The potential growth of the spoilage bacteria was investigated over 56 consecutive days. A comparison of the results shows a strong inhibition of growth of all spoilage bacteria at 25 mg/L of tetrahydro-iso-α-acids closely followed by α-acids as the second most inhibitory substance. The results showed a high resistance of L. brevis to all hop compounds as well as an inhibition of L. coryniformis and L. buchneri at low concentrations of most hop components. In comparison with the control sample, L. lindneri showed increased growth in the presence of some hop compounds (rho-iso-α-acids, xanthohumol, iso-xanthohumol, humulinones). © 2020 The Authors. Journal of the Institute of Brewing published by John Wiley & Sons Ltd on behalf of The Institute of Brewing & Distilling     

Application of Plackett–Burman experimental design for investigating the effect of wort amino acids on flavour‐active compounds production during lager yeast fermentation

Aroma‐active higher alcohols and esters are produced intracellularly in the cytosol by fermenting lager yeast cells, which are of major industrial interest because they determine aroma and taste characteristics of the fermented beer. Wort amino acid composition and their utilization by yeast during brewer's wort fermentation influence both the yeast fermentation performance and the flavour profile of the finished product. To better understand the relationship between the yeast cell and wort amino acid composition, Plackett–Burman screening design was applied to measure the changes in nitrogen composition associated with yeast amino acids uptake and flavour formation during fermentation. Here, using an industrial lager brewing strain of Saccharomyces pastorianus , we investigated the effect of amino acid composition on the accumulation of higher alcohols and volatile esters. The objective of this study was to identify the significant amino acids involved in the flavour production during beer fermentation. Our results showed that even though different flavour substances were produced with different amino acid composition in the fermentation experiments, the discrepancies were not related to the total amount of amino acids in the synthetic medium. The most significant effect on higher alcohol production was exercised by the content of glutamic acid, aromatic amino acids and branch chain amino acids. Leucine, valine, glutamic acid, phenylalanine, serine and lysine were identified as important determinants for the formation of esters. The future applications of this information could drastically improve the current regime of selecting malt and adjunct or their formula with desired amino acids in wort. Copyright © 2017 The Institute of Brewing & Distilling     

啤酒酿造过程中萜烯醇类化合物变化规律

采用基于顶空固相微萃取-气相色谱质谱技术(HS-SPME/GC-MS)建立的啤酒中酒花物质的检测方法,跟踪了啤酒酿造过程中源自酒花的5种萜烯醇类香气化合物的变化规律,初步为啤酒厂酒花配方及工艺调整奠定了理论基础。通过对糖化过程中不同酒花配方、不同煮沸方式及酒花添加工艺对冷麦汁中萜烯醇类化合物含量影响的研究,发现冷麦汁中的萜烯醇类化合物主要受最后一次添加酒花的添加量和添加时机影响,最后一次酒花在煮终回旋前添加较煮终前10 min添加,更利于萜烯醇类化合物在冷麦汁中的保留,这与国外的late-hopping工艺相一致;与煮终前10 min最后一次添加相比,在煮终回旋前最后一次添加酒花能使冷麦汁中里那醇含量提高209.4%,α-萜品醇为91.2%,香叶醇为31.4%,橙花醇175.0%。通过研究发酵过程中萜烯醇类化合物的变化规律,发现5种萜烯在发酵过程中呈上升趋势,且它们之间可能被酵母相互转化。     

国产高α-酸含量酒花的品质研究

以青岛大花作为对照,研究了高α-酸含量酒花品种马可波罗(Marco Polo)和哥伦布(Columbus)的品质和酿造特点,评价高α-酸含量酒花对青岛大花的替代性。结果表明:马可波罗和哥伦布酒花的α-酸含量高,可降低酒花添加量。合葎草酮含量低,苦感柔和。酒花油组分中里那醇和香叶醇含量高,对啤酒的香气贡献大。总多酚及黄腐酚含量较高,但单位α-酸添加的多酚量不足且抗氧化能力略差,可能对啤酒的非生物稳定性、抗氧化性产生影响。从酿造麦汁指标来看,高α-酸含量酒花的使用可达到预期的苦味质,且异构化率高于青岛大花。采用高α-酸含量酒花配合多酚颗粒酒花使用可以改善麦汁的非生物稳定性和抗氧化能力。     

CAMBRIDGE PRIZE LECTURE. STUDIES ON THE SENSITIVITY OF LACTIC ACID BACTERIA TO HOP BITTER ACIDS

Hop bitter acids act as mobile-carrier ionophores. They inhibit the growth of beer-spoilage bacteria by dissipating the transmembrane pH gradient. Their activity is pH dependent. Low pH favours antibacterial activity but high pH reduces it. Resistance to hop bitter acids is a stable character, associated only with beer-spoilage lactic acid bacteria. Hop-resistant organisms can maintain a larger transmembrane pH gradient and ATP pool than can hop-sensitive organisms. Prior exposure of bacteria to trans-isohumulone does not influence the degree of resistance to hop bitter acids. However, in some strains, exposure to trans-isohumulone does induce the ability to spoil beer. The chemistry of these compounds is more complex than previously thought. In aqueous solutions, such as beer, hop acids bind to metal ions and may be covalently hydrated.