Antioxidant Characteristics of Hops and Hop Products

The method based on the reaction of stable DPPH radical proved to be the best for the determination of antioxidant characteristics of hops and hop products. Antioxidant activity is expressed as the rate of decline in absorbance of the reaction environment and assessed in relative percents. Differences in the values of antioxidant activity were determined in Czech and foreign hop varieties. The highest antioxidant activities in the scope of 70 to 80% rel. were measured in Saaz and Spalter Select. Antioxidant activity in most of the varieties moved in the scope of 40 to 60% rel. A part of antioxidant activity of hops is irreversibly lost in the course of drying. The loss does not usually exceed 5% of the original RA_DPPH value. Drying also resulted in a decrease of polyphenol compound contents. Drying in belt and chamber kilns is comparable from the point of view of preserving hop antioxidant properties. Results of determination of antioxidant activity in hot water extracts of raw hops and ground hops were comparable and statistically non‐significant. The same held true for pelletizing of ground hops. The antioxidant activity of raw hops declined in the course of long‐term storage in dependence on storage temperature. Storage temperature had no effect on the antioxidant activity of the hop pellets packed in a multi‐layer foil without air access.     

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     

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     

125th Anniversary Review: The Role of Hops in Brewing

Although hop technology has been a substantial part of brewing science for the last 130 years, we are still far from claiming to know everything about hops. As hops are considered primarily as a flavour ingredient for beer, with the added benefit of having anti‐microbial effects, hop research is focused on hops as a bittering agent, as an aroma contributor and as a preservative. Newer fields in hop research are directed toward the relevance of hops in flavour stability, brewing process utilisation, the technological benefits of hops in brewing as well as hops as a source of various substances with many health benefits. However the more we find out about the so‐called “spirit of beer” the more questions emerge that demand answers. While hop research was only an ancillary research field for decades, during the last ten years more universities and breweries have determined that hops must play a meaningful role in their research efforts. This article gives an overview of the up‐to‐date knowledge on hop aroma, hop derived bitterness, and the role of hops in flavour stability as well as light stability. Hop research is a wide field, therefore in this review only selected topics are reviewed. Other research areas such as hops utilisation, the antifoam potential of hops, or the advances in knowledge pertaining to the physiological valuable substances of hops go beyond the scope of this article.     

新型酒花制品在啤酒工业的应用

啤酒花是啤酒工业的重要原料之一。阐述了啤酒花中3类物质即酒花树脂、酒花油、多酚物质的主要化学成分，酒花在啤酒酿造中的作用，以及酒花浸膏和酒花油等多种新型的酒花制品在啤酒工业中的应用。     

Biologically Active Compounds from Hops and Prospects for Their Use

Although female cones of the hop plant (Humulus lupulus) are known primarily as raw material supplying characteristic bitterness and aroma to beer, their equally significant health‐promoting effects have been known to mankind for several thousand years and hop is a plant traditionally utilized in folk medicine. This paper summarizes the scientific knowledge on the effects of all 3 major groups of secondary metabolites of hops; polyphenols, essential oils, and resins. Because of their chemical diversity, it is no coincidence that these compounds exhibit a wide range of pharmacologically important properties. In addition to antioxidant, anti‐inflammatory, and anticancer‐related properties, particular attention is being paid to prenylflavonoids that occur almost exclusively in hops and are considered to be some of the most active phytoestrogens known. Hop oils and resins are well known for their sedative and other neuropharmacological properties, but in addition, these compounds exhibit antibacterial and antifungal effects. Recently, alpha bitter acids have been shown to block the development of a number of complex lifestyle diseases that are referred to by the collective name “metabolic syndrome.” Information presented in this review confirms the significant potential for the use of hops in the pharmaceutical industry and provides an understanding of beer as a natural drink that, although moderately consumed, may become a source of many health‐promoting compounds.     

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.     

酒花收获和贮藏的质量管理

酒花贮藏指数通常用来表示酒花的新鲜度,便于酿造者精确地了解酒花在采摘,加工以及贮藏过程中是否处理得当。对2003～2005年期间4个斯洛文尼亚的酒花品种和1个国外的酒花品种的延后采摘以及不同贮藏条件下酒花的新鲜度进行了测试。酒花采摘后(技术成熟)立刻采用ASBCH-6,12方法分析酒花的贮藏指数(HSI),EBC7.4方法分析酒花的α-酸。技术成熟后采摘的样品分别贮藏在0℃和20℃,并分别在1个月,2个月,3个月和6个月后进行分析。为了了解酒花在自然生理成熟期间α-酸和HSI的变化,每一品种留30株延后采摘,然后再以同样的时间间隔采摘和分析,11月底采摘最后的酒花样品。结果表明,自然生理成熟酒花的氧化进程低于酒花在20℃贮藏1个月,2个月,3个月和6个月的氧化进程。生理成熟后采摘的酒花的贮藏指数如果以A275/A325定义,则仍然具有新鲜酒花的质量。     

超临界萃取啤酒花浸膏及其萃余物中多酚化合物提取的研究

CO2啤酒花浸膏因质量稳定,易于储存和利用率高等特点在啤酒酿造中的使用量正在逐年增加。文章考察了超临界CO2萃取啤酒花浸膏的工艺对产品中啤酒花多酚含量的影响,并以超临界CO2萃取啤酒花的萃余物质为原料,研究了从中提取啤酒花多酚的可能性。结果表明,当萃取温度为40℃,萃取压力大于25MPa时,浸膏中的多酚含量明显提高,更高的提取温度得到的产品中多酚的含量没有明显的提高。采用溶剂法从萃余物质中提取啤酒花多酚的实验表明,50%(W/W)的丙酮-水的混合溶剂体系对啤酒花多酚的提取效果最好,总收率可达到83.70%(W/W),从超临界萃取啤酒花的萃余物质中提取啤酒花多酚可提高啤酒花综合利用的价值。     

PRODUCTION-SCALE APPARATUS FOR THE INJECTION OF HOP EXTRACTS INTO BEER USING LIQUID CARBON DIOXIDE

Extracts of hops made with liquid carbon dioxide can be substituted for dry hops to introduce the flavour of hop oils into beer. Apparatus has been devised so that such extracts can be redissolved in liquid carbon dioxide and then metered into beer. Successful trials have been carried out on the commercial scale.     

Hop proanthocyanidins for the fining of beer

Fining agents are used in the clarification of beers; they help to reduce the time required to sediment suspended yeast cells and ensure the clarity and colloidal stability of beer. Following an adventitious observation during dry‐hopping experiments, we identified a fining activity associated with Saaz hops. Extracts of hop cones were subsequently shown to have the capacity to flocculate yeast and result in their sedimentation. This activity has since been identified in extracts of many different hop varieties and, significantly in spent hops, the co‐product resulting from commercial extraction of hops with either CO₂ or ethanol. Here we illustrate the activity of the novel finings extracted from spent hops following CO₂ extraction of Galena hops. The sediments formed on fining were compact, relative to those obtained when commercial isinglass was used to fine the same beers. The hop extracts were also effective in reducing 90° haze in beers under conditions designed to mimic both cask ale (12 °C) and lager (4 °C) type applications. The compounds responsible for the fining activity appear to be large (30–100 kDa, or more) polyphenols. Analysis of the polyphenols using colourimetric tests indicated the presence of proanthocyanidins. On acidic hydrolysis these generated cyanidin, which would be derived from a polymer composed of catechin and epicatechin subunits. The presence of these materials in spent hops offers the possibility to develop commercial products, with desirable fining properties, from an existing co‐product stream. Furthermore, the finings are derived from a traditional ingredient of the brewing process. Copyright © 2015 The Institute of Brewing & Distilling     

PREPARATION OF HOP EXTRACTS RICH IN PARTICULAR CONSTITUENTS*

When a column containing powdered hops is extracted with liquid carbon dioxide, chromatographic separation of hop components occurs. They are extracted in the order essential oils, β-acids, α-acids; and the separation is enhanced when finely milled hops are extracted. Early fractions (～0·5 hour) contain a high proportion of the available essential oils when hops are extracted at ?20°C and such extracts are suitable as a replacement for dry hops. Fractions can be obtained from extractions at ～7°C which are rich in α-acids and contain low levels of β-acids. Small amounts of fats and waxes are normally present in fractions collected towards the end of a run when seeded hops are extracted.     

EFFECTS OF PRODUCTS FROM SEEDLESS AND SEEDED HOPS ON BEER QUALITY

Comparative semi-industrial brewing trials with standard Continental lager beers have been carried out in Switzerland using hop pellets and hop extracts made from seeded and seedless hops. It has been demonstrated that the products from seeded hops containing 8% and 9% of seeds have no adverse effect on beer quality and that the flavour of all the beers was acceptable.     

酒花制品有效成分稳定性研究

以α-酸、β-酸、总黄酮、黄腐酚含量为指标,比较了真空包装的压缩啤酒花、颗粒啤酒花、啤酒花浸膏在20℃、4℃、-20℃避光贮藏120d的成分变化.结果表明,随着温度的降低,压缩酒花、颗粒酒花、酒花浸膏中有效成分变化幅度逐渐变小,其中酒花浸膏中有效成分变化幅度最小,在20℃、4℃和-20℃贮藏条件下酒花浸膏中α-酸变化幅度分别为13.82％、7.39％、3.38％,β-酸17.13％、11.18％、6.80％,总黄酮4.48％、2.19％、1.56％,黄腐酚10.09％、5.68％、4.21％,以-20℃贮藏条件下酒花浸膏变化幅度最小.     

THE STABILITY OF HOP OILS IN LIQUID CARBON DIOXIDE EXTRACTS OF HOPS

Portions of extracts obtained by treating three varieties of hops with liquid carbon dioxide were stored in the cold and at ambient temperature for 18 months. During this period the composition of nop oils remained stable, except for the formation of two terpene methyl sulphides in extracts from all three varieties. Ales were ‘dry-hopped’ using portions of the stored extracts and, despite formation of the two sulphur compounds, the resulting hop character was satisfactory in all cases.     

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.     

EFFECT OF SULPHURING ON HOP OIL COMPOSITION

Samples of hop oil were isolated from a number of different samples of sulphured and unsulphured hops using the recommended Institute of Brewing analytical procedure. Gas chromatographic analysis of these oils using a flame photometric sulphur detector shows that sulphuring causes reduction in amount or even elimination of some of the sulphur compounds. This provides a convenient technique for determining whether or not hops have been sulphured.     

The Oxygenated Sesquiterpenoid Fraction of Hops in Relation to the Spicy Hop Character of Beer

Hop‐derived sesquiterpenoid‐type oxidation products have been associated with a spicy or herbal hoppy beer character. However, the flavour threshold values of hitherto identified oxygenated sesquiterpenes are generally much higher than their estimated levels in beer. By applying two‐step supercritical fluid extraction of hop pellets using carbon dioxide, followed by chromatographic purification of the enriched sesquiterpenoid fraction, highly specific varietal hop oil essences containing all main oxygenated sesquiterpenes were obtained. Post‐fermentation addition (at ppb levels) of these purified sesquiterpenoid essences from various European aroma hops led to distinctive spicy or herbal flavour notes, reminiscent of typical ‘noble’ hop aroma. It is concluded that a spicy hop flavour impression in beer depends significantly on minor constituents of the natural sesquiterpenoid hop oil fraction.