HOP EXTRACTS—A REVIEW

The production and use of both hop extracts and isomerized hop extracts is reviewed with particular reference to recent advances in hop extract technology.     

HOP AND MALT PHENOLICS IN LAGER BREWING

Malt tanninogens were completely removed from wort by Nylon 66 treatment and a hop phenolic extract added in amounts calculated to restore the original tanninogen level as well as the level derived only from hops. In the former case, the restoration was incomplete, which was indicative of a higher polymeric tanninogen content of hops as compared with malt, while in the latter case, the chemical interactions during kettle boiling affected the original anthocyanogen-to-catechin ratio. Physical stabilities of all the experimental brews were significantly improved in comparison with the control all-malt lager, indicating that malt tanninogens are more haze active than hop tanninogens. Hop intensity and bitterness, as well as colour, were higher in the experimental brews than in the control lager.     

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。     

ADDITION OF HOP EXTRACTS TO BEER USING LIQUID CARBON DIOXIDE*

A method is described for imparting hop character to beer using extract prepared by treating hops with liquid carbon dioxide. The long contact times required for conventional dry-hopping techniques are avoided, and the use of liquid carbon dioxide as a medium for dispersal of the extract obviates problems due to residual organic solvent or emulsion stabilizers. Beers in which hop character was introduced in this way were found to be similar in flavour to control beers treated with portions of the same hop extract dissolved in ethanol.     

啤酒花的化学成分及药理作用研究进展

啤酒花是大麻科葎草属多年生攀岩植物,其主要活性成分有以葎草酮类和蛇麻酮类为主的树脂类成分和其衍生物,黄腐酚、异黄腐酚为代表的多酚类化合物以及以萜烯类和萜烯类氧化物为主的挥发性风味成分。除酿造特性之外,近年来对啤酒花的研究已开始关注到抗肿瘤、防治骨质疏松、抑制白血病细胞的生长和抗氧化等功能。啤酒花也是传统的中药之一,有健胃、安神、化痰止咳、抗菌消炎等功效。本文综述了啤酒花的化学成分和药理作用研究进展,为其进一步的研究开发提供参考。     

STABILITY OF ESSENTIAL OIL OF HOPS

The stability of hop essential oil in beers, in hops and in aqueous emulsions has been investigated. Hop character of beers treated with hop oil emulsion has stability on pasteurization and storage similar to that of dry hopped beers. When bottled with high levels of headspace air, beers lose hop character. Beers dry-hopped with stored hops or with hops damaged during pelleting tend to develop sulphury flavours. However, hop oil emulsions prepared from such hops give rise to a sound hop character in beer. Hop oil emulsion produced by the new process shows good stability physically, chemically and biologically, particularly when mechanically homogenized and stored under an inert atmosphere. The extent of any chemical alteration due to contact with air may be estimated spectrophotometrically.     

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.     

PROTEIN PRECIPITATION DURING WORT BOILING: QUALITY ASPECTS OF DIMINISHED WORT BOILING TIMES OF BREWS PREPARED FROM PROANTHOCYANIDIN-FREE OR REGULAR RAW MATERIALS

When using proanthocyanidin-free materials for the production of beer, a reduction of the wort boiling time can be considered. In worts prepared with regular malt and tannin-free hop extract there is a continuous precipitation of the malt flavanoids while in brews prepared from proanthocyanidin-free malt and regular hops there is a simultaneous extraction and removal of the hop flavanoids leading to constant levels of these hop flavanoids. The results also show that the level of Kjeldahl nitrogen in worts boiled with hops will be the same as that in worts boiled with n-hexane tannin-free hop extracts. These results and the fact that more protein precipitates in brews containing no malt or hop proanthocyanidins suggest that, unlike what is the case during the development of beer haze, polyphenols are not necessary for an effective protein precipitation during wort boiling.     

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.     

PREPARATION OF OIL RICH HOP EXTRACTS AND THEIR ADDITION TO BEER ON THE PILOT-SCALE USING LIQUID CARBON DIOXIDE*

The introduction of carbon dioxide hop extracts dissolved in liquid carbon dioxide to green beer during transfer from fermentation vessel to cold conditioning tank results in a sound dry hop flavour in the finished product. A system has been developed for injecting a solution of extract into a beer main. Extracts which are rich in hop oils are particularly suitable for imparting hop character to beer and a liquid-liquid countercurrent procedure is described for producing extract fractions containing enhanced levels of essential oil.     

啤酒酿造中欧盟的啤酒花供应特点

基于作者在国际啤酒花种植协会的活动和研究结果以及对相关文献的回顾,对欧盟的啤酒花产业结构、生产特点和欧盟啤酒花产业在世界啤酒行业的经济地位进行了综述。论述表明,欧盟啤酒花产业结构发生了很大变化。以市场为导向的结构调整及改变更具竞争力。在2000年至2008年期间,欧盟主要啤酒花种植国家中啤酒花农场的数量大幅下降。导致几乎所有欧盟成员国农场的平均规模有所增加。为保证生产利润的最大化,啤酒花农场的专业化程度在增加,经营模式也逐渐向企业经营模式转变。     

酒花制品中异α-酸浓度的测定方法

采用分光光度法探索测定异α 酸、四氢异α 酸异构体、六氢异α 酸异构体等酒花制品中异α 酸的浓度 ,利用该方法对已知标准样品中异α 酸浓度进行检测 ,其重复性与精密度的结果表明 ,该方法的变异系数≤ 1 %,回收率在 99 8%～ 10 0 5 %之间 ;方法操作简单 ,可作为啤酒企业衡量评价异α 酸、四氢异α 酸异构体、六氢异α 酸异构体等酒花制品中异α 酸浓度的检测方法     

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。     

FLAVOUR AND HAZE STABILITY DIFFERENCES DUE TO HOP TANNINS IN ALL-MALT PILSNER BEERS BREWED WITH PROANTHOCYANIDIN-FREE MALT

All-malt Pilsner beers were brewed with proanthocyanidin-free malt (ant 13 × 13 × Rupal). Hopping was with n-hexane tannin-free hop extract with or without n-hexane extracted hop residue or with whole leaf hops. The different beers were analysed chemically and presented to an expert panel to detect possible preferences and differences in bitterness and astringency. The impact of hop proantho-cyanidins on haze formation is comparable to that of malt proanthocyanidins. No differences between the beers were found in triangular tests. Statistical analysis of the paired comparison tests showed that hop proanthocyanidins do not contribute to the bitterness of beer since beer brewed with tannin-free hop extract is slightly more bitter than beer brewed with whole leaf hops. No differences in astringency were noted between beers brewed with or without hop proanthocyanidins and it was found that the panel expressed a very slight preference for beer brewed with n-hexane hop extract over beer brewed with both n-hexane hop extract and extracted hop residue.     

STABILITY OF AQUEOUS EMULSIONS OF THE ESSENTIAL OIL OF HOPS

Hop oil emulsions prepared from different varieties of hops have been found to exhibit enhanced physical stability on the addition of blends of the emulsifiers Span 20/Tween 80 or Span 60/Tween 60. Examination of the particle size and volume distributions of an emulsion by use of a Coulter Counter was found to be an excellent method of monitoring its stability. An indication as to the relative efficiency of emulsifiers can be obtained from Coulter Counter measurements on hop oil emulsions after storage for 4 days. The use of an ultracentrifuge provies a rapid means of testing emulsion stability and hence the effectiveness of emulsion stabilizers.     

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.     

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.     

PREPARATION OF HOP EXTRACTS WITHOUT USING ORGANIC SOLVENTS

Extraction of hops with liquid carbon dioxide at ambient temperature provides an attractive means of producing hop extracts which are rich in α-acids and free from hard resins, polyphenols, pigments and residual organic solvents. The resulting yellow extracts give beer with a clean bitter flavour when they are added during wort boiling. Manufacturing costs using the process are likely to be substantially less than in a conventional hop extraction plant.     

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     

Enzymatic release of odourant polyfunctional thiols from cysteine conjugates in hop

Polyfunctional thiols are contributors to the hop varietal aroma of beer. Besides free thiols, a cysteine‐S‐conjugate has recently been shown to be an additional component of the thiol potential of hop. Such cysteine adducts investigated here in four hop cultivars and in different hop forms. Hop hydroalcoholic extracts were purified on a cation exchanger and subjected to apotryptophanase β‐lyase activity. The Cascade hop variety exhibited the highest bound 3‐sulphanylhexan‐1‐ol (grapefruit‐like) potential, while both Tomahawk and Nelson Sauvin cultivars were confirmed to be important sources of bound 3‐methyl‐2‐butene‐1‐thiol (skunky‐like), 3‐sulphanylpentan‐1‐ol and 4‐sulphanyl‐4‐methylpentan‐2‐one (box‐tree‐like). Surprisingly, hop CO₂ extracts proved to contain cysteine conjugates. Although related, the concentrations of cysteine‐bound thiols in hop are not strictly correlated to the amounts of free volatiles found in the derived beers. Copyright © 2013 The Institute of Brewing & Distilling