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.     

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.     

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.     

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.     

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.     

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。     

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.     

INSTITUTE OF BREWING HOPS ADVISORY COMMITTEE BREWING TRIALS WITH WYE CHALLENGER,WYE TARGET AND NORTHERN BREWER HOPS

The Wye Challenger hops brewed in the 1972 trial had higher α-acid contents but produced similar bitterness (EBU's) when brewed at similar α-acid-into-brew rates as Northern Brewer hops. On average the Wye Challenger hopped beers drunk slightly less bitter than the Northern Brewer hopped beers but, overall, drinkers indicated no preference between these beers. The Wye Target hops used in the 1972 trial came from four growths of varying α-acid contents. However, at similar α-acid-into-brew rates as used for Northern Brewer hops similar levels of bitterness (EBU's) were obtained. On average, the drinkers thought the Wye Target hopped beers drank slightly less bitter but were equally preferred on general flavour grounds to the Northern Brewer hopped beers. All breweries thought Wye Challenger, Wye Target and Northern Brewer suitable as a copper hop for at least up to 50% of the hop grist.     

THE ESSENTIAL OIL OF HOPS A REVIEW

The composition of essential oil of hops is reviewed and the nature of hop oil components which survive into wort and beer is discussed. Methods which are available to the brewer for imparting hop character to beer are critically evaluated.     

A Study of the Fate of Volatile Hop Constituents in Beer

SUMMARY— The volatile material from a pilot plant brewed beer (hopped) has been analyzed by the direct combination of capillary gas chromatography and mass spectrometry. None of the major volatile terpenoid hydrocarbons of hops (myrcene, caryophyllene, humulene) could be detected in the beer volatiles. The only volatile constituents in the beer which could be assigned to hops with some certainty were ethyl dec-4-enoate and ethyl deca-4,9-dienoate, which exist in the hop oil as the methyl esters.
A capillary gas chromatography analysis of a beer which was brewed without hops but with methyl dec-4-enoate (0.02 g/L) showed that this ester was converted to the ethyl ester by the fermentation.
A study was also carried out using model systems to parallel the "kettle boiling" step of brewing. This involved boiling hops with water for a set period and filtering the water extract from the hops. It was found that the pattern of volatile hop constituents in the filtrate (hopped water) was quite different from hop oil and consisted principally of free organic acids, humulene epoxide, humulenol, and other hop oil oxygenated components. With fine filteration through Celite, very little myrcene, humulene, or caryophyllene were transferred into the water, even though they form the major part of hop volatiles. If, however, only coarse filtration was used, a greater amount of these hydrocarbons were found in the filtrate.
It is concluded that the amount of volatile hop oil constituents reaching the final beer probably depends upon the exact conditions of the brewing process used. No evidence could be found in the present work to support the view that the tiny amounts that do survive in beer prepared by the typical American process could contribute more than a very minor amount to the characteristic beer aroma.     

DIFFERENCES IN UTILISATION OF THE ESSENTIAL OIL OF HOPS DURING THE PRODUCTION OF DRY-HOPPED AND LATE-HOPPED BEERS

Late-hopped and dry-hopped beers were prepared and their lipophilic constituents extracted using Amberlite XAD-2 resin. Examination of the volatile constituents by GC-MS confirmed that most of the hop oil added towards the end of wort boiling is lost by evaporation. Part of the material which survives boiling is chemically transformed by yeast during fermentation. Dry-hopped beer contained compounds more representative of the original hop oil than did the corresponding late-hopped beer. A liquid carbon dioxide extract of hops, rich in essential oil, has been fractionated by column chromatography on alumina-silica giving preparations which simulate either late-hop or dry-hop character.     

香型酒花对啤酒酿造质量的影响

啤酒花有两种基本类型:苦型和香型酒花.它赋予啤酒特有的苦味和香味,同时也影响啤酒的泡沫形成;酒花中含有酒花树脂、酒花油和多酚物质.本文主要就香型酒花在啤酒酿造过程中的风味变化以及对啤酒香味质量的影响进行了讨论.     

THE EFFECT OF HOP SUBSTANCES ON THE PRODUCTION OF FUSEL OIL

Unhopped beers contain more fusel oils than the corresponding normally hopped beers when certain strains of yeasts are used during fermentation. Water soluble fractions of hops and some soft resin constituents can influence fusel oil production. When hops are completely replaced by isomerized hop extracts the use of some additional hop fraction in the copper leads to the resulting beer having a similar fusel oil content to one hopped in the usual way. Partially hopped beers (0·25 lb./brl.) usually have similar fusel oil contents to beers produced using the normal quantity of hops (1·0 lb./brl.).     

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     

HOP INDUSTRY ADVISORY COMMITTEE: BREWING TRIALS WITH WYE TARGET AND NORTHERN BREWER HOPS

Brewing trials with hops from the 1974 crop complete a three-year series in which Wye Target hops have been compared for brewing suitability with a control growth of Northern Brewer hops. Between 8 and 11 breweries took part each year. Physical examination of the hops used showed Wye Target to have less seed and to have a smaller cone size than the Northern Brewer but with a tendency to be loosely packed. When brewed at similar α-acid-into-brew rates as Northern Brewer hops, beers of similar analytical and flavour-assessed bitterness were produced. On general flavour grounds the beers were equally preferred. In all cases the Wye Target hops were rated as a copper hop either as equally suitable as, or more suitable than, the Northern Brewer hops.     

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.     

THE STORAGE OF PELLETED POWDERS MADE FROM WYE NORTHDOWN HOPS

Pelleted hop powder from seeded Wye Northdown hops of the 1976 crop shows small losses in lead conductance value (LCV) when stored in commercial packs for ca. 12 months after processing. The losses for hop pellets stored at ambient temperature are slightly more rapid than for those stored at 0 to 4°C. Losses in LCV of pellets during storage in the cold or at ambient temperature are substantially less than those of seeded Wye Northdown cone hops stored in pockets under comparable conditions. The hop pellets showed no significant loss in oil content or bittering potential over the storage period. Taste panels were unable to detect differences in flavour when comparisons were made of beers bittered with pellets stored in the cold and at ambient temperature.     

PAPER STRIP ANALYSIS OF SUBSTANCES DERIVED FROM HOPS

Reasonably satisfactory methods exist for the analysis of α acids in hops. The analysis of iso α acids in beer is not so well developed. The same determinations for hop extracts and isomerized hop extracts are much more difficult. A new method for these determinations is now described. It is based on a chromatographic technique using buffered paper strips and is applicable not only to hop extracts, isomerized or not, but also to hops and to beer. The percentage of α acids and iso α acids can be determined in one analysis. Eventually the determination of humulinic aci ds β acids and hulupones will also be possible. After separating these substances from one another their amounts are determined spectrophotometrically. The method is very fast and is more accurate than any other known method.     

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.