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.     

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.     

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.     

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.     

EFFECT OF REDUCTION IN HOP OIL CONTENT ON RATE OF DETERIORATION OF ALPHA-ACID IN HOPS

Hops in which the essential oil content has been reduced by steam distillation under vacuum lose α-acid on storage more slowly than do untreated hops.     

THE STORAGE OF WYE TARGET HOPS: ADDENDUM: STORAGE OF FIFTEEN GROWTHS OF WYE TARGET HOPS OVER 12 MONTHS

Wye Target hops lose both α-acids and bittering potential when stored at ambient temperature. Although there is some variation in the rate that different growths lose α-acids, such losses can be substantially reduced by storing Wye Target hops in the cold.     

RAPID METHODS FOR OBTAINING ESSENTIAL OIL FROM HOPS

Sufficient essential oil for variety identification can be obtained from hops in 1 hour by steam distillation or in 10 minutes by using a novel steam extraction technique.     

THE EFFECT OF STORAGE TEMPERATURE ON THE STABILITY OF THE ALPHA-ACIDS CONTENT OF BALED HOPS

The α-acids content of baled hops (Pride of Ringwood) stored at ?20°C, ?5°C, +5°C and +22°C was monitored over a twelve month storage period. The α-acids content of the hops was found to decrease at a linear rate, i.e., by zero order kinetics, at each storage temperature. The relationship between reaction rate and storage temperature was found to accord with the predictions of classical reaction kinetics, enabling a prediction of the stability of hops stored at various temperatures to be made.     

STABILITY OF RESINS IN PELLETISED HOPS

The α-acids content and Lead Conductance Value of hop pellets, manufactured from seedless Pride of Ringwood hops grown in Australia and stored at 5°C, 20°C or 30°C, were monitored over a twelve month storage period. No decrease in α-acids content occurred during storage at 5°C, whereas at 20°C the decrease (ca. 7%) was approximately one-third that experienced for baled hops of the same variety. At both 5°C and 20°C the Lead Conductance Value decreased at approximately one-third the rate of that in baled hops. During twelve months storage at 30°C the α-acids content of the hop pellets decreased by approximately 40% and the Lead Conductance Value by 30%. The hop pellets stored at 20°C and 30°C developed rancid odours during the twelve months storage period.     

ANTIMICROBIAL ACTIVITY OF HOP OIL EMULSION

Beer spoilage organisms added to hop oil emulsion rapidly die. Thus the emulsion is not a potential source of contamination of beer. However, the antimicrobial activity of the emulsion is insufficient to retard spoilage of beer contaminated from other sources.     

影响大豆分离蛋白乳化稳定性测定的几种因素研究

采用离心法对影响大豆分离蛋白乳化稳定性的测定结果的几种因素进行了研究。通过研究得出如下结论：对乳化稳定性影响最大的是油相体积分数，然后依次是蛋白质溶液浓度、pH、离子强度、离心速度。在测定的范围内，均质速度、均质时间、水浴加热时间、加热温度和离心时间对测定结果的影响都很小。     

RECENT DEVELOPMENTS IN LOW TEMPERATURE STEAM DISTILLATION OF HOP OIL

Improved equipment for producing hop oil emulsions by steam distillation at low temperature allows easier operation. In addition, a lower operating pressure results in a more efficient and less costly extraction. Emulsions obtained from similar batches of hops using both the new and older designs of hop extractors could not be distinguished by instrumental means or by a multiple comparison taste test.     

玉米胚水酶法提油工艺机理探索

探索了玉米胚水酶法提油工艺机理，结果表明：缓冲液中蛋白质溶出量随热处理时间的延长而增加，在pH50时，溶出量最低，偏离pH5．0越远，溶出量越高。热处理时间越长，缓冲液pH越低，酶解体系中低分子量蛋白质及肽所占比例越高。     

HOP OIL CONSTITUENTS DERIVED FROM THE OXIDATION OF COLUPULONE

Several spiroacetal and furanone derivatives have been detected in the volatile oxidation products formed by heating colupulone with gaseous oxygen. This finding explains the occurrence of high levels of these compounds in hops which have undergone a prolonged period of storage.     

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.     

水蒸气蒸馏法萃提大蒜精油的工艺研究

采用水蒸气蒸馏方法提取大蒜精油，并用精炼植物油萃取收集。通过研究蒜氨酸酶酶解时间、酶解温度、蒜与水质量比、蒸馏时间、大蒜粉碎程度等因素对成品大蒜油中蒜素含量的影响，得出最佳的工艺条件是：酶解时间为3h、酶解温度为55℃、蒜与水质量比为1：4、蒸馏时间为105h、大蒜粉碎程度为蒜泥。     

榛子乳饮料加工工艺及其稳定性研究

研究以棒子为主要原料的植物蛋白饮料的加工工艺及其稳定性.着重对CMC、卡拉胶、黄原胶等单一稳定剂,单甘脂、蔗糖脂、吐温80等乳化剂及乳化稳定剂在棒子乳饮料中的稳定效果进行研究.试验表明,在棒子乳饮料中0.08%卡拉胶、0.08%瓜尔豆胶、0.1%蔗糖脂,0.15%复合稳定剂效果最佳;70℃、35 MPa的条件均质有较好的效果;采用121℃、20 min的高温高压杀菌.     

ESSENTIAL OILS OF TASMANIAN GROWN HOPS*

The hop varieties Northern Brewer, Brewers' Gold, Bullion, Cluster, Pride of Ringwood and the new variety ‘B23’ were grown in Tasmania and their essential oils analysed, primarily by combined gas chromatography/mass spectrometry. The results for those varieties previously studied were similar to the published reports, while Pride of Ringwood and B23 are reported for the first time. In particular, the selinadiene content of the six oils was examined. High levels of α- and β-selinenes were recorded in Pride of Ringwood. Mass spectral data for these two selinadienes is presented in full to facilitate future identification. An attempt is made to clarify some of the confusion in the area of sesquiterpene hydrocarbons in hops.