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.     

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.     

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     

VACUUM PACKAGING OF NEW ZEALAND HOPS

Three cultivars of New Zealand hops were packaged in two ways, vacuum and non-vacuum, and stored at two temperatures, 0°C and ambient. Over the 38 week test period the degradation of Lead Conductance Value was linear for all treatments with no difference between cultivars and no evidence of a ‘safe’ or ‘delay’ period. The degradation coefficient [Lead Conductance Value (%)/week] was highest for non-vacuum packed, ambient (?0·151), followed by non-vacuum packed refrigerated (?0·077), vacuum packed ambient (?0·039) and vacuum packed refrigerated (?0·012).     

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.     

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.     

ADDENDUM: SHORT-TERM STORAGE OF PELLETS MADE FROM SIX GROWTHS OF WYE TARGET HOPS

Pellets made from powdered Wye Target hops lost both α-acids and essential oil appreciably less rapidly than did cone hops during storage at ambient temperature for up to 2 years. Pelleting Wye Target hops is more effective than cold storage of cone hops in minimising losses of α-acids and maintaining brewing value. There are differences in the rate of loss of α-acids from pellets obtained when hops from a single growth of Wye Target hops were processed by four different processors. Cold storage of pellets from two processors resulted in a loss of just 5% of their initial α-acids after 27 months.     

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。     

NEAR INFRARED REFLECTANCE ANALYSIS OF WHOLE HOP CONES

Near infrared (NIR) reflectance spectroscopy has been evaluated for the analysis of whole hops from the 1985 and 1986 U.K. crops. Good agreement, with a correlation coefficient (r) of 0·963, was obtained between reference and NIR methods for moisture measurement. A standard error of prediction (SEP) between 0·27–0·33% was achieved over the two years. Good correlations, up to 0·949 between methods, were achieved for Lead Conductance Value (SEP 0·73%). While this accuracy is not acceptable for commercial transactions the measurement could be useful for screening purposes, for example, plant breeding or monitoring of crop ripening. Similar calibrations have been achieved for α-acids (r 0·940, SEP 0·74%) and β-acids (r 0·910, SEP 0·43%). A less accurate calibration has been developed for hop oil analysis (r 0·803, SEP 0·17 ml/100g). Since no sample preparation is required, the NIR technique provides a rapid and non-destructive method for measuring all these constituents simultaneously.     

DETERIORATION OF PELLETED HOP POWDERS DURING LONG-TERM STORAGE

During prolonged storage there is a reduction in the bittering potential of commercial samples of pellets made from either powdered Northern Brewer or Styrian Golding hops. These losses are particularly pronounced for Northern Brewer pellets stored at ambient temperature in ruptured packs. Hop pellets can also lose substantial quantities of essential oil during prolonged storage at ambient temperature and usually develop marked off-aromas. Such pellets are clearly unsuitable for dry hopping beer or for late additions to the copper. Beers brewed using pellets which have been stored warm usually have shorter shelf-lives than similar beers brewed using pellets which have been stored chilled. Changes in brewing performance can be minimized by storing hop pellets in sound packs at temperatures below 12 °C. Experience on the commercial scale has shown that whole hops stored at ambient temperature appear to lose up to 21% of their initial bittering value over a period of 18 months.     

SOLUBILITY OF HOP α- AND β-ACIDS IN LIQUID CARBON DIOXIDE*: ADDENDUM: SOLUBILITY OF PESTICIDES IN LIQUID CARBON DIOXIDE

A procedure is described for determining the solubility of hop α- and β-acids in liquid carbon dioxide. Results have shown that the optimum temperature range for the extraction of hops with liquid carbon dioxide is +5 to +10°C. A number of pesticides used by hop growers are appreciably soluble in liquid carbon dioxide.     

THE DETERMINATION OF α- AND β-ACIDS IN HOPS AND HOP PRODUCTS USING HPLC

A rapid reversed phase HPLC method for the analysis for α- and β-acids in hops and hop products is described and has been evaluated. The method uses citric acid in the eluent as a complexing agent to overcome the irreversible adsorption effects shown by some columns, thus allowing optimum eluent pH to be selected. The precision of the method for analysis of hop extract has been determined giving relative standard deviations of 1·0% and 2·1% for α- and β-acids respectively. General agreement with results obtained using a polarimetric α-acids analysis method for hop extracts and hops has been demonstrated.     

ESTIMATION OF α-, β- AND ISO-α-ACIDS IN HOPS,HOP PRODUCTS AND BEER USING HIGH PERFORMANCE LIQUID CHROMATOGRAPHY

Methods are described in which high performance liquid chromatography (HPLC) is used to estimate α-, β- and iso-α-acids in hops, hop products and beer. The chromatography relies on an isocratic elution of components from a polythene ‘cartridge’ column, and the method is calibrated with the pure substances as primary standards. Using such a column over 1000 analyses have been carried out without any significant loss in resolution or precision. The procedures are sufficiently rapid for use in commercial transactions and for quality control purposes. For hops and hop extracts coefficients of variation (%) of 2·5 and 0·8 were obtained respectively for α-acids. Values of 0·9 and 0·3 were obtained for iso-α-acids in isomerised extracts and beers respectively. For some isomerised extracts it has been observed that peaks in addition to those given by the iso-α-acids are present on the chromatogram. The current method recommended by the EBC over estimates the iso-α-acid content since these other constituents are included in the analysis.     

THE STORAGE OF YEOMAN HOPS AND PELLETISED POWDERS

Studies have shown that on extended storage of up to 90 weeks at ambient temperature pockets of Yeoman hops lose α-acids less rapidly than do the other varieties of English hops which are rich in resins. As expected the rate of loss of α-acids is further reduced when Yeoman hops are stored in the cold. Pelletised powders made from Yeoman hops show excellent storage characteristics when commercial packs are kept for 12 months either at ambient temperature or in the cold.     

COMMERCIAL BREWING AND STORAGE TRIALS WITH YEOMAN HOPS

Commercial brewing trials carried out with Yeoman hops from the 1981 crop have shown that these hops are suitable for producing both ales and lager beers. Seeded Yeoman hops show good storage characteristics and lost only 15·3% of their initial Lead Conductance Values after 44 weeks storage at ambient temperature.     

THE AROMA OF HOPS I. ORIGIN AND IDENTIFICATION OF HOP AROMA SUBSTANCES

Gas chromatography of the head space was used to follow the evolution of hop aroma under different conditions of storage. Aroma from fresh hops contains mainly myrcene, which disappears as the hops get older. Meanwhile new, more volatile substances are formed, especially by degradation of the well-known α- and β-acids; when hops are kept in closed storage the aroma therefore soon takes a composite character. When the formed volatiles are allowed to escape, the aroma of hops becomes poorer with age, to disappear almost completely in the end. Twenty-five compounds have been identified in the more volatile fraction of hop extracts.     

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.     

THE INSTITUTE OF BREWING ANALYSIS COMMITTEE THE BREWING VALUE OF OLD HOPS. RELATIONSHIPS BETWEEN ANALYSES AND FLAVOUR

Beers were brewed with old and new hops and the relationships were studied between methods for estimating α-acids, beer bitterness and beer flavour. It was concluded that the α-acid content of hops at harvest is a simple and reasonably reliable guide to the brewing value of old hops; that the beer bitterness determined analytically is a good guide to that tasted; that beers brewed with old and new hops will differ little in bitter or harsh taste if the analytical bitterness levels are similar; and that tasters can distinguish between bitterness levels of 5 E.B.C. units at values around 30 units.     

老化的颗粒酒花对啤酒发酵抗氧化能力的影响

分析老化后酒花的主要成分,研究发现在酒花老化过程中α酸和β酸发生氧化降解,前期生成异α酸,随着老化的进行,继而产生葎草灵酮(humulinone)和希鲁酮(hulupones)等衍生氧化物。酒花中的总多酚含量逐渐减少,具有抗氧化性的酚酸也发生氧化聚合,使用液相色谱检测几乎无响应峰。并测定总多酚、DPPH清除率、TRAP值、TBA值等抗氧化指标来分析老化的酒花对麦汁和啤酒的抗氧化能力影响,实验发现老化的酒花对麦汁和啤酒的抗氧化能力影响较大,尤其是风味稳定性系数SI值,波动最为明显。     

Effects of N6-Benzyladenine and Storage Temperature on Shelf-Life and Quality of Raw and Cooked Broccoli (Brassica oleracea L. var. italica)

Fresh broccoli heads were dipped in solutions containing 20 ppm N⁶-benzyladenine (BA) with 0.1% Tween-20 or water with 0.1% Tween-20 for 30 sec then stored for 5 wk at 2° and 5°C. Broccoli heads receiving BA treatments maintained higher subjective quality ratings for color, turgidity, aroma, flavor, and texture throughout the 5-wk period. Gardner color measurements and total chlorophyll were significantly higher for samples treated with BA and stored at 2°C than for controls. Samples stored at 2°C had lower shear resistance than those kept at 5°C. The content of hot water insoluble materials (fiber) was much less in broccoli heads treated with BA than in untreated heads. Maintenance of good quality by BA treatment and 2°C storage was reflected in all parameters of sensory evaluations for cooked broccoli. Loss of color and reduction of quality were observed in raw and cooked broccoli during 4 wk of storage. Evaluations of quality parameters and color measurements were greatly influenced by the turgidity factor.