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.     

STUDIES ON THE EFFECT OF POLLINATION ON THE YIELD AND RESIN CONTENT OF HOPS (HUMULUS LUPULUS L.)

Pollination trials in otherwise male-free hop gardens are described. The results showed that a reduction in cone yield of up to 30% may be expected from seedless hops, but an increase in α-acid content of the cones more or less compensates for this yield reduction and the yield of α-acid per acre can be almost as high from seedless as seeded hops. Northern Brewer, in particular, performed better than other varieties when grown seedless but most of the high α-acid varieties gave reasonable results. It is suggested that the variation in response may depend on the number of resin glands present on the seeds of the different varieties, and differences in the distribution of resin glands on other parts of the cone.     

KINETICS OF HOP STORAGE

After an initial ‘delay period’ the storage losses of α- and β-acids follow a first-order rate equation and not a zero-order equation as has been suggested by others.     

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).     

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.     

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 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.     

ANALYSIS OF HOPS OF THE 1987 CROP

Analytical values for α-acid content, as measured by lead conductance value, of twelve varieties of hops from the 1987 crop are presented in relation to the district of production. Satisfactory variabilities have been achieved by Fuggle, Progress, Bramling Cross, Northern Brewer, Zenith, Wye Challenger and Omega. Wye Northdown has increased in variability, reaching the upper limit of acceptability despite an increase in sampling rate. Goldings, W.G.V. and Wye Target have continued to show higher than normal variabilities. This year Yeoman has moved in variability above the acceptable limit. The sampling rates have been considered and in view of the unusual growing conditions experienced with the 1987 crop, with hop yields considerably reduced and α-acids increased to very high levels, no changes have been recommended.     

ANALYSIS OF HOPS OF THE 1985 CROP

Analytical values for α-acid content of twelve varieties of hops from the 1985 crop are presented in relation to the district of production. With the exception of the varieties Zenith, Wye Target and Yeoman, the variability of the crop gave a similar trend to that of previous years. The sampling rates have been considered and increases in the rates for Wye Target and Yeoman have been recommended.     

INSTITUTE OF BREWING HOPS ADVISORY COMMITTEE ANALYSIS OF HOPS OF THE 1972 CROP

Analytical values for 14 varieties of hops from the 1972 crop are presented in relation to the district of production. The tendency noted in 1971 for the variation within growths to diminish was continued in 1972. It was found that for Keyworth's Mid-season a sampling rate of 1 in 20 would be acceptable for commercial purposes.     

ANALYSIS OF HOPS OF THE 1986 CROP

Analytical values for α-acid content of twelve varieties of hops from the 1986 crop are presented in relation to the district of production. The variabilities of Wye Northdown, Zenith and Wye Challenger follow similar trends to those of previous years, while Northern Brewer has continued to show a reduction in variability. Following the increase in sampling rate, Yeoman has reverted to an acceptable level of variation. Fuggle, Progress and Bramling Cross have increased their variabilities but remain within acceptable limits. The variabilities of Goldings, W.G.V. and Wye Target, despite the increase in sampling rate of the latter, have attained higher than normal levels. The sampling rates have been considered and in view of the adverse growing conditions encountered with the 1986 crop, no changes have been recommended.     

HOP INDUSTRY COMMITTEE: ANALYSIS OF HOPS OF THE 1977 CROP

Analytical values for α-acid content of thirteen varieties of hops from the 1977 crop are presented in relation to the district of production. For all varieties the tolerance aim of ±0.5% was easily achieved, the whole crop being less variable than in any previous year since these records were kept. The results are acceptable for commercial purposes. α-Acid values for seedless hops from Hampshire and from the Seedless Hop Trials are included and comparisons with seeded hops are shown over a three year period.     

HOP INDUSTRY COMMITTEE ANALYSIS OF HOPS OF THE 1984 CROP

Analytical values for α-acid content of thirteen varieties of hops from the 1984 crop are presented in relation to the district of production. For all varieties, except Yeoman, the tolerance aim of ±0·5% was achieved. The production of Yeoman has almost doubled this year and the inclusion of young hops with mature hops in some growths has led to increased within growth variation and failure of this variety, by a small margin, to remain within the limits of the tolerance aim. Apart from this, the variability of the crop compared well with previous years and the results are acceptable for commercial purposes. The sampling rates have been considered and no changes have been recommended.     

HOP INDUSTRY COMMITTEE ANALYSIS OF HOPS OF THE 1982 CROP

Analytical values for α-acid content of fourteen varieties of hops from the 1982 crop are presented in relation to the district of production. For all varieties the tolerance aim of ± 0.5% was achieved this year and variability of the crop was generally the same as the average for the last five years. As before, the results are acceptable for commercial purposes. The sampling rates have been considered with no change recommended.     

HOP INDUSTRY COMMITTEE ANALYSIS OF HOPS OF THE 1981 CROP

Analytical values for α-acid content of thirteen varieties of hops from the 1981 crop are presented in relation to the district of production. For all varieties the tolerance aim of ±0·5% was achieved this year and variability of the crop was generally the same as the average for the last five years. As before, the results are acceptable for commercial purposes. The sampling rates have been considered and reductions in the rates for Keyworth's Midseason and Wye Challenger are justified.     

HOP INDUSTRY COMMITTEE: ANALYSIS OF HOPS OF THE 1978 CROP

Analytical values for α-acid content of thirteen varieties of hops from the 1978 Crop are presented in relation to the district of production. For all varieties the tolerance aim of ±0.5% was achieved and this year the crop was no more variable than the average for the last five years. As before the results are acceptable for commercial purposes.     

THE EFFECT OF TIME OF DRESSING ON THE FLOWERING BEHAVIOUR AND YIELD OF HOPS VARIETY LATE CLUSTER

The Late Cluster variety of hops when introduced to Kashmir (India) from USA gave two flowering flushes in a growing season, thus giving two harvests. By adjusting the date of dressing (root pruning) from December to May 15 the abnormal flowering behaviour of the plant could be altered from two flushes to only one. Plants dressed late in spring, April 15 to May 1, gave the highest cone yield which was expressed in only one harvest. This also produced the highest α-acids content.     

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.     

ENZYMIC DEGRADATION OF α-ACIDS IN HOPS

Evidence is presented for the biological oxidation of α-acids in hop cones by an enzyme having molecular weight 17,000 daltons, K_m 6–0 and Mn as the active metal ion. The enzyme is located in bracts and bracteoles and not in lupulin glands. The presence of an endogenous inhibitor was demonstrated. The specific activity of protein in hop cones increased with maturity and this was probably associated with release of α-acids from lupulin glands.     

HOP INDUSTRY ADVISORY COMMITTEE: ANALYSIS OF HOPS OF THE 1975 CROP

Analytical values for α-acid content of eleven varieties of hops from the 1975 crop are presented in relation to the district of production. For most of the varieties the variation within growths was lower than in the previous year. With amended sampling rates, the tolerance limits of ±0·5 % were achieved for all hop varieties and the results are acceptable for commercial purposes. Some α-acid values for seedless hops from the Seedless Hop Trials are included in the Report and comparisons with seeded hops are shown over a three year period.