PROCESS ASPECTS OF THE EXTRACTION OF HOPS WITH LIQUID CARBON DIOXIDE

The time course of the extraction of α-acids by liquid carbon dioxide was investigated and it has been established that there are two zones with greatly differing rates of extraction. The rate in the first zone is governed by ‘solubility’ effects, while in the second zone the rate is limited by ‘diffusional’ effects. Consequently the rate of extraction in the first zone depends upon the flow rate of liquid carbon dioxide while that in the second zone depends upon the time of extraction. The effects on extraction performance of the depth of the bed of hops and the extent of milling were also explored.     

THE DETERMINATION OF RESIDUES OF ETHYLENEBISDITHIOCARBAMATES AND THEIR HOMOLOGUES IN HOPS

Residues of ethylenebisdithiocarbamate and homologous fungicides are determined by hydrolysis with boiling sulphuric acid and colorimetric measurement of the liberated carbon disulphide. By its nature, the method is not specific for individual fungicides of this type but is simple and considered suitable for the screening of hop intake samples. Following the proposed introduction of a contractual residue limit of 60 mg/kg, this method was used by various laboratories to survey the 1980 and 1981 hop crops.     

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.     

ON THE QUANTITATIVE HIGH PRESSURE LIQUID CHROMATOGRAPHY ANALYSIS OF TRICYCLODEHYDRO-ISOHUMULONE IN HOPS AND BEER

HPLC analysis detected very small or even zero amounts of tricyclodehydro-isohumulone in hops or lagers.     

LIQUID CO2 AND ETHANOL EXTRACTION OF HOPS

The time-course of liquid carbon dioxide extraction of fresh and deteriorated hops was compared. The process of extraction becomes more difficult as hops deteriorate, which is reflected by the reduction in the LCV yield (g LCV/kg liquid carbon dioxide used). The extracts derived from deteriorated hops contain higher levels of uncharacterised soft resin. The pattern of elution of the latter does not allow the production of extracts low in uncharacterised soft resins and rich in alpha-acids.     

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.     

PROPOSALS FOR THE EFFICIENT AND ECONOMICAL USE OF HOPS IN BREWING

The hop lupulin glands, which contain the essential oils and resin acids, can be separated effectively from the bulky and worthless bracts and residues in a mechanical process which avoids solvent contamination. The separation is accomplished in an air stream through a centrifugal sifter after the lupulin has been rubbed off in a disc pin mill. The separated lupulin can be broken open by grinding in a colloid mill and used to obtain a dry hop aroma in beers by an ‘instant’ process. The lupulin can be used to bitter beers either directly in the copper or in a pre-boiling process. It can also be used in an aqueous extraction process to yield, nearly quantatively, pure and separate extracts of the α- and β-acids. The α-acids can then be isomerized almost quantitatively and the β-acids can be oxidized to give a 50% yield of hulupones. The hop residues, when boiled with wort, give an approximately 50% utilization of the remaining α-acids. These isohumulones can then be enhanced by those obtained from the extracted α-acids and the bitterness can be supplemented by the hulupones obtained from the β-acids. Overall, this process is calculated to give a bitterness utilization equivalent to 87% calculated on the original α-acids.     

VOLATILE ORGANOSULPHUR COMPOUNDS IN HOPS AND HOP OILS: A REVIEW

The nature of volatile organosulphur compounds occurring in hops and hop oils is reviewed. The effect of such compounds on beer flavour and their practical importance to the brewer are also discussed.     

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 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.     

VICINAL DIKETONES IN BEER. PART II: INFLUENCE OF SULPHUR DIOXIDE IN THE DETERMINATION OF DIACETYL IN BEER

The accuracy of the determination of diacetyl in beer using o-phenylenediamine is impaired by the presence of sulphur dioxide. This effect may be overcome when the distillate from the beer is collected in strongly acidic solution¹.     

HOP INDUSTRY COMMITTEE ANALYSIS OF HOPS OF THE 1983 CROP

Analytical values for α-acid content of thirteen varieties of hops from the 1983 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, in general, less than for previous years. As before, the results are acceptable for commercial purposes. The sampling rates have been considered and reductions in the rates for Bullion, Northern Brewer, Wye Northdown, Wye Target and Yeoman would be justified.     

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.     

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.     

LIQUID CO2 AND ETHANOL EXTRACTION OF HOPS PART III- EFFECT OF HOP DETERIORATION ON UTILISATION AND BEER QUALITY

The quality of beers bittered with liquid CO₂ and ethanol extracts derived from fresh and deteriorated hops and the percentage utilization of alpha-acids therefrom were comparable. The importance of using analytical methods which measure bitterness substances per se is emphasized.     

HOP INDUSTRY COMMITTEE: ANALYSIS OF HOPS OF THE 1979 CROP

Analytical values for α-acid content of thirteen varieties of hops from the 1979 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 six years. As before the results are acceptable for commercial purposes. The sampling rates have been considered and no changes can be justified.     

HOP INDUSTRY COMMITTEE: ANALYSIS OF HOPS OF THE 1980 CROP

Analytical values for α-acid content of thirteen varieties of hops from the 1980 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 a minor reduction in the rate for Wye Target is justified.     

HOP INDUSTRY COMMITTEE: ANALYSIS OF HOPS OF THE 1976 CROP

Analytical values for α-acid content of thirteen varieties of hops from the 1976 crop are presented in relation to the district of production. For eleven varieties the tolerance aim of ±0·5% was achieved; for two varieties there was a marginal excess in smaller growths. The results are considered acceptable for commercial purposes. α-Acid values for seedless hops from Hampshire and from the Seedless Hop Trials are included in the report and comparisons with seeded hops are shown over a three-year period.     

IMPROVEMENT OF THE BITTERNESS OF HOPS: PHOTOREACTIONS OF ALPHA ACIDS

The phototransformation of the α-acids (humulone) of hop resins has been studied in order to improve their bitter properties and to establish the optimal experimental conditions.