USE OF EXTRACTS PREPARED WITH LIQUID CARBON DIOXIDE AS A SUBSTITUTE FOR DRY HOPS

Liquid carbon dioxide hop extracts were prepared for use as a substitute for dry hops. Many of these extracts were oil rich fractions containing up to 14% (w/w) hop oil. Extracts of Styrian Golding, Wye Target and Wye Northdown hops were used to treat ales prior to completion of beer processing and subsequent packaging. Emulsion/suspension systems were developed as carriers to facilitate addition of these extracts to beers before the chilling process. A loss of hop character from beer was found to occur during fining and filtration. Beers, treated with the extracts, exhibited natural though varietally distinct dry hop character. Production scale trials using these extracts have been successfully carried out to dry hop a brewery conditioned draught bitter and to match a traditionally dry hopped premium pale ale. The quantities of extract used indicated that economies in hop usage can be achieved when substituting liquid carbon dioxide hop extracts for dry hops.     

ORIGIN AND ESTIMATION OF THE GUSHING POTENTIAL OF ISOMERIZED HOP EXTRACTS

Two types of gushing promoter have been isolated from isomerized hop extracts. One type is a humulinicacid dehydration product which occurs rarely insuch extracts. The other type of gushing promoter consists of a mixture of oxidation products of hop resins, and is present in all the isomerized extracts examined. The higher the concentration of these oxidation products in a beer the greater is its tendency to gush. α-Acids and cohulupone have been shown to be effective gushing inhibitors. The gushing potential of an isomerized extract appears to be determined mainly by the relative proportions of oxidized materials and unchanged α-acid, present as contaminants. A method for determining the gushing susceptibility of a beer is described.     

EFFECTS OF PRODUCTS FROM SEEDLESS AND SEEDED HOPS ON BEER QUALITY

Comparative semi-industrial brewing trials with standard Continental lager beers have been carried out in Switzerland using hop pellets and hop extracts made from seeded and seedless hops. It has been demonstrated that the products from seeded hops containing 8% and 9% of seeds have no adverse effect on beer quality and that the flavour of all the beers was acceptable.     

SEPARATION AND QUANTIFICATION OF ALL MAIN HOP ACIDS IN DIFFERENT HOP CULTIVARS BY MICROEMULSION ELECTROKINETIC CHROMATOGRAPHY

Microemulsion electrokinetic chromatography has been applied to the analysis of hop acids in extracts of different hop cultivars. With this new analytical method, the 6 main hop bitter acids are completely separated within 10 minutes. Quantitative analyses of extracts from Saaz, Nugget and Wye Target cultivars have been compared to those obtained with reversed-phase high-performance liquid chromatography. The cohumulone and colupulone ratios are in good agreement. Microemulsion electrokinetic chromatography however is much faster and provides, in addition, data for the adhumulone and adlupulone ratios.     

PILOT SCALE BREWING TRIALS WITH SEEDLESS YEOMAN AND ZENITH HOPS

Beers of sound flavour and quality have been produced on the pilot-scale using the new hop cultivars, Yeoman and Zenith.     

QUANTITATIVE DETERMINATION OF HOP BITTER SUBSTANCES AND THEIR DERIVATIVES IN HOP EXTRACTS BY THIN LAYER CHROMATOGRAPHY

A method is described which allows the separation of hop bitter components and derivatives present in hop extracts by thin-layer chromatography on a mixture of silica gel and cellulose. This method can be used to evaluate the purity of hop extracts, isomerized hop extracts and complementary base extracts.     

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.     

INSTITUTE OF BREWING ANALYSIS COMMITTEE ANALYSIS OF HOP EXTRACTS AND ISOMERIZED HOP EXTRACTS

It is recommended that hop extracts should be examined qualitatively before the method of analysis is decided. Extracts would normally be analysed by the E.B.C. conductance method (and the results called “lead conductance values”) with a chromatostrip method as the alternative. Isomerized hop extracts should also be examined qualitatively, quantitative analysis being by the method of Wood, Lloyd & Whitear with countercurrent distribution as the recommended reference method.     

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.     

SIMULTANEOUS DETERMINATION OF α, β AND ISO-α ACIDS IN HOPS AND HOP PRODUCTS

A method for the simultaneous analysis of α, β and iso-α acid in hops, hop extracts and isomerised hop extracts is described. It is based on the use of reversed phase high performance liquid chromatography and quantitative evaluation of the hop compounds is carried out with a computing integrator. The isomerisation reaction can be examined in detail, particularly in connection with the production of hop derived haze forming compounds in isomerised hop extracts used for post fermentation bittering.     

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.     

FATTY ACIDS IN ISOMERIZED HOP EXTRACTS AND GUSHING

A procedure is described for the analysis of fatty acids (C₁₂-C₁₈ individually and C₁₈₊ as a group) in hops, hop extracts and isomerized hop extracts, and analytical results are quoted for twenty-one different samples of hops or hop products. Isomerized extracts varied widely in their content of fatty acids and isomerization and processing of hops appeared to eliminate some fatty acids selectively so that isomerized extracts were enriched in palmitic acid, linoleic acid and linolenic acid. Some hop extracts had a surprisingly high content of lauric acid. The analytical results are discussed in relation to gushing.     

LIQUID CO2 AND ETHANOL EXTRACTION OF HOPS PART I: EFFECT OF HOP DETERIORATION ON EXTRACTION EFFICIENCY AND EXTRACT QUALITY

Deteriorated hops were extracted with liquid carbon dioxide (LCO₂) and with ethanol. The degree of hop deterioration influences both the extraction efficiency and the composition of the resulting extracts.     

HOP RESINS AND BEER FLAVOUR V. THE SIGNIFICANCE OF OXIDIZED HOP RESINS IN BREWING

Oxidation products of α- and β-acids have been used to flavour beers. Ion-exchange chromatographic examinations of extracts of these beers are described. Examination of old hops has revealed the presence of certain oxidation products of hop resins.     

THE MANUFACTURE OF HOP CONCENTRATES AND EXTRACTS*

Manufacture of the traditional hop concentrate (i.e., a product containing the chemically unchanged natural hop constituents apart from useless inert material) is increasing both in Europe and in America; this traditional concentrate, which is added to the copper, retains the varietal characteristics of the parent hop. In determining replacement ratios it is important to assess bitterness by tasting trials, as analytical assessments of bitterness may give misleadingly low results when concentrates are used. Although chemically pre-isomerized extracts can be prepared for addition to sweet beer, it is improbable that this type of extract will be used extensively until a great deal more is known about transformations which take place during hop boiling; such an extract, however, does allow maximum utilization of hop bittering principles. The selection of hops for high α acid content and the separate addition of the flavour components such as hop oil appears to be a desirable development for the near future.     

AUTOMATED REPORTING ON THE QUALITY OF HOPS AND HOP PRODUCTS

The quality of a hop variety or a hop product can readily be assessed by a fully automated sequence of selective extraction, fractionation and quantitative analysis. To illustrate the elegance of the method, nine hop varieties and three hop extracts were compared with respect to the content of important marker compounds in the hop oils and of the hop acids. Supercritical fluid extraction at different densities of carbon dioxide was applied to extract selectively, the hop oils and the hop acids, respectively. The hop oils were further fractionated into an apolar and a polar fraction by solid phase extraction and consecutive elution with n-hexane and ethyl acetate. Separation and identification were achieved by capillary gas chromatography coupled to mass spectrometry. Myrcene, β;-caryophyllene, α;-humulene and β;-farnesene in the apolar fraction, linalool, undecan-2-one, tridecan-2-one and humuladienone in the polar fraction were selected for quantitative evaluation of the respective hop oils. Sulphur-containing compounds were revealed by capillary gas chromatography using sulphur-selective atomic emission detection. Complete separation and quantification of all hop α;-acids and β;-acids was effected by microemulsion electrokinetic chromatography coupled to diode array detection .     

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.     

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.     

QUANTITATIVE ANALYSIS OF HOPS AND HOP EXTRACTS BY HIGH PRESSURE ION EXCHANGE CHROMATOGRAPHY

A new analysis for hop acids in hops and hop extracts is described. It is based on recent developments in high pressure liquid chromatography using pellicular anion exchange column filling material. Quantitative evaluation of α-acids, β-acids and oxidation products in hops and hop extracts is carried out by standard addition of pure humulone. The α-acids are completely separated from other hop substances before quantitation. The results of α-acids determinations must therefore be more accurate than was formerly possible and they are compared with conductometric titration results which are systematically higher. This is to be expected as it becomes more and more obvious that paper strip and conductometric analysis are not selective enough and determine fractions as “α-acids” which are in fact oxidation products of the hop acids.     

THE HIGH PERFORMANCE LIQUID CHROMATOGRAPHY OF HOP RESINS

Hop resins are eluted from a specially developed weak anion exchange bonded phase silica using citric acid, methanol, water, mixtures as eluent. Fresh and deteriorated hops and isomerized extracts have been examined. The ratio of the humulone congeners in different hop varieties and the conversion of α-acid to iso-α-acid during the hop boil have been measured.