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.     

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.     

HUMULINIC ACID IN ISOMERIZED HOP EXTRACTS

Humulinic acid, which is not bitter, behaves similarly to iso-α-acids in some analytical estimations of beer bitterness. The humulinic acid content of a number of isomerized hop extracts was estimated using thin layer chromatography.     

ISOMERIZED HOP EXTRACTS IN EXPERIMENTAL BREWING

The later that isomerized hop extracts were added during the brewing process the better was the utilization. Thin layer chromatography of the beers produced from a range of experimental brews using isomerized hop extracts showed that the ratios of the various bitter substances derived from hops differed only slightly. The utilization of isomerized extract is enhanced if residues normally discarded during the manufacture of extracts are added to wort.     

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.     

ISO-α-ACIDS CONTENT OF ISOMERIZED HOP EXTRACTS

Two chromatographic procedures for the analysis of iso-α-acids in isomerized extracts have been tested. Although one of the methods—a variant of the Hansen, Hetzel & Miller procedure—performed better than the other, it still falls short of the demands of commercial transactions. The methods available for the assay of iso-α-acids are reviewed.     

RAPID SPECTROPHOTOMETRIC METHOD FOR DETERMINATION OF THE BITTERING VALUE OF ISOMERIZED HOP EXTRACTS

A method is described which allows the rapid determination of the bittering value of isomerized hop extracts. The method is also applicable in the case of isomerized hop extracts containing impurities such as α-acids and β-acids.     

ESTIMATION OF ISOHUMULONES

Analytical results obtained by six methods of estimating isohumulones in worts and beers are examined. It is shown that, by use of appropriate factors, data obtained from alkaline methanol solutions containing isohumulones and humulones can be converted to give quantities of isohumulones equivalent to those as measured in iso-octane, so overcoming the apparent discrepancies in the results obtainable from the several methods. It is suggested, on the basis of many analyses, that with iso-octane washed with acid methanol the factor 34·8 instead of 28·6 be used to convert absorption at 275 mμ. to p.p.m. of isohumulones in the solutions as read.     

ESTIMATION OF LEAD CONDUCTANCE VALUES FOR HOP EXTRACTS CONTAINING WATER-SOLUBLE FRACTIONS

A rapid method is described for estimating the lead conductance values of hop extracts containing water soluble fractions.     

EUROPEAN BREWERY CONVENTION: ANALYSIS COMMITTEE SUB-COMMITTEE ON ANALYSIS OF HOPS AND EXTRACTS METHODS OF ANALYSIS OF HOP EXTRACTS

For the conductometric analysis of hop extracts the method described by Bishop,⁶ is satisfactory provided the extract is composed entirely of resins; extracts which contain additional water-soluble material should be analysed by an abbreviated Wöllmer technique. For isomerized extracts a qualitative examination should first be made, either by paper-strip chromatography or by thin-layer chromatography. A rapid counter-current distribution procedure is suitable for the analysis of isomerized extracts: the modified Rigby & Bethune method²² is appropriate only with extracts which are known to be free from α and β acids.     

ANALYSIS OF HOP EXTRACTS BY SIMPLIFIED COUNTER-CURRENT DISTRIBUTION METHODS

Simplified counter-current distribution procedures are described which allow correct analysis of the α acids and iso α acids content of hop extracts.     

EUROPEAN BREWERY CONVENTION: ANALYSIS COMMITTEE SUB-COMMITTEE ON ANALYSIS OF HOPS AND EXTRACTS METHODS OF ANALYSIS OF HOP EXTRACTS

The EBC has adopted the method put forward by the German Commission for Brewing Analysis for the conductometric evaluation of hop-extracts which contain water-soluble material.     

EFFECT OF STORAGE ON HOP EXTRACTS

Representative commercial hop extracts suffered no appreciable loss either of α- or β-acids or of bittering value when kept for 2 to 21 months in closed containers. Though there was loss of α- and β-acids on prolonged exposure of the extracts to air, it did not lead to a corresponding loss of bittering value. Of a range of commercial isomerized extracts, most proved satsifactorily stable on storage. However, when large losses of iso-α-acids did occur they were accompanied by corresponding reductions in bittering value. With reference to bittering compounds, there appeared to be no significant differences in the storage stability of beers bittered using hops or extracts of various types.     

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 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.     

PREPARATION OF HOP EXTRACTS WITHOUT USING ORGANIC SOLVENTS

Extraction of hops with liquid carbon dioxide at ambient temperature provides an attractive means of producing hop extracts which are rich in α-acids and free from hard resins, polyphenols, pigments and residual organic solvents. The resulting yellow extracts give beer with a clean bitter flavour when they are added during wort boiling. Manufacturing costs using the process are likely to be substantially less than in a conventional hop extraction plant.     

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.     

THE CHEMISTRY OF HOP CONSTITUENTS. PART XXXV. INTERCONVERSION OF HUMULONE AND ISOHUMULONE

Isohumulone reverts partially to humulone in solution or in sealed tubes under the influence of heat.     

ESTIMATION OF α- AND β-ACIDS IN HOP EXTRACTS BY HPLC

A procedure relying on high performance liquid chromatography for the estimation of α-acids and β-acids in hop extracts has been collaboratively tested by members of a Sub-Committee of the Institute of Brewing Analysis Committee and is recommended for use. No significant differences were found between precision values obtained using peak height and peak area measurements. For α-acids, the mean repeatability (r₉₅) and reproducibility (R₉₅) values were 1-3 and 2-4% m/m respectively over the range 41–62% m/m. For β-acids they were 0-9 and 2-0% m/m respectively over the range 11 to 35% m/m. The precision values were judged to be independent of concentration.     

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.