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.     

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.     

ANALYSIS OF ISOMERIZED HOP EXTRACTS PART I. ESTIMATION OF ISOHUMULONES

A rapid spectrophotometric method for the estimation of the isohumulone content of isomerized hop extracts is described. This method has given acceptable reproducibility even in the hands of inexperienced personnel; it also gives results in close agreement with those obtained by counter-current distribution techniques, which are also 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.     

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.     

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.     

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.     

THE SUPPRESSION OF GUSHING BY THE USE OF HOP OIL

The addition to beer of small amounts of hop oil provides a means of suppressing gushing, without adversely affecting foam stability. The hydrocarbon fraction of hop oil is a more effective gushing suppressor than the oxygenated fraction.     

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.     

RELATIONSHIP BETWEEN FUSARIUM INFESTATION OF BARLEY AND THE GUSHING POTENTIAL OF MALT

Fifty barley samples, displaying a range of 0 to 100% kernels infested with Fusarium, were collected in North Dakota, South Dakota, and Minnesota during the harvest of 1994. Samples were micromalted, and the levels of the fungal metabolites, deoxynivalenol and ergosterol, were determined. Fusarium infestation and the levels of fungal metabolites were evaluated as predictors of gushing in laboratory trials. Malt samples which were infested with Fusarium or contaminated with the fungal metabolites exhibited a propensity to gush. However, only the levels of deoxynivalenol and ergosterol were found to be strongly correlated with the actual amount of gushing observed. This suggests that their production may parallel that of the component which actual causes gushing, and that screening barley and malt for these metabolites, may offer a means of reducing gushing problems in the brewery. Determination of deoxynivalenol is rapid, when it is present, and necessary because of food safety and malt quality concerns.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.