ESTIMATION OF VOLATILE SULPHUR COMPOUNDS IN BEER

A method has been developed for the quantitative estimation of volatile sulphur compounds in beer at levels below 0.1 μg litre^?1. The method relies on the concentration of beer headspace volatiles onto a porous polymer followed by injection into a capillary gas chromatographic column using a thermal desorption cold trap injector. The volatile components are separated using temperature programming and detected by a flame photometric detector specific for sulphur compounds. The mean concentrations and the estimates of r₉₅ (μg litre^?1) for volatile sulphur compounds measured in a commercial lager were respectively: methanethiol (0.33, 0.30); dimethyl sulphide (19.3, 5.3); carbon disulphide (0.42, 0.32); ethylene sulphide (0.37, 0.05); 1-propanethiol (0.11, 0.02); methyl thioacetate (11.7; 2.7); methyl disulphide (0.34, 0.42). The method is a significant improvement over previous techniques for the quantification of sulphur-containing volatiles in beer .     

BICYCLIC ISOMERISATION PRODUCTS OF HUMULONE AND COHUMULONE IN BEER

Separation of five- and six-membered ring hop acids can be obtained selectively by High Performance Liquid Chromatography (HPLC) on anthracene-bonded silica gel. Photo-diode array detection combined with high resolution HPLC of the six-membered compounds of beer reveals the presence of I and II in Fig. 1. These compounds are formed by reaction of the respective α-acids, humulone (III) and cohumulone (IV), in brewing conditions.^1,2 Their concentration in beer is a few μgl^?1.     

THE USE OF 14C-LABELLED POLYPHENOLS TO STUDY HAZE FORMATION IN BEER

Haze formation in beer is claimed to involve the gradual polymerization of polyphenols and their subsequent reaction with proteins to form insoluble complexes. The mechanism of haze formation has now been studied using ¹⁴C-labelled epicatechin and dimeric catechin. Epicatechin does not polymerize to form dimeric or trimeric polyphenols when beer is stored and is only incorporated into beer haze to a small extent. Some of the epicatechin combines with nitrogen-containing compounds during storage to form soluble complexes. However, dimeric catechin does not form soluble complexes with nitrogen-containing compounds and instead there is a substantial incorporation of this dimer into beer haze. Dimeric polyphenols are important haze precursors which form insoluble complexes with one or more of the polypeptides of beer, probably by an oxidative coupling mechanism.     

MEASUREMENT OF RESIDUAL CARBOHYDRATE IN BEER

No standardized method exists for the determination of total or individual carbohydrates in beer and this could cause difficulties in view of regulatory requirements for labelling. A comparative study of known methods likely to be most suitable for the measurement of total carbohydrate in beer was therefore undertaken. Methods were also examined for estimating other important residual carbohydrates in beer, such as residual fermentable carbohydrates, β-glucan, total fructose and fructosans, and total pentose and pentosans. The beers analysed covered a wide range of carbohydrate levels and, as expected, the different methods gave different values for the carbohydrate content of the same beer. We consider that the colorimetric anthrone-sulphuric acid procedure (Yadav's version) is to be preferred for estimating the total residual carbohydrate content of beer. It is less prone to interference, relatively simple, rapid and gives more accurate results than acid or enzymic hydrolysis in combination with reductometric procedures. The within-laboratory coefficient of variation is 1.68%.     

THE DETECTION OF ISINGLASS FININGS IN BEER

A method for the detection of isinglass finings in beer is described. Protein is precipitated from the beer with a large excess of sodium alginate and hydrolysed; the hydrolysate is examined colorimetrically for the presence of hydroxyproline. The presence of this imino acid, which is found in substantial proportions only in collagen and gelatin, indicates that the beer has been fined.     

酶制剂在啤酒品质改良中的应用

啤酒的澄清度、色度、风味、稳定性、持泡性是衡量其品质的重要因素，介绍了几种改良啤酒品质的酶制剂。     

CONTROL OF SULPHURY IMPURITIES IN BEER AROMA

Volatile sulphur compounds, particularly hydrogen sulphide and mercaptans, are normal products of yeast metabolism. Although they tend to be purged out of beer during fermentation and maturation, it is not uncommon for finished beer to retain enough of them—up wards of 0·02 ppm as sulphur—to impair its aroma. The addition of a small amount of copper sulphate to sulphury beer cleanses its aroma by transforming volatile sulphur into non-volatile copper sulphide and mercaptides, but since a considerable proportion of this added copper is liable to be inactivated by complexing with nitrogenous constituents of the beer, the removal of sulphur may necessitate the addition of so much copper as to threaten the shelf life of the beer. It has been found that not only may traces of copper be dosed electrolytically into beer with great precision but that the copper so dosed reacts nearly quantitatively with the volatile sulphur present, thus abolishing the latter with no appreciable increase in the net copper content of the beer. The process has given satisfactory results on an industrial scale, improving the flavour of beers without prejudice to their other characteristics.     

METHODS FOR THE DETERMINATION OF VOLATILE NITROSAMINES IN MALT,WORT AND BEER

Methods for the analysis of beer, wort and malt for NDMA at the one in 10⁹ level using the thermal energy analyzer have been evaluated. The beer and wort procedure using Preptube extraction has been shown to give excellent results. For malt, the preparation of an aqueous extract, followed by analysis by the beer procedure, also gives excellent results. Vacuum distillation from mineral oil has also been examined for the analysis of malt. Providing sufficient aqueous phase is initially present, this procedure yields results similar to those from aqueous extraction. The methods will also detect NDEA, although no NDEA has been observed in any of the beer, wort or malt samples examined. NDMA has been observed to be present in bound forms in malt and Preptubes and is released by the addition of water     

GAS CHROMATOGRAPHIC DETERMINATION OF TRIHYDROXYOCTADECENOIC ACIDS IN BEER

A rapid and quantitative method for measuring the content of trihydroxyoctadecenoic acids in beer is described. The acids are extracted from degassed beer with ethyl acetate and methylated with diazomethane. After washing, the methylated compounds are silylated and analysed by gas chromatography. The coefficient of variation of the method is 3·2%. The amounts of total trihydroxyoctadecenoic acids in commercial beer samples varied from 4 to 12 mg/litre. The effects of these acids on beer flavour and head retention are discussed.     

THE BITTERNESS OF HOP-DERIVED MATERIALS IN BEER

The bitterness of trans- and cis-isohumulones obtained both from beer and by alkaline isomerization of α-acids has been compared with the bitterness of hop resins and other materials extractable from beer. Trans-isohumulones and cis-isohumulones, obtained either from beer or by alkaline isomerization of α-acids, and hulupones have been shown to be the most bitter materials. Hulupones were only slightly less bitter than trans-and cis-isohumulones, which showed little difference in bitterness value when prepared directly, although the collective tasting results show a bias for a greater bittering associated with the cis-component. The hulupones, like the parent β-acid, possessed a distinctive aromatic flavour. α-Acids and other unidentified materials obtained from beer brewed with hops of a normal age have been found to possess a much lower level of bitterness. The observation that aged hops impart normal levels of tastable bitterness to beer has been confirmed at significant brewery level (60 brl.) using grists consisting solely of six year old hops. Approximately 35% of this bitterness is provided by isohumulones and the greater part of the remainder arises from materials soluble in low-boiling paraffinic hydrocarbon solvents. A known β-acid oxidation material has been isolated from fresh and old hops and from beers brewed with either fresh or old hops.     

PECTINATUS,A NEW GENUS OF BACTERIA CAPABLE OF GROWTH IN HOPPED BEER

The properties of a new bacterial genus that is capable of growth in hopped beer are described. The organism is an anaerobic gram-negative, non-spore forming mesophilic rod with flagella emanating from one side of the cell body. It produces a considerable amount of H₂S and high turbidity when grown in packaged beer. No alcohol was produced from glucose unlike the genus Zymomonas. The guanine-plus-cytosine content of the deoxyribonucleic acid is 39.8 mol %. The physical and biochemical characteristics of this organism indicate that it is not related to any of the brewing bacteria so far reported in the literature including the genus Zymomonas. We have proposed the new genus and species Pectinatus cerevisiiphilus in the family Bacteroidaceae⁶. The type strain has been deposited in the American Type Culture Collection (ATCC) under the number 29359.     

THE DETERMINATION OF PAPAIN IN BEER

The quantitative determination of papain in beer has been achieved by means of turbidity measurements on a casein substrate. The method, which is quick and simple, will measure activities of the order of 1–20 p.p.m. of crude papain. This will cover any amount likely to be found in beer     

THE CONCENTRATION AND SIGNIFICANCE OF PYRUVATE IN BEER

Excretion of pyruvate takes place during the yeast-growth phase of fermentation, and, in batch fermentation, the extent of its accumulation varies directly with the extent of growth. Pyruvate excretion is not related to the content of pyruvate decarboxylase in the cells and is not influenced by the addition of thiamine or alanine to the wort; the pH of the wort exerts a slight influence on pyruvate excretion. Pyruvate may be metabolized by yeast towards the end of fermentation and during conditioning, so that the quantity present in beer is influenced by the extent and timing of yeast separation. The addition of sodium pyruvate to beer alters beer flavour by affecting the ‘mouth feel’ aspect of flavour; the minimum quantity required to do this varies in different beers over a range of 50–400 mg/litre.     

铁离子对啤酒质量影响的研究

就铁离子对啤酒质量的影响进行了研究，结果表明铁离子能够促进啤酒沉淀物的形成，加速啤酒老化现象的产生，铁离子与自由基的产生有直接的关系。因此，在啤酒中应降低铁离子的含量，以降低其对啤酒质量造成的影响。     

RADIOIMMUNOASSAY OF PAPAIN IN BEER

A radioimmunoassay (RIA) of papain is described which is capable of detecting 0·2 μg of papain/ml in beer, a level approximately 1% of that normally used for chillproofing. Changes in incubation conditions significantly accelerates the papain determination with only slight loss of accuracy. Apart from the high sensitivity it has been shown that the method is highly specific and distinguishes papain from the other chillproofing enzymes used.     

DETERMINATION OF TOTAL CARBOHYDRATE IN BEER

A colorimetric procedure for the determination of total carbohydrate in beer has been evaluated in a collaborative trial. The method is recommended by the Analysis Committee.     

DETERMINATION OF NITRATE IN BEER BY ION CHROMATOGRAPHY

¹A method, relying on ion chromatography, for the determination of nitrate in beer, has been collaboratively tested by members of the European Brewery Convention (EBC) and the Brewery Convention of Japan (BCOJ). Precision values were judged to be acceptable. Repeatability (r₉₅) and reproducibility (R₉₅) values were 1.5, 0.96, 5.1, and 9.3, 10.4, 13.5 respectively for corresponding mean levels of 6.5, 26.2 and 52.8 mg/litre. However, r₉₅ and R₉₅ values of 1.5 and 2.3 respectively were obtained for an aqueous solution of nitrate ions at a mean level of 20.7 mg/litre. The determination of nitrate is recommended for use and inclusion in Analytica-EBC, as an additional analyte in the International Method which relies on ion chromatography for estimating chloride, sulphate and phosphate.     

A VERY SENSITIVE METHOD FOR ASSAYING PROTEOLYTIC ACTIVITIES IN BEER

A very sensitive method for assaying chillproofing enzymes in beer is described using denatured ¹²⁵I-labelled human serum albumin as a substrate (40°C, pH 6.0 and 30 min reaction time). Less than 0.1 ug of papain in 1 ml of beer has been determined by this method. The results achieved by the proposed method were in good correlation with immunochemical and ‘hide power azure’ (HPA) methods.     

NUCLEOTIDES IN BEER

Nucleotidic material was isolated by anion exchange chromatography of beer on a Dowex 1 × 8 (formate) column. Ultraviolet spectroscopy and retention volume data suggested the presence of cytidine monophosphate (CMP) [max. 5 mg/litre], in one of the fractions. No other mononucleotides were detected. Chromatography of charcoal extracts of beer on DEAE Sephadex A25 failed to yield a fraction containing mononucleotides. Triangular taste tests indicated that addition of adenosine-5′-monophosphate (AMP) and guanosine-5′-monophosphate (GMP) to beer (30 mg/litre and 25 mg/litre respectively) did not cause significant flavour changes.     

THE ISOELECTRIC FOCUSING OF BEER PROTEINS IN POLYACRYLAMIDE GEL

A technique has been developed for fractionating beer proteins by isoelectric focusing in polyacrylamide gel which enables protein species with isoelectric points differing by as little as 0·1 pH unit to be separated as clearly defined bands. The isoelectric profile of an all-malt beer was found to be similar to that of the parent wort but significant changes occurred when a beer was stabilized in the laboratory by three different treatments.