OXIDATIVE DEGRADATION OF ISOHUMULONES IN RELATION TO FLAVOUR STABILITY OF BEER

Isohumulones undergo oxidative degradation in bottled beer during shelf storage to give volatile compounds including 2-alkanones with chain lengths of C₃ to C₁₁, alkanals with chain lengths of C₂ to C₁₀ 2-alkenals of C₄ to C₇ or more and 2,4-alkadienals of C₆ to C₇. Since some resultant aldehydes are involved in the formation of stale aldehydes, very high levels of isohumulones in beer may cause considerable staling of beer flavour. Isohumulones were decomposed to these carbonyl compounds more easily than their derivatives, such as di- or tetrahydroisohumulones and humulinic acids, because the double bond or carbonyl group of the isohexenoyl side chain of the isohumulone molecule is involved in this degradation. This oxidation of isohumulones was greatly suppressed by addition of 300 ppm of sodium ascorbate or 40 ppm of ferrous ion.     

ALKALINE STEEPING AND THE STABILITY OF BEER

On the basis of the experimental evidence gathered in the course of this investigation, it is concluded that the alkaline steeping of barley leads to better colloidal (physical, non-biological) stability of the beer without significantly affecting its flavour or any of its standard characteristics. Since the alkaline steeping invariably lowers the tanninogen contents of malt (both anthocyanogens and catechins decrease), whereas its other principal analyses do not change in any predictable manner, it should follow that the tanninogen decrease is mainly responsible for better stability of the beer. It is also apparent that no malt characteristics, except tanninogen and protein contents, have a definite effect on the colloidal stability of the beer. A relationship between the tanninogen and protein contents of malt has also been established.     

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 LEAD IN BEER

Three procedures for the determination of low levels of lead in beer were evaluated and compared. The methods were (1) the existing IOB recommended procedure, (2) a dry ashing/AAS procedure and (3) a mixed solvent (xylene/2-heptanone) extraction of the DDDC complex. All three methods gave satisfactory results.     

A PACK STABILITY METHOD FOR MICROBIOLOGICAL TESTING OF LARGE CANS OF BEER

The microbiological stability of four-pint and seven-pint cans of beer can be determined by measuring the curvature of the ends after incubation at 28° C. A simple spherometer, a dial-gauge spherometer and a rig employing depth-transducers have been used in a simple, non-destructive method. This has revealed micro-biological defects more reliably than membrane filtration tests, and before “peaking” was visible to the eye. The method can also be adapted for sorting infected from non-infected cans in the warehouse.     

COLLABORATIVE DETERMINATION OF BEER FOAM STABILITY BY RUDIN AND NIBEM

Two methods, the “Rudin” method and the “Nibem” method have been tested for the determination of foam stability of beer by the Analysis Committee of the Institute of Brewing . For the Rudin method, over the range 90 to 102 seconds, it was judged that precision values were independent of the foam stability of the sample. Values for r₉₅ and R₉₅ were 6 and 22 seconds, respectively . For the Nibem method, precision was also independent of the foam stability of the sample over the range 213 to 246 seconds. Values for r₉₅ and R₉₅ were 22 and 70 seconds, respectively . The two methods ranked the foam stability of the three beers tested differently. This is to be expected, bearing in mind the different principles of the two procedures .     

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%.     

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 CARBON DIOXIDE IN BEER

A rapid, simple and inexpensive method is described for the determination of the carbon dioxide content of beers.     

THE ESTIMATION OF p-HYDROXYBENZYLAMINE IN BEER

A simple method has been developed to allow the estimation of p-hydroxy-benzylamine in beer in the presence of other amines including tyramine. Analysis of commercial beers has shown a low and variable content. At the levels found, p-hydroxybenzylamine seems unlikely to be of physiological significance even when monoamine oxidase inhibitor drugs are being taken. The biosynthetic route for p-hydroxybenzylamine has not been identified but synthesis of the compound appears to be associated with the barley husk.     

DETERMINATION OF SILICONE ANTIFOAM IN BEER

An atomic absorption method is described for the determination of polydimethylsiloxane residues in beer, in the concentration range 0.02–0.5 mg/litre. Actual levels found were 0.02–0.15 mg/litre from fermentations treated with 2–3 mg/litre silicones.     

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.     

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     

CHARACTERISATION OF BEER PARTICLE CHARGES AND THE ROLE OF PARTICLE CHARGE IN BEER PROCESSING

Streaming current measurement has been shown to be an effective tool in measuring the net charge of beer particles. Using this method, it was demonstrated that non-microbiological particles of a number of beers could be either positively or negatively charged. Copper fining has been shown to significantly affect the net charge of the NMP in the resultant beer. Increasing the copper fining rate enhances the negative net charge of the NMP to a limiting value at which the addition of further copper finings has no effect. This is believed to correspond to the complete removal of all of the positively charged NMP by copper fining. The reduction in pH during fermentation results in the production of further positively charged NMP. The presence of positively charged NMP has been shown to have an adverse effect on isinglass fining performance. These results suggest that choice of raw materials and process conditions play as much of a role in defining fining performance as does careful consideration of fining rates .     

硅胶、脯氨酰内肽酶处理对啤酒非生物稳定性的影响

采用SDS-PAGE电泳,对分别经硅胶吸附和脯氨酰内肽酶水解的啤酒后酵液进行蛋白分布研究;通过测定浊度和泡持性研究二者对啤酒非生物稳定性的影响.结果表明经硅胶吸附和脯氨酰内肽酶水解后的蛋白分子量均集中在8ku～14.4ku和35ku～45ku;经处理后的样品浊度明显下降,而泡持性没有显著变化.其中用脯氨酰内肽酶处理时浊度下降更明显.且对啤酒的泡持性影响更小.因此,在啤酒后酵液中添加脯氨酰内肽酶,能够有效的除去啤酒冷混浊蛋白.提高啤酒的非生物稳定性.     

甲醛替代产品DBP-1用于啤酒非生物稳定性的研究

在啤酒生产中使用甲醛替代产品DBP—1代替甲醛，研究其对啤酒的非生物稳定性的影响。试验过程中分别对最终麦汁、发酵情况、滤酒情况、成品感官和理化指标、保质期预到等方面进行了分析。试验结果表明在糖化过程中添加DBP—1，可生产出非生物稳定性和口感稳定性较好的啤酒。因此，在啤酒生产中可使用甲醛替代产品DBP--1。     

ANALYSIS OF LONG-CHAIN FATTY ACIDS IN BEER

A simple gas chromatographic method is presented for quantitative analysis of long-chain fatty acids in beer. Analytical results are quoted for ten different beers.     

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.     

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.     

DETERMINATION OF ALUMINIUM IN BEER BY GF-AAS

A method for the determination of aluminum in beer, has been collaboratively tested. The method tested relies on atomic absorption spectrometry with atomization in a graphite furnace. Five pairs of beers, with concentrations ranging from 96 to 1000 μg/litre, were analysed by eleven laboratories. The repeatability (r₉₅) values ranged from 10 to 69 μg/l, and the reproducibility (R₉₅) values ranged from 70 to 465 μg/l,. A second collaborative trial with a slightly different method protocol gave no improvement. Due to the high reproducibility values the method was not adopted for inclusion in Analytica-EBC.