COMPARISON OF TWO DISTILLATION—TITRIMETRIC PROCEDURES FOR THE ESTIMATION OF SULPHUR DIOXIDE IN BEER

The modified Monier Williams procedure as recommended by the Institute of Brewing (IoB) and the European Brewery Convention (EBC) for estimating sulphur dioxide in beer has been compared with the Tanner method. For both beer and aqueous solutions of sulphur dioxide the Tanner method, favoured by the E.E.C., gave significantly lower results than those obtained by the IoB/EBC procedure. It was established that the discrepancy between the results was due to the design and mode of use of the Tanner apparatus and not to differences in the reagents employed.     

THE DETERMINATION OF SULPHUR DIOXIDE IN BEER—COLLABORATIVE TRIAL OF FOUR METHODS

The Institute of Brewing Analysis Committee has collaboratively tested four methods for the determination of sulphur dioxide in beer over the range 1 to 40 mg/litre. The p-rosaniline method (r₉₅ = 0.51 + 0.10 m. R₉₅ = 0.63 + 0.26 m) was found to have the best precision and is recommended as an alternative to the Monier Williams method (r₉₅ = 0.43 + 0.15 m, R₉₅ = 1.86 + 0.27 m) where high precision at low sulphur dioxide levels is required. The dithiobisnitrobenzoic acid (DTNB) method and the IOB rapid distillation method showed considerably worse precisions.     

SPECTROPHOTOMETRIC DETERMINATION OF MALT COLOUR

The International Method for the determination of the colour of beer has been tested by members of the Analysis Committee of the European Brewery Convention on samples of wort produced from a laboratory extract of malt using methods EBC 4.4 and EBC 4.4.5. The method, which relies on the spectrophotometric determination of colour at 430 nm, on clarified worts, is recommended as the designated reference method in place of the current visual method using EBC colour discs. The change will take effect from 1st January 1996. It was judged that precision values were dependent on the intensity of the colour of the sample over the range 3.6 to 25.3 EBC units. Repeatability (r₉₈) and Reproducibility (R₉₈) values of r₉₈ 0.18Mean ? 0.28 and R₉₈ = 0.13Mean + 0.46 were obtained over this range.     

The degradation of folic acid in a model food system and in beer

The rate of degradation of folic acid in the light and in the dark is investigated in a model buffer solution and in beer, with and without the addition of sulphur dioxide.In the model solution, held in the light, sulphur dioxide markedly accelerates the rate of degradation of folic acid whereas, in the dark, it exhibits a protective effect. In beer, the presence of sulphur dioxide has no effect on the degradation of folic acid, whether in the light or the dark. In the model solution, in the presence of sulphur dioxide, only the degradation product p-aminobenzoyl glutamic acid was identified. In the absence of sulphur dioxide and in the beer samples, pterin-6-carboxylic acid was additionally identified as a degradation product.     

SO2与啤酒的风味稳定性

啤酒中含有一定量的SO2,SO2可由酵母产生,也可由外源添加的亚硫酸盐类物质产生。SO2对于保护啤酒的风味生物稳定性具有重要的作用,阐述了啤酒中SO2的来源、含量及在保护啤酒的风味生物稳定性等方面的作用。     

CO2 Correction Factor for the Net Contents of Containers

A new formula to replace the current EBC formula for the correction of net contents in beer containers for the presence of CO₂ has been derived from a bibliographic study that reviews the influence of carbonation on beer density determinations. The study reviews the relationship between beer density and CO₂ partial molal volume (PMV) as defined by the American Society of Brewing Chemists (ASBC) (ASBC Methods of Analysis Fills‐1 formula) and that given by the European Brewery Convention Analysis Committee (EBC) and shows that in the current EBC equation a CO₂ PMV of 0.65 mL/g and a residual CO₂ content after degassing of 0 v/v or % (m/m) is used. Experimental determination of CO₂ PMV gives values of 0.73 ± 0.01 mL/g for most of the standard European beers as Lager, Pilsener, Premium and Export styles. Residual CO₂ levels after decarbonation were quantified for a series of degassing methods and were found to be between 0.20 to 0.50 v/v average 0.40 v/v or 0.08% (m/m). A new equation for determining the CO₂ correction was then proposed assuming a PMV of 0.73 mL/g and a beer carbonation level of 0.40 v/v or 0.08% (m/m) after normal degassing. The new formula is recommended for inclusion in Analytica‐EBC replacing the current formula.     

二氧化硫对测定啤酒中双乙酰的影响

使用邻苯二胺(EBC法)测定啤酒中双乙酰含量时，啤酒中存在的亚硫酸氢盐会影响测定结果的准确性。而采用改进方法(CC法)可避免测定中的误差。通过对两种分析方法的对比实验，结果表明，使用EBC分析法测定时，二氧化硫会影响双乙酰的测定结果；而CC法具有高精确度和速度快的优点，该方法的主要不同之处是，蒸馏物是在强酸溶液中进行收集的。     

The impact of sulphur dioxide and oxygen on the behaviour of 2-furaldehyde in beer: an industrial approach

2‐Furaldehyde is often used as an analytical indicator of beer flavour deterioration. Although 2‐furaldehyde itself has a flavour threshold far above levels generally present in beer, it can be used as a good marker of heat damage of beer. A reversed‐phase liquid chromatographic assay, using ultraviolet‐visible detection, was applied to investigate the behaviour of 2‐furaldehyde throughout the brewing process and during extended storage of beer. The impact of storage temperature, sulphur dioxide and oxygen content on the level of 2‐furaldehyde was studied. It was found that the concentration of 2‐furaldehyde markedly increases during wort boiling and is rapidly reduced by yeast during the first hours of fermentation, emphasising the yeast reducing capacity as a determinant factor for the 2‐furaldehyde content found in the final beer. The results obtained suggest that sulphur dioxide and oxygen content play a key role on the 2‐furaldehyde content in packaged beer. 2‐Furaldehyde increase during ageing is oxygen dependent and sulphur dioxide retards its development by possibly protecting beer against the occurrence of oxidative reactions.     

Estimation of beer stability by sulphur dioxide and polyphenol determination. Evaluation of a Laccase-Sonogel-Carbon biosensor

The traditional methods used to evaluate parameters related to beer ageing have been tested, revised and criticised. With this aim, a sampling of lager beers has been carried out. Sulphur dioxide, polyphenols and antioxidant capacity have been determined in fresh and aged beer. Only sulphur dioxide concentration showed relevant differences after the ageing process. These results together with a correlation study provided information about the selectivity of the methodologies used and have made it clear that sulphur dioxide has an important role and polyphenols have an indirect role. Laccase-Sonogel-Carbon biosensor is proposed to determine polyphenols in beers instead of Folin–Ciocalteu assay due to its better selectivity, sensitivity and short assay times.     

Determination of the Total Soluble Nitrogen Content of Malt and Beer by the Dumas Combustion Method: Collaborative Trial

The determination of the total soluble nitrogen content of malt and beer, by the Dumas procedure, has jointly been collaboratively tested by the Analysis Committee of the Institute of Brewing (IOB) and the European Brewery Convention (EBC). Five samples of beer (range 362 to 1159 mg/l) and five samples of malt (range EBC 0.598 to 0.798 %m/m (dry basis) and IOB 0.534 to 0.706 %m/m (dry basis)) were distributed to eighteen participating laboratories for analysis. Precision values were judged to be independent of the mean soluble nitrogen content for malt by both IOB and EBC methodologies. Values for r₉₅ and R₉₅ were 0.047 and 0.136%m/m for EBC laboratory wort and 0.039 and 0.144 %m/m for IOB laboratory wort respectively. Precision values for beer were judged to be dependent upon the mean nitrogen content (m) in the case of r₉₅ and independent of the mean nitrogen content in the case of R₉₅. Values for r₉₅ and R₉₅ were 0.074m and 120 mg/l respectively.     

Determination of the N‐Nitrosodimethylamine Content of Beer and Malt — A Collaborative Trial

After about fifteen years a study was carried out to determine the variation in results of the N‐nitrosodimethylamine (NDMA) determination in beer and malt carried out in different laboratories, in order to obtain an overall view of the precision of the various methods used. Two collaborative trials were carried out by the EBC Analysis Committee during 1998. Repeatability values (r₉₅) for beer in the range of 0.09 ÷ 0.13 and for malt 0.33 ÷ 0.42 were found. Reproducibility values (R₉₅) for beer in the range of 0.45 ÷ 0.54 and for malt 0.65 ÷ 4.08 were obtained.     

DETERMINATION OF TOTAL VICINAL DIKETONES IN BEER BY HEADSPACE CAPILLARY GAS CHROMATOGRAPHY

The determination of total vicinal diketones in beer by the headspace capillary gas chromatography method of the Institute of Brewing Analysis Committee has been collaboratively tested by the members of the Analysis Committee of the European Brewery Convention. Two collaborative trials on three beer samples were performed in 14 laboratories. Repeatability (r₉₅) and reproducibility (Ras) values were obtained for 9 laboratories over the range of 20 to 90 μg. It was judged that reproducibility coefficients ranging after the second test from 32 to 94 were poor but it was decided that the method should nevertheless be included in the Analytica EBC as a guideline method with notice on its poor precision .     

DETECTION OF THE SULPHURING OF HOPS DURING KILNING AND CULTIVATION

Since brewing companies are now reluctant to accept hops treated with sulphur during kilning and cultivation, methods have been developed for detecting such contamination. In the procedure for estimating residual elemental sulphur, milled hops are continuously extracted with cyclohexane and dissolved sulphur is deposited on copper gauze as copper (I) sulphide. Hydrogen sulphide is then formed by the addition of hydrochloric acid and is absorbed in potassium hydroxide solution. The dissolved sulphide is finally estimated by titration using p-chloromercuribenzoic acid and diphenylthiocarbazone as indicator. The modified Monier Williams procedure, as recommended by the Institute of Brewing for estimating sulphur dioxide in beer, has been adapted for analysing hops. This provides a convenient technique for determining whether or not hops have been treated with sulphur or sulphur dioxide during kilning. The sulphur dioxide content of fresh hops treated at normal rates is of the order of 800 mg/kg. A number of samples of hops from the 1980 crop have been analysed and the levels of sulphur dioxide were found to be within the range 1 to 80 mg/kg. It is likely that these low levels are the result of using fuel oils, which contain variable amounts of sulphur, to dry the hops.     

二氧化硫与啤酒抗氧化性

论述了啤酒中二氧化硫的来源，酵母代谢形成二氧化硫的途径，发酵工艺条件对二氧化硫含量的影响，发酵过程产生的二氧化硫与人为添加的二氧化硫的差异性、二氧化硫与羰基化合物形成加成物的动力学模式、啤酒中二氧化硫含量变化以及影响因素。     

Determination of DMS and other Volatile Compounds in Beer by Headspace Capillary Gas Chromatography and Flame Ionisation Detection

The determination of beer volatiles by the headspace capillary gas chromatography with flame ionisation detection method of the Institute of Brewing Analysis Committee has been collaboratively tested by the members of the Analysis Committee of the European Brewery Convention and some members of the American Society of Brewing Chemists. Determined analytes were acetaldehyde, dimethylsulphide, ethylacetate, n-propanol, isobutanol, isoamylalcohols and isoamylacetates. The internal standards used were ethylmethyl sulphide and n-butanol. After three preliminary collaborative trials, a last fourth one was performed on three beer samples in 15 laboratories. Repeatability (r₉₅) and reproducibility (R₉₅) values were obtained for 12 laboratories. Assuming that too many members did not follow exactly the proposed method and judging that reproducitibility values were poor, it was decided to not include the method in the Analytica EBC as an official method, but to include it as a guideline method with the aforementioned notice.     

The Possibilities of Particle Analysis Demonstrated by the Measurement of the Colloidal Stability of Filtered Beer

Long‐term stability is one of the most important quality criteria of beer. Three groups of measuring methods are available for its determination: real time tests, predictive tests and indicative tests. One of the most common methods is the predictive forcing test, which is a time‐consuming method for accelerating beer ageing, e.g., at 0°C and 60°C. Two ways exist to perform this test: (1) follow‐up of haze development and determination of the lag phase or (2) the measurement of haze values after several days. The first option was evaluated by performing a long‐term Forcing test over a period of 4 months by analyzing a bottom‐fermented beer. It was shown that the haze curve followed a typical course with a lag phase, an increase phase and a stationary phase. Significant differences between the measurement after the cooling and the warm period were shown. In search of quicker methods and more accurate predictive indicators, the charge titration method was developed as an alternative to determine the particle charge of filtered beers, whereupon the relationship was elucidated between the increase in hazing and decrease of potential along with the advanced aging of beer. The results showed that with increased particle size due to agglomeration, the total charge decreased. In this array of trials, two differently stabilized beers were examined. Although both beers showed different haze values in the beginning (0.32 EBC and 1.30 EBC), the less stabilized beer had only 10 warm days and in contrast the beer with the good stabilization had over 20 warm days. With the help of the total charge, predictions were possible regarding the long‐term stability of the beer.     

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 .     

DISCRIMINATION BETWEEN BEERS WITH SMALL COLOUR DIFFERENCES USING THE CIELAB COLOUR SPACE

Commercial beers which recorded the same colours by either the European Brewery Convention (EBC) Recommended Method or by visual comparison against standard colour discs in a Lovibond Comparator, exhibited qualitative differences in their visible spectra. These differences, in turn, translated into measurable differences in colour, expressed as ΔE_a,b, when described by the CIELAB colour system. Visual difference tests revealed that, in some cases, beers with the same EBC colour could be discriminated by observers under ideal viewing conditions. A threshold value for ΔE_a,b, (which varied with EBC colour), below which no significant difference in beer colour could be detected by visual comparison, was determined by consideration of the corresponding ΔE_a,b, values for these beers. This threshold was used to assess the accuracy of a rapid method for colour analysis which uses transmittance values at five selected wavelengths. This new method was shown to give ΔE_a,b values, with respect to a reference method, which were within the limit of visually detectable colour differences. This, therefore, provides a valuable yardstick for assessing the worth of new tristimulus-based colour measurement techniques and instrumentation.     

啤酒中连二酮含量测定方法的比较与分析

对EBC法、气相色谱法和化学发光法测定啤酒中的双乙酰含量进行了优化和比较。结果表明，气相色谱法与其他两者相比，其能将戊二酮和双乙酰分离，能得到真正双乙酰的浓度，且重复性好，检测范围低，回收率高，可适合检测要求较高的场合。EBC法和化学发光法的重复性、回收率和检测限可达到常规分析的要求，但检测结果并不能反应双乙酰的真正浓度，可适合检测要求不高和常规分析。     

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.