THE INSTITUTE OF BREWING ANALYSIS COMMITTEE THE DETERMINATION OF VICINAL DIKETONES IN BEER

A survey of a number of methods for the determination of the diacetyl content of beer resulted in the recommendation for routine use of a colorimetric technique based on the method of Owades, Jakovac & Vigilante. The method is both simple and rapid in operation but is not specific for diacetyl, estimating also other related diketones. It was felt, however, that the estimation of vicinal diketones was advantageous since the results were more in line with aroma assessment. The Analysis Committee appointed the following Sub-Committee to recommend a method for the determination of diacetyl in beer:– R. G. Ault (Chairman), M. O. Jones, J. R. Hudson, G. A. Howard, P. A. Martin P. F. Bayles, L. R. Bishop, R. N. Greenshields, L. Taylor, A. Sinclair (co-opted). The findings of the Sub-Committee are given in this paper.     

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 .     

THE INFLUENCE OF 2-ACETOHYDROXY ACIDS ON THE DETERMINATION OF VICINAL DIKETONES IN BEER AND DURING FERMENTATION

During sampling and determination of diacetyl, 2-acetohydroxy acids are easily converted to vicinal diketones. A simple procedure for gas chromatographic determination of diacetyl, 2-acetolactate, acetoin and the homologous compounds is given. By careful sampling, less than 0·01 ppm of diacetyl was detected during the main fermentation in one brewery, whereas another strain of brewer's yeast yielded a maximum of 1·7 ppm of diacetyl. When samples of fermenting liquids are exposed to air at 60°C, complete conversion of 2-acetohydroxy acids takes place in less than one hour. The possibility that part of 2-acetolactate may be converted to acetoin, however, cannot be excluded. In finished beer 2-acetolactate levels of 0·2–0·5 ppm were observed. During the main fermentation the values ranged from 0·5–2·5 ppm.     

A COMPARISON OF COLORIMETRIC METHODS AND A GAS CHROMATOGRAPHIC METHOD FOR THE DETERMINATION OF VICINAL DIKETONES IN BEER

Colorimetric methods recommended by the American Society of Brewing Chemists (Reference method A and Micro method C), the European Brewery Convention and the Institute of Brewing and a new gas chromatographic method have been compared using three beer types (lager, ale and barley wine). Reference method A of the American Society of Brewing Chemists gave the best reproducibility and recovery of added diacetyl for the colorimetric methods but the gas chromatographic method was the best of all the methods and is recommended for quality control use.     

DETERMINATION OF DIACETYL IN BEER USING DIFFERENTIAL-PULSE POLAROGRAPHY

A Polarographie method is proposed for the determination of diacetyl and other vicinal diketones in beer. Similar to the EBC official spectrophotometric method, diacetyl is derivatised with o-phenylene-diamine, producing 2,3-dlmethylquinoxaline, a polarographically active compound . The Polarographic method allows discrimination between diacetyl and methylglyoxal and a detection limit ten times lower than the EBC method is obtained. In addition, problems of erratic results for diacetyl may be avoided and data are in good agreement with those obtained by gas chromatography with electron capture detection and headspace sampling . It is suggested that high results obtained with the spectrophotometric method may be attributed to an erroneous procedure used in the spectrophotometric calculations. An alternative procedure is proposed, with which lower values for diacetyl in beer are obtained, similar to those found with other methods. These low diacetyl values are near the detection limit of the spectrophotometric method .     

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.     

A SEMI-AUTOMATIC METHOD FOR THE GAS CHROMATOGRAPHIC DETERMINATION OF VICINAL DIKETONES IN ALCOHOLIC BEVERAGES

A method has been developed for the routine determination of diacetyl and pentanedione in alcoholic beverages. After the addition of internal standard and any necessary dilution, a stream of nitrogen swept the components of the sample at a fixed temperature to a 2 ml injection loop of a gas chromatograph fitted with an electron capture detector. The data from the chromatograph were collected on cassette and processed by computer. The time between starting temperature equilibration of the sample and obtaining the diketone content as μg/litre beverage was about 17 min. The coefficient of variation for diacetyl was 1·8% (5·1%, with manual injections) and for 2,3 pentanedione 1·6% (9·1%) for replicated analyses of the same sample.     

DETERMINATION OF VICINAL DIKETONES IN BEER BY GAS CHROMATOGRAPHY (HEADSPACE TECHNIQUE)—COLLABORATIVE TRIAL

Two methods for the determination of vicinal diketones in beer have been collaboratively tested by the Analysis Committee of the Institute of Brewing and are recommended for use. Both methods employ gas chromatography and are essentially the same, except that one relies on the use of a packed column and the other on a capillary column. For diacetyl it was judged that repeatability (r₉₅) values were independent of concentration over the range 0.04 to 0.19 mg/litre. Over this range, r₉₅ values for diacetyl of 0.028, 0.020 and 0.026 mg/litre were obtained for capillary, packed columns and combined results respectively. Values for reproducibility (R₉₅) were judged to be dependent on the mean level (m). R₉₅ values were 0.032 + 0.68 m, 0.01 + 0.47 m and 0.005 + 0.67 m were obtained for capillary, packed columns and combined results respectively. For both methods the r₉₅ and R₉₅ values for 2,3-pentanedione were judged to be independent of concentration over the range 0.02 to 0.07 mg/litre. For capillary columns, packed columns and combined results respectively, r₉₅ values were 0.009, 0.009, 0.010 mg/litre and R₉₅ values were 0.037, 0.042 and 0.038 mg/litre.     

测定啤酒中双乙酰含量的改进EBC法

该文介绍了一种快捷、可靠的测定啤酒中双乙酰含量的分析法。与EBC分析法一样,这种新的测定法也是以光谱估计测定法为基础,通过对这2种方法的比较得出。在改进方法中得到的数据证明其速度和精确度比EBC分析法有了较大的改进。     

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。     

THE DETERMINATION OF CARBON DIOXIDE IN BEER

The Analysis Committee of the EBC has collaboratively tested a manometric and a titrimetric method for carbon dioxide determination. The relative merits and errors associated with each method are assessed.     

SOME FACTORS AFFECTING THE CONCENTRATION OF DIACETYL IN BEER

Investigations of factors affecting the production of diacetyl during fermentation have shown large differences in the abilities of different strains of brewer's yeast to produce diacetyl. Studies on pilot scale and on small laboratory fermentations have established a connection between the concentration of amino acids in the wort and that of diacetyl in the fully fermented beer. Control of the ratio of amino acids to sugars in wort is thus an important factor in maintaining concentrations of diacetyl in beer at an acceptable level. The effects of increased pitching rate and of high-temperature fermentation in enhancing the production of diacetyl are demonstrated.     

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。     

COLOUR DETERMINATION OF BEER USING TRISTIMULUS VALUES

The derivation off tristimulus and chromaticity values for beers, using transmission measurements, is discussed. Chromaticity values indicate that the majority of beers have colours which resemble those represented by the EBC colour scale. However, the dilution of dark beers for colour analysis, according to Recommended Methods, leads to non-standard colours. The colour adjustment of beers, using colouring agents, can also produce colours which deviate markedly from the standard EBC colour range. On this basis, the adoption of tristimulus measurement for quantification of beer colour is proposed. A method for obtaining tristimulus values of beers, based on transmission measurements at 5, 6 or 7 wavelengths, gives results comparing favourably with those from standard procedure, which requires transmission measurements at 5 nm, 10 nm or 20 nm intervals across the entire visible spectrum.     

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.     

操作条件对双乙酰测定的影响

研究各种操作条件对ＥＢＣ分析法测定啤酒中双乙酰的影响,得到了较有价值的结果。     

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.     

成品啤酒中双乙酰含量的控制

本文讨论成品啤酒中双乙酰含量回升原因及保证双乙酰含量在啤酒保质期内符合要求的工艺控制措施；通过双乙酰测定采用不同方法所得结果的比较。     

CURRENT LAGER BEER TECHNOLOGY IN CONTINENTAL EUROPEAN BREWERIES AND ESPECIALLY IN GERMAN BREWERIES*

Following a comparison of beer production and consumption in different EBC countries, a survey is made of technological developments in German breweries. This survey covers raw materials, wort production, fermentation and maturation, and changing procedures are discussed in terms of production economics and product quality.     

THE IDENTIFICATION OF CARBONYL COMPOUNDS IN BEER

Carbonyl compounds were separated from bottom-fermented lager beer by extraction with a diethylether-pentane mixture and precipitation from the extract with 2,4-dinitrophenylhydrazine. The diketones, diacetyl and 2,3-pentanedione, were identified as bishydrazones by thin-layer chromatography with benzene-petroleum ether-ethyl acetate (34:5:1) as solvent and Silica Gel HF₂₅₄ as adsorbent. For the identification of the aldehydes, the hydrazone precipitate was treated with ozone in formic acid solution and the aldehydes were determined as their corresponding carboxylic acids by iso-thermal gas chromatography on a NEGS column. Aldehydes were found in the following order of magnitude: acetaldehyde, isobutyraldehyde, isovaler- and/or opt.act.valeraldehyde (2-methylbutyraldehyde), valeraldehyde and butyraldehyde.