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 .     

DETERMINATION OF THE VOLATILE COMPONENTS OF BEER

A method relying on headspace sampling and gas chromatography for the determination of the lower boiling point volatile compounds (fusel oils) in beer, has been approved by the Analysis Committee of the Institute of Brewing (IOB), for inclusion in Recommended Methods of Analysis. In view of the large values obtained for precision in terms of repeatability (r₉₅) and reproducibility (R₉₅) and the differences in gas chromatographic equipment used by individual brewing laboratories, the method is considered not to be ideal, but is given as a guideline only. The IOB Analysis Committee has recommended a method relying on gas chromatography and flame photometric detection for the determination of dimethyl sulphide in beer. Repeatability (r₉₅) and reproducibility (R₉₅) values of 3.3 μg/litre and 3.66+0.168 m μg/litre (where m is concentration), respectively, were obtained over the range 20–50 μg/litre. Methods currently used in brewing laboratories, for the measurement of vicinal diketones, are being surveyed with a view to obtaining a suitable method for collaborative testing by the Analysis Committee.     

DETERMINATION OF SOLUBLE NITROGEN BY SPECTROPHOTOMETRY

A simple spectrophotometric method for the determination of nitrogen in unhopped wort has been tested by the EBC Analysis Committee and accepted for inclusion in Analytica-EBC. The spectrophotometric method is intended as a quick method for routine quality control. It is emphasized that the procedure has to be followed in detail and that the precautions stated under Notes on Procedure are most important. The average precision values obtained for the range 600 to 850 mg/litre were r₉₅=30 and R₉₅ = 104.     

COLLABORATIVE DETERMINATION OF THE PH OF BEER AND WORT

A method for the determination of pH in wort and beer has been tested for precision by the Analysis Committee of the Institute of Brewing . Over the pH range 3.94 to 5.04 it was judged that precision values were independent of the pH value of the sample. Values for r₉₅ and R₉₅ were 0.025 and 0.129 respectively .     

DETERMINATION OF HOT WATER EXTRACT

The Analysis Committee of the European Brewery Convention has recommended that the Hot Water Extract procedure for malt, which relies on a coarse grind and single temperature mash (65°C), is included in Analytica-EBC, as an additional method to that of the EBC Extract procedure. The Committee accepted the precision values obtained by the Institute of Brewing on the 1984 Check Malt. Repeatability (r₉₅) and reproducibility (R₉₅) values in litre degrees/kg were 2.14 and 3.48 respectively, for mean value of 295.3 at a Miag 0.7 mm setting, and 1.93 and 2.90 respectively, for a mean value of 298.2 at a Miag 0.2 mm setting.     

THE DETERMINATION OF BEER COLOUR—COLLABORATIVE TRIAL

The data and analyses on which the Institute of Brewing based its decision to modify its method for the determination of beer colour are presented. Spectrophotometric measurements at 430 nm are shown to be more precise than measurements made at 530 nm or by using comparators. The Institute of Brewing Analysis Committee recommends that measurement at 430 nm is adopted. Equations relating precision to beer colour determinations at 430 nm are advanced.     

ESTIMATION OF ENDO BETA-GLUCANASE ACTIVITY IN MALT USING A VISCOMETRIC METHOD

A viscometric method for estimation of endo beta-glucanase activity in malt has been collaboratively tested by the Institute of Brewing Analysis Committee. Ten participating laboratories analysed five pairs of malt samples in the range 176 to 1238 IRV units. The repeatability (r₉₅) values ranged from 22 to 122 IRV units and the reproducibility (R₉₅) values from 93 to 650 IRV units. The results indicated that R₉₅, but not r₉₅, was dependent on endo beta-glucanase activity. Overall precision values were 76.8 for r₉₅ and 0.506Mean + 4.786 for R₉₅. It was decided that the method would be included in IOB Methods of Analysis but that attention would be drawn to the poor precision values obtained in this and previous collaborative trials.     

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.     

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 .     

INSTITUTE OF BREWING ANALYSIS COMMITTEE: Interpretation and Meaning of Analytical Results

The meanings of the terms “precision” and “accuracy” are discussed in relation to analyses carried out in brewery laboratories and to specifications which may be drawn up for different analytical attributes of brewing materials. The rôle of the Analysis Committee of the Institute of Brewing is outlined.     

DETERMINATION OF ETHANOL IN BEER BY GAS CHROMATOGRAPHY (DIRECT INJECTION)—COLLABORATIVE TRIAL

A method employing gas chromatography for the determination of ethanol in beer has been collaboratively tested by the Analysis Committee of the Institute of Brewing. It was judged that precision values were independent of concentration over the range 0.93 to 6.05% V/V ethanol. Repeatability (r₉₅) and reproducibility (R₉₅) values of 0.061 and 0.136 respectively, were obtained over this range. At a mean level of 9.17% V/V, the r₉₅ and R₉₅ values were 0.154 and 0.284 respectively. This was probably due to dilution errors as the sample had to be diluted to bring it within the linear range of the method. A comparison of the precision values given by the gas chromatographic method, with those obtained in 1991/1992 by 8 laboratories in a major brewing company using 12 sample pairs, for the IOB Recommended Distillation Method, revealed that there is no significant difference between the precision data for the two methods.     

Analytica‐EBC — Precision Values of Wort Analyses

In Analytica‐EBC (1) method 8.3: Specific Gravity of Wort by Density Meter, method 8.4: Viscosity of Wort: Glass Capillary Viscometer (IM), method 8.5: Colour of Wort: Spectrophotometric Method (IM), method 8.7: Fermentable Carbohydrates in Wort by HPLC (IM), method 8.8: Bitterness of Wort (IM), method 8.9.1: Total Nitrogen in Wort: Kjeldahl Method and method 8.11: Zinc in Wort by Atomic Absorption Spectrophotometry (IM) are described, but repeatability (r₉₅) and reproducibility (R₉₅) values are missing. These methods have been collaboratively tested by members of the Analysis Committee of the European Brewery Convention in 1999 to obtain the corresponding precision data. In method 8.12: Total Polyphenols in Wort by Spectrophotometry the precision values are missing as well, but because of testing a new ammonium ferric citrate reagent the data have been postponed. The worts analyzed had extract contents of ca 18°P (% m/m), 14°P, 12°P, 10°P and 8°P respectively. The precision values are listed below (n = number of participating laboratories, m = mean value).     

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.     

COLLABORATIVE TRIAL ON THE DETERMINATION OF BETA-GLUCANASE IN MALT BY VISCOMETRIC AND DYE-LABELLED METHODS

The results of a collaborative trial to compare a dye-labelled beta-glucan method with that of a viscometric procedure, for estimating the beta-glucanase content of malt, have demonstrated that overall the precisions of both methods are similar. There has been an improvement in the precision of the viscometric method (which is not a Recommended Method) compared with values obtained in previous trials. The Institute of Brewing Analysis Committee judged that the results obtained by the dye-labelled beta-glucan method were not sufficiently precise to permit adoption as a Recommended Method. However, since this procedure has advantages of speed and ease of operation, it is suggested as an alternative method to that relying on viscometry. It is envisaged that a further collaborative trial will be carried out when sufficient experience of the new method has been obtained. The repeatability (r₉₅) and reproducibility (R₉₅) values found were 0.190 m and 0.327 m over the concentration (m,U/kg) range 92–266 U/kg for the dye-labelled method, and 0.173 m and (91.4 + 0.0717 m) over the concentration (m,IRV) range 233–701 IRV units for the viscometric method.     

DETERMINATION OF TOTAL NITROGEN IN BARLEY AND MALT BY COMBUSTION METHOD—COLLABORATIVE TRIAL

A combustion method, relying on the Dumas principle, for the determination of total nitrogen in barley and malt, has been collaboratively tested by the Analysis Committee of the European Brewery Convention. Repeatability, r₉₅, and reproducibility, R₉₅, values were 0.063 and 0.116% of dry matter, respectively, for samples with nitrogen contents in the range 1.23 to 1.86% N of dry matter. There was no significant difference between these values for barley and malt. The Analysis Committee approved the adoption of the combustion method for inclusion in Analytica EBC as an alternative method.     

DETERMINATION OF THE SOLUBLE IRON CONTENT OF FILTER AIDS: A COLLABORATIVE TRIAL

The international method for the determination of the soluble iron content of filter aids has been collaboratively tested by members of the Analysis Committee of the European Brewery Convention to obtain repeatability (r₉₈) and reproducibility (R₉₈) values. It was Judged that precision values were dependent on the quantity of the soluble iron content of the filter aids over the range 32 to 220 mg/kg. Repeatability (r₉₈) value of 0.050 m and reproducibility value (R₉₈) of 0.255 m were obtained over this range.     

新型捻线机匀捻器的研发及应用

深入剖析了先进直捻机的关键部件———匀捻器 ,并对其动平衡精度进行了推算 ,提出了应用过程中故障修复的解决办法     

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.     

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.     

REFRACTOMETRIC MEASUREMENT OF ORIGINAL GRAVITY

A refractometric procedure for the measurement of Original Gravity has been evaluated and compared with the Official distillation procedure in a collaborative trial. The refractometric method is recommended by the Analysis Committee as an alternative to the official distillation procedure for control purposes within brewing companies.