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.     

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.     

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 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.     

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 MOISTURE CONTENT OF BARLEY

The method of the International Organization for Standardization, (ISO 712–1985) for the determination of moisture in cereals and cereal products, has been tested by members of the Analysis Committee of the European Brewery Convention on samples of barley. The method, which relies on loss in mass on drying at 130–133°C for 2 h, is recommended for use as a replacement for the current method, based on loss in mass on drying at 105–107°C for 3 h. It was judged that precision values were independent of concentration over the range 11 to 13% m/m. Repeatability (r₉₅) and Reproducibility R₉₅) values of 0.13 and 0.55 respectively were obtained over this range. At a mean level of 21.7% m/m, the r₉₅ and R₉₅ values were 0.27 and 2.6 respectively. This was probably due to errors associated with the double drying technique which is necessary for samples at this moisture content.     

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.     

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 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 DETERMINATION OF DIMETHYL SULPHIDE IN BEER BY HEADSPACE GAS CHROMATOGRAPHY — A COLLABORATIVE INVESTIGATION OF PRECISION

A method for the determination of dimethyl sulphide in beer by headspace gas chromatography has been collaboratively tested within ten laboratories of one brewing group at 3 levels from 19.8 to 52.4 μg/litre. The repeatability values (r₃₅ were found to be independent of concentration, but a strong linear relationship was found between the mean values (m) and the reproducibility value (R₃₅). The precision data can be summarised as r₃₅ = 3.3 μg/litre, R₃₅ = 3.66 + 0.168 μg/litre .     

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.     

DETERMINATION OF LOWER BOILING POINT VOLATILE COMPOUNDS IN BEER BY HEADSPACE GAS CHROMATOGRAPHY — COLLABORATIVE TRIAL

The Analysis Committee has collaboratively tested local routine headspace gas chromatographic methods for the determination of the lower boiling point volatile compounds in beer. The repeatability values (r₉₅) were dependent upon mean concentration (m) for acetaldehyde and alcohols but not for esters, whilst reproducibility values (R₉₅) were dependent upon concentration in all cases. The range of values of m and the estimates of r₉₅ and R₉₅ (mg/litre) for each compound were, respectively: acetaldehyde (5–8, 0.21m, 0.60m); propanol (9–23, 0.25m, 2.5+0.57m); isobutanol (5–22, 0.56+0.085m, 1.7+0.15m); methylbutanols (45–105, 0.14m, 0.22m); ethyl acetate (10–54, 3.1, 2.1+0.29m); isoamyl acetate (0.8–4.7, 0.36, 0.20+0.58m); and ethyl hexanoate (0.13–0.36, 0.073, 0.10+0.91m). No advantage was gained by diluting beer samples containing 9% V/V ethanol to 4% ethanol (used for the calibration mixtures) prior to analysis, but use of a standard method of sample preparation decreased most of the R₉₅ values. No recommendation is made in this interim report.     

DETERMINATION OF DIMETHYL SUPLHIDE IN BEER BY GAS CHROMATOGRAPHY — COLLABORATIVE TRIAL

The Analysis Committee has collaboratively tested both routine headspace gas chromatographic methods and a standardised method for the determination of dimethyl sulphide in beer using the flame photometric and flame ionisation detectors available in the participating laboratories. The mean repeatability value (r₉₅) was 7.8 μg/litre for the concentration range 12–65 μg/litre, and the reproducibility value (R₉₅) showed the relationship R₉₅ = 18.1 + 0.452m μg/litre to the concentration (m). No differences in precision were attributed either to the methods or the types of detectors used.     

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.     

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.     

DETERMINATION OF REPEATABILITY AND REPRODUCIBILITY OF EBC ACCEPTED METHODS IV—COLOURED MALTS

Methods for the determination of caramel and roasted malt moisture, extract and colour published in Analytica EBC have been collaboratively tested by the European Brewery Convention Analysis Committee, according to the ISO standard 5725. Repeatability (r₉₅) and reproducibility (R₉₅) values are presented.     

DETERMINATION OF REPEATABILITY AND REPRODUCIBILITY OF EBC ACCEPTED METHODS. III—BARLEY ANALYSIS

Methods for barley analysis published in Analytics EBC, 4th ed. have been collaboratively tested by the European Brewery Convention Analysis Committee and other European laboratories involved in Barley analysis. Repeatability (r₉₅) and reproducibility (R₉₆) values are presented. The answers to a questionnaire sent to all participating laboratories are discussed.     

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.     

ESTIMATION OF ISO-ALPHA-ACIDS IN BEER BY HPLC-COLLABORATIVE TRIAL

A procedure relying on high performance liquid chromatography for the estimation of iso-alpha-acids in beer has been collaboratively tested by the IOB Analysis Committee. In addition the trial samples were analysed by the IOB Recommended Method for the measurement of bitterness (BU). It was judged that the results obtained by the HPLC method were not sufficiently precise to permit adoption as a Recommended Method. However, since the method has the advantage of measuring bitterness in terms of iso-alpha-acids, it is suggested as an alternative to that of the Recommended Method. The iso-alpha-acids are absorbed from beer on to a C₁₈ Bond Elut column and then selectively desorbed prior to isocratic analysis by HPLC using an eluting solvent of methanol/water/phosphoric acid/tetrabutylammonium hydroxide and a C₁₈ radialpak cartridge. For both methods the repeatability values (r₉₅) were not dependent upon mean concentration (m) whereas the reproducibility values (R₉₅) were dependent upon concentration. The values of (r₅₃) and (R₉₅) obtained were 2.11 and (1.38 + 0.134 m) over the concentration range 13.8 to 34.0 mg/litre for the HPLC procedure and 1.20 and (0.76 + 0.122 m) over the concentration range 15.4 to 38.6 BU for the Recommended Method.     

EXTRACT AND COLOUR DETERMINATION OF TORREFIED PRODUCTS (WHEAT,BARLEY AND RYE)—COLLABORATIVE TRIAL

A procedure for preparing torrefied products for analysis has been examined and the effects of this procedure on the determination of laboratory extract and colour have been collaboratively tested by the Analysis Committee of the Institute of Brewing. White malts of DP levels 50° and 100° IOB were used as the sources of enzymes in the mixed mash procedure. With these malts r₉₅ and R₉₅ values for extract of the torrefied products ranged from 1.7 to 10.2 and 12.4 to 21.9 resp. on mean extracts ranging from 244 to 270 litre °/kg. The r₉₅ and R₉₅ values for colour ranged from 1.6 to 2.3 and 2.2 to 3.8 resp. on mean colours ranging from 2.7 to 3.5 EBC units.