DETERMINATION OF MOISTURE,TOTAL AVAILABLE EXTRACT AND SOLUBLE EXTRACT IN SPENT GRAINS

The methods for the determination of moisture⁴, total available^3,4 and soluble extracts⁴ in spent grains have been collaboratively tested by members of the Analysis Committee of the European Brewery Convention to obtain repeatability (r₉₅) and reproducibility (R₉₅) values . Repeatability and reproducibility values of 0.1 and 0.67 respectively were obtained for spent grain moisture's ranging between 4 and 8% m/m in pre-dried and pro-milled samples. In a pro-dried and unmilled sample containing 3.4% m/m moisture the values obtained were 0.3 and 1.5 respectively . For total available extract (MEBAK) these values were 0.5 and (2.2+0.045 m) respectively, with total available extract ranging from 9 to 42% m/m dry matter, where m refers to the actual value. The values for the pre-dried and unmilled sample containing an extract of 41.2% m/m were 0.5 and 4.6 respectively . The precision values for soluble extract were dependent on the extract level of the sample over the range 6 to 40% m/m dry matter. A repeatability value of 0.13+0.007 m and a reproducibility value of 0.2+0.06 m were obtained over this range. Values for the same pre-dried and unmilled sample with a soluble extract of 38.7% m/m were 1.3 and 3.8% m/m respectively .     

DETERMINATION OF ANIONS IN BEER BY ION CHROMATOGRAPHY

A method relying on ion chromatography, with suppressed ion detection, for the determination of anions in beer, has been collaboratively tested by members of the American Society of Brewing Chemists, the European Brewery Convention and the Brewery Convention of Japan. Precision values obtained for the determination of chloride, sulphate and phosphate in beer were judged to be acceptable. Repeatability (r₉₈) and reproducibility (R₉₈) values for chloride were 5.7, 12.6, 12.5 and 15.0, 38.4, 36.8 respectively at corresponding mean levels of 68.7, 218.6 and 322.5 mg/litre. r₉₈ and R₉₈ values for sulphate were 7.5, 6.2, 7.6 and 44.8, 54.0, 46.5 respectively at corresponding mean levels of 101.4, 205.1 and 122.6 mg/litre. r₉₈ and R₉₉ values for phosphate were 14.1, 11.9, 24.9 and 78.7, 53.8, 84.0 at corresponding mean levels of 411.5, 224.1 and 397.5 mg/litre. Whilst the r₉₈ value for nitrate was acceptable, the value for R₉₈ was unsatisfactory. The ion chromatographic method for determining chloride, sulphate and phosphate in beer is recommended for use and inclusion in Analytica -EBC as an International Method.     

DETERMINATION OF ETHANOL IN BEER BY DIRECT INJECTION GAS CHROMATOGRAPHY: A COMPARISON OF SIX IDENTICAL SYSTEMS

Six identical gas chromatographic (GC) systems from the same manufacturer were evaluated for the determination of ethanol in beers. Each system was assessed for detector linearity and drift using standard ethanol solutions. Repeatability (r₉₅) of each machine, repeatability (r₉₅) of the GC method and reproducibility (R₉₅) of the method over a range of ethanol concentrations (1–11% V/V) was determined using commercial beers. All six instruments were linear over the ethanol range 0–12% V/V and were in good agreement. Drift of the machines was negligible over the period of the analysis. Over the ethanol range 0.95 to 6.32% V/V the repeatability (r₉₅) and reproducibility (R95) values were 0.050 and 0.083 respectively. Over the ethanol range 9.48 to 11.15% V/V the repeatability (r₉₅) and reproducibility (R₉₅) values were 0.153 and 0.227 respectively. Comparison of the precision values and those obtained in a recent IOB Analysis Committee Collaborative¹ for the determination of ethanol by gas chromatography showed no significant differences between the two methods. The reported method is suitable for determination of ethanol in beers.     

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.     

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 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 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 THE MOISTURE AND NITROGEN CONTENTS OF BARLEY AND MALT BY NEAR INFRARED SPECTROSCOPY (NIRS)

The determination of the moisture and nitrogen contents of barley and malt by near infrared spectroscopy (NIRS) has been tested by the Analysis Committee of the European Brewery Convention. In the collaborative trial four samples of barley and malt were analysed by 17 laboratories. Repeatability (r₉₅) and reproducibility (R₉₅) values of 0.3 and 1.5% m/m respectively were obtained for barley moisture over the range 12.7 to 15.8% m/m. For malt moisture these values were 0.2 and 1.3% m/m over the range 4.0 to 4.3% m/m, for barley nitrogen 0.1 and 0.3% m/m on dry matter over the range 1.57 to 2.14% m/m, and for malt nitrogen 0.1 and 0.2% m/m on dry matter over the range 1.58 to 1.82% m/m, respectively.     

COLLABORATIVE DETERMINATION OF SPECIFIC GRAVITY BY DENSITY METER

A method employing a density meter for the determination of specific gravity (SG) has been tested for the determination of the gravity (G) of beer, aqueous sugar solutions and aqueous ethanol solutions by the Analysis Committee of the Institute of Brewing. The term “gravity”, used throughout this report is defined by the equation G = SG × 1000. Repeatability (r₉₅) and reproducibility (R₉₅) values were calculated over the range 994.6 to 1124.2 gravity. For beer, it was judged that precision values were independent of the gravity of the sample. Values for r₉₅ and R₉₅ were 0.1 and 0.9, respectively, for instruments with a 5 figure display and 0.08 and 0.32, respectively, for instruments with a 6 figure display, over the range 999.1 to 1017.0 gravity. For solutions of ethanol in water, precision was also independent of the gravity of the sample. Values for r₉₅ and R₉₅ were 0.1 and 0.3, respectively, for instruments with a 5 figure display and 0.05 and 0.19, respectively, for instruments with a 6 figure display, over the range 994.6 to 999.1 gravity. For aqueous sugar solutions the values of r₉₅ and R₉₅ increased with increasing gravity. At 1049.3 gravity, values for r₉₅ and R₉₅ were 0.1 and 0.8, respectively, for instruments with a 5 figure display and 0.07 and 0.35, respectively, for instruments with a 6 figure display. At 1124.2 gravity values for r₉₅ and R₉₅ were 0.2 and 1.4, respectively, for instruments with a 5 figure display and 0.16 and 1.35, respectively, for instruments with a 6 figure display.     

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.     

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 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.     

ESTIMATION OF α- AND β-ACIDS IN HOP EXTRACTS BY HPLC

A procedure relying on high performance liquid chromatography for the estimation of α-acids and β-acids in hop extracts has been collaboratively tested by members of a Sub-Committee of the Institute of Brewing Analysis Committee and is recommended for use. No significant differences were found between precision values obtained using peak height and peak area measurements. For α-acids, the mean repeatability (r₉₅) and reproducibility (R₉₅) values were 1-3 and 2-4% m/m respectively over the range 41–62% m/m. For β-acids they were 0-9 and 2-0% m/m respectively over the range 11 to 35% m/m. The precision values were judged to be independent of concentration.     

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 REPEATABILITY AND REPRODUCIBILITY OF THE REVISED METHOD FOR GERMINATIVE CAPACITY

The method for the determination of germinative capacity of barley using hydrogen peroxide and peeling technique (EBC 3.5.2) was revised in 1995. The revised procedure has been collaboratively tested by the EBC Analysis Committee. The repeatability (r₉₅) and reproducibility (Rob) values were dependent upon mean values, r₉₅ = (64.23-0.64m) % and R₉₅ = (51.74-0.50 m) % .     

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.     

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.     

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.     

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.     

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.