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 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.     

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 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 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 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.     

THE DETERMINATION OF ALCOHOL IN BEER USING THE SCABA AUTOMATED METHOD (COLLABORATIVE TRIAL)

The Institute of Brewing Analysis Committee has organised two collaborative trials for the analysis of alcohol using the ServoChem Automatic Beer Analyser (SCABA). The mean repeatability (r₉₅) values for the two trials were 0.051% and 0.034% V/V respectively. The value for the second trial could however be judged to be dependent on concentration (m) at 0.008m% V/V. The Reproducibility (R₉₅) values of both trials were judged to be dependent on concentration at 0.027m% V/V and 0.025m% V/V respectively. The combined data for the two trials gave r₉₅ = 0.044% V/V and R₉₅ = 0.026m% V/V.     

ESTIMATION OF FERMENTABLE CARBOHYDRATES — COLLABORATIVE TRIAL

A procedure relying on high performance liquid chromatography, for the estimation of fermentable carbohydrates in wort, has been tested collaboratively and adopted by the Institute of Brewing Analysis Committee as a Recommended Method. A radially compressed cartridge containing silica modified with tetraethylenepentamine is used with an eluting solvent of acetonitrile/water. The results of a preliminary trial indicated that better precision is achieved using manual measurements of peak height and omitting an internal standard. In the main trial where 5 laboratories analysed 5 sample pairs the repeatability (r₉₅) and reproducibility (R₉₅) values found with their mean concentration levels (m) to which they are applicable were: fructose (0.0256 + 0.0660m) and (0.0711 + 0.0691m) for 0.17–1.01 g/100 ml; glucose 0.090m and 0.139m for 0.80–2.07 g/100 ml; sucrose 0.095 and (0.0746 + 0.1663m) for 0.12–3.88 g/100 ml; maltose 0.219 and 0.917 for 4.17–6.09 g/100 ml; maltotriose 0.122 and 0.236 for 0.97–1.19 g/100 ml. The precision values for the sums of the total fermentable sugars were 0.578 and 1.040 for 6.71–14.24 g/100 ml.     

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 S-METHYLMETHIONINE IN MALT BY ALKALINE HYDROLYSIS AND HEADSPACE GAS CHROMATOGRAPHY - A COLLABORATIVE TRIAL

The Institute of Brewing Analysis Committee has collaboratively tested routine methods for the determination of S-methylmethionine in malt. Eleven participating laboratories each used their own method of alkaline hydrolysis followed by headspace gas chromatographic determination of the resultant dimethyl sulphide. Mean repeatability values r(95) were 1.21 and 2.47mg/kg, and mean reproducibility values R(95) were 4.30 and 5.60 mg/kg for mean concentrations of 5.00 and 7.27 mg/kg respectively.     

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 .     

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.     

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 .     

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.     

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 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 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.     

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 GERMINATION PERCENTAGE AND GERMINATION INDEX—COLLABORATIVE TRIAL AND RUGGEDNESS TESTING

A method for the determination of Germination Percentage and Germination Index in malting barley has been tested by the EBC Analysis Committee and approved for inclusion in Analytica-EBC. In the collaborative trial three pairs of barley samples with high, medium and low vigour were analysed by 16 laboratories. The r₉₅ values for the Germination Percentage ranged from 0.5% to 6.3% and the R95 values ranged from 0.5% to 8.7% increasing with lower level of mean germination percentage. The r₉₅ values for the Germination Index ranged from 0.29 to 0.74 and the R95 values ranged from 0.97 to 1.20. The ruggedness testing of the Germination Index shows that the factor temperature has a minor, but significant effect on the result, the factors time for the first count together with the volume of water, have major significant effects. The tested factors have no significant effect on Germination Percentage.     

NEW MASHING SYSTEM FOR DETERMINATION OF LABORATORY EXTRACT

The method of preparation of laboratory wort by the Tepral mashing system provides a clear improvement in the evaluation of industrial malts and in the optimization of malting procedures. The equipment required is simple and easy to operate. The use of the method has shown significant differences in terms of both wort viscosity and extract yield between malt from 2-row spring barley (variety Carina) and malt from 2-row winter barley (variety Sonja), produced under identical industrial conditions: the Sonja malt gave fewer good results for finely ground malt than did the Carina malt.