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.     

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 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 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 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 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.     

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.     

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.     

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.     

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 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 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.     

Partition coefficient of migrants in food simulants/polymers systems

Partition coefficients of six migrants (ethyl acetate, acetaldehyde, acetonitrile, methyl ethyl ketone, isopropyl acetate and butyraldehyde) were determined between four food simulants (water, 10% ethanol, 3% acetic acid and 95% ethanol) and two polymers (polyamide and polyethylene terephthalate). The results showed that partition coefficient is highly dependent on the nature of the migrant, polymer and food simulant. Of the six migrants, acetonitrile and ethyl acetate had the highest affinity for polar food simulants such as water, 10% ethanol and 3% acetic acid. Partition values for systems containing 95% ethanol as a food simulant were higher for non-polar migrants and lower for polar migrants.     

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.     

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 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 .     

Optimization of extraction parameters for quantification of fermentation volatile by‐products in industrial ethanol with solid‐phase microextraction and gas chromatography

The rapid growth of the biofuels industry resulted in new research needs in chemical analysis. Methods for screening and quantification of impurities resulting from changes in feedstock, process and purification are needed. Direct sample injection methods are often not sensitive for lower concentrations. This research, developed an analytical method to simultaneously quantify fermentation volatile by‐products in industrial corn‐based ethanol. These include acetaldehyde, ethyl vinyl ether, 1,1‐diethoxyethane, isoamyl alcohol, isoamyl acetate, styrene, 2‐pentylfuran, ethyl hexanoate, ethyl octanoate, and ethyl decanoate. Headspace solid‐phase microextraction (SPME) coupled with gas chromatography–mass spectrometry (GC–MS) and GC‐FID were used. The effects of SPME coating, concentration, time, and salting out were tested. The optimized method used Carboxen/PDMS 85 µm coating with 10% (v/v) ethanol, 20 s headspace extraction, and no salt addition. The method had values of R² between 0.93 and >0.99 and relative standard deviations between 0.10 and 11.96%. The method detection limits were between 9.5 × 10^?4 to 9.7 × 10^?8 mol/L.This is one of the most comprehensive quantification methods for volatile impurities in raw ethanol to date. This new method was used to quantify 10 prevalent impurities in corn‐based industrial ethanol. Copyright © 2015 The Institute of Brewing & Distilling