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 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 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 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.     

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 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 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.     

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 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.     

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.     

Cold dryer as novel process for producing a minimally processed and dried meat

In this study, it was aimed to design a novel dryer that operates at low temperature (≤20 °C) for the production of a minimally processed and dried meat, and to determine the drying characteristics of this product. Beef slices loaded into this dryer were dried at different low temperatures (10, 15 and 20 °C) and air flow rates (1, 2, 3 and 4 m/s) after pasteurization. The drying time of slices was significantly influenced by the temperatures and air flow rates. The shortest drying time that pass until reaching the final water content (40%) was found in the slices subjected to a temperature of 10 °C and an air flow rate of 4 m/s. Nine kinetic models were selected to evaluate the moisture ratio data, with regard to adjusted regression coefficient (R²), the reduced chi-square (χ²) and root mean square error (RMSE). Page model exhibited the best fit (R² ≥ 0.9961; χ² ≤ 0.0002 and RMSE ≤ 0.0125). In addition, the effective moisture diffusivity (D_eff) and activation energy (E_a) values of slices were 7.13 × 10⁻¹⁰ m²/s and 44.96 kJ/mol, respectively. Consequently, the low drying temperature could shorten the drying time of beef because the driving force for mass transfer is supplied by the moisture difference between food and the air in the dryer.Industrial relevanceThe novel dryer could carry out minimal processing to the meat, provide food safety and perform drying in cold conditions (≤20 °C). Beef slices dried faster with a drying temperature of 10 °C and an air flow rate of 4 m/s in this dryer. Various dried products also could be obtained by cold drying method without the loss of their quality properties.     

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 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.     

INFLUENCE OF SAMPLE SIZE AND SHAPE ON TRANSPORT PARAMETERS DURING DRYING OF SHRINKING BODIES

An experimental investigation on the influence of sample size and shape on heat and mass transport parameters under natural convection air‐drying is presented. Potato cylinders with length of 0.05 m and thicknesses of 0.005, 0.008, 0.010 and 0.016 m, and circular slices with diameter of 0.05 m and thickness of 0.01 m were dried in a laboratory scale hot‐air cabinet dryer. Results indicate that each transport parameter exhibits a linear relationship with sample thickness. Convective heat and mass transfer coefficients (h_cand h_m) decreased whereas moisture diffusion coefficient (D_eff) increased with increasing thickness. Considering no sample shrinkage effect in the parameter analysis, for the thickness range considered, the values of h_care found to be underestimated in the range of 29.0–30.6%, whereas those of h_mand D_eff are overestimated in the range of 33.7–38.0% and 75.9–128.1%, respectively. Using Levenberg–Marquardt algorithm for optimization, a correlation for Biot number for mass transfer (Bi_m) as a function of drying time and sample thickness is proposed. A close agreement was observed between dimensionless moisture contents predicted by this relation and those obtained from experiments for different sample thicknesses at drying air temperature of 60C. For the same thickness and drying conditions, circular slices caused an increase in each transport parameter significantly.     

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.     

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.     

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.     

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.     

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 .