Determination of Boiled Wort Colour

A method for the determination of boiled wort colour has been collaboratively tested by the Analysis Committee of the European Brewery Convention. In this trial the 14th EBC Standard Malt and two commercial malts were tested by 21 laboratories. Repeatability (r₉₅) and reproducibility (R₉₅) values of 0.33 ? 0.42 and 1.12 ? 1.44 EBC units were obtained respectively at a mean level of 4.7 ? 5.2 EBC units. At a mean level of 8.9 EBC units these respective values were 0.44 and 2.25 EBC units. The data sets could be split into two sub?sets for laboratories using either the included heating plate boiling procedure or the glycerol/oil bath boiling procedure. Statistical analysis of both sub?sets revealed that reproducibility is unambiguously better for the glycerol/oil bath procedure at all levels. For repeatability the situation is less clear. The evaluated method is recommended for inclusion in Analytical?EBC.     

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.     

MALT DIASTATIC ACTIVITY. PART II. A MODIFIED EBC DIASTATIC POWER ASSAY FOR THE SELECTIVE ESTIMATION OF BET A-AMYLASE ACTIVITY,TIME AND TEMPERATURE DEPENDENCE OF THE RELEASE OF REDUCING SUGARS

Ammoniumcitrate, sodium EDTA and ammonium oxalate were tested as possible inhibitors of α-amylase in the EBC diastatic power assay. A contact time of 90 min at a concentration of 0·1 M ammonium oxalate was shown to inactivate α-amylase completely in the enzymic malt extract while only very slightly enhancing β-amylase activity. The selective release of reducing sugars by β-amylase in the diastatic power assay was evaluated as a function of time using a p-hydroxybenzoic acid hydrazide assay and compared with that of the diastatic power procedure with the same colourimetric technique. The diastatic power results of eight different malts are well correlated with those of the β-amylase activity (r² = 0·98). In a linear regression model the diastatic power results at 20°C of the same malts correlated better with results obtained at 55°C (r² = 0·77) than with those obtained at 60°C (r² = 0·63). For the results of β-amylase activities we found r² = 0·86 for the relation between the activities at 20°C and at 55°C and r² = 0·92 for the relation between the activities at 20°C and 60°C. Since the temperature conditions (20°C) of the EBC-diastatic power assay do not correspond to those of brewing practice it is suggested that the activity of β-amylase as well as the malt diastatic power be evaluated at 55°C.     

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.     

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 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 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) % .     

Effect of High Temperature‐High Humidity Treatment of Germinated Unkilned Barley on Malt Quality and Extract Characteristics

The effect of a high temperature‐high humidity treatment (HT‐HHT) of germinated unkilned barley on malt quality and extract characteristics was studied. Two samples of six‐row barley were steeped to 42% moisture and germinated, with and without gibberellic acid, at 15°C for 5 days. The germinated barley was placed in a high humidity (75–80%) atmosphere maintained at 45, 55, and 65°C, respectively. For each temperature, treatments were carried out for 30, 60 and 90 min, respectively. At 45°C for 30–60 min, the malts developed high diastatic power and proteolytic activity. The high values for cold water extract and reducing sugars in the extracts indicated extensive amylolysis of starch granules during HT‐HHT of the germinated barley at 55–65°C. The worts were light in colour, with a pH of 5.3–5.8 and titratable acidity was in the range of 0.09‐0.23%. A consistent increase in soluble nitrogen and Kolbach index was observed in the malts treated at 45–55°C for 30–90 min. Free α‐amino nitrogen of the malts was in the desirable range of 120–150 mg L^?1. Therefore, HT‐HHT can be useful for improving malt modification and wort characteristics and to shorten the germination time for malts from poor quality barley.     

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.     

Analytica‐EBC — Precision Values of Wort Analyses

In Analytica‐EBC (1) method 8.3: Specific Gravity of Wort by Density Meter, method 8.4: Viscosity of Wort: Glass Capillary Viscometer (IM), method 8.5: Colour of Wort: Spectrophotometric Method (IM), method 8.7: Fermentable Carbohydrates in Wort by HPLC (IM), method 8.8: Bitterness of Wort (IM), method 8.9.1: Total Nitrogen in Wort: Kjeldahl Method and method 8.11: Zinc in Wort by Atomic Absorption Spectrophotometry (IM) are described, but repeatability (r₉₅) and reproducibility (R₉₅) values are missing. These methods have been collaboratively tested by members of the Analysis Committee of the European Brewery Convention in 1999 to obtain the corresponding precision data. In method 8.12: Total Polyphenols in Wort by Spectrophotometry the precision values are missing as well, but because of testing a new ammonium ferric citrate reagent the data have been postponed. The worts analyzed had extract contents of ca 18°P (% m/m), 14°P, 12°P, 10°P and 8°P respectively. The precision values are listed below (n = number of participating laboratories, m = mean value).     

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 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.     

DETERMINATION OF ALUMINIUM IN BEER BY GF-AAS

A method for the determination of aluminum in beer, has been collaboratively tested. The method tested relies on atomic absorption spectrometry with atomization in a graphite furnace. Five pairs of beers, with concentrations ranging from 96 to 1000 μg/litre, were analysed by eleven laboratories. The repeatability (r₉₅) values ranged from 10 to 69 μg/l, and the reproducibility (R₉₅) values ranged from 70 to 465 μg/l,. A second collaborative trial with a slightly different method protocol gave no improvement. Due to the high reproducibility values the method was not adopted for inclusion in Analytica-EBC.     

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 .     

Starch properties as affected by sorghum grain chemistry

To determine the relationship between sorghum grain polyphenol content, grain structure, and starch properties, starch was isolated from 10 sorghum varieties using an alkali steep and wet‐milling procedure. SV2, a tannin‐free variety with white pericarp, gave a white starch. Varieties having red or white pericarp and higher polyphenol levels gave pink starches. Hunter colour values (L, a, b) of starches were not correlated with grain polyphenol content. Grain appearance in terms of pericarp colour, or presence or absence of pigmented testa, did not relate to the intense pink colouration of sorghum starches. Starch amylose content was significantly negatively correlated (r = −0.88, p < 0.001) to grain floury endosperm texture. Sorghum starches had higher peak viscosity (PV) in pasting than commercial maize starch. The time taken to reach peak viscosity from the initial viscosity rise was less for sorghum starches than maize starch. However, sorghum starches had a higher rate of shear thinning (R_st) than maize starch. There was a significant positive correlation between grain polyphenol content and starch PV (r = 0.75, p < 0.05). Starch gel hardness was negatively correlated to pasting properties of R_st and paste breakdown (r = −0.78 and −0.77 respectively) at p < 0.01. Peak gelatinisation temperature (T_p) occurred over a narrow range from 66 to 69 °C. T_p was negatively correlated to the floury endosperm portion of the grain (r = −0.77) at p < 0.01. It is concluded that sorghum grain polyphenol content and grain characteristics influence its starch properties. © 2000 Society of Chemical Industry     

The influence of temperature and grain moisture content on the intrinsic rate of increase of Sitophilus oryzae (L.) (Coleoptera: Curculionidae)

The intrinsic weekly rates of increase (r_m) of Sitophilus oryzae (L.) living in wheat of 14 or 11.2% moisture content (m.c.) at 15, 18 and 21°C were determined both by using schedules of fertility, i.e. observed numbers of adult offspring produced by cohorts of young weevils, and schedules of adult survivorship, age-specific fecundity, i.e. egg production, and estimates of the proportion of immature stages surviving to adulthood. In wheat of 14% m.c., with the former, r_m ranged from 0.0718 at 15°C to 0.4498 at 21°C and, with the latter, from 0.0737 at 15°C to 0.4154 at 21°C. Both sets of values revealed an interaction between the effects of temperature and m.c. in that corresponding values in wheat of 11.2% m.c. ranged from 0.0383 to 0.3677 with the former, and from 0.0348 to 0.3025 with the latter.Additional experiments showed that values of r_m derived from survivorship and fecundity schedules for S. oryzae in wheat of 12.5% m.c. ranged from 0.0560 at 15°C to 0.3378 at 21°C. No eggs were laid at 15°C in wheat of 10.3% m.c. By contrast, oviposition, but not development, was observed at 11°C in wheat of 14% m.c.Possible causes for the differences between the values of r_m provided by the two methods used in the present study and the literature are examined.     

Impact of Dark Specialty Malts on Extract Composition and Wort Fermentation

Dark specialty malts are important ingredients for the production of several beer styles. These malts not only impart colour, flavour and antioxidative activity to wort and beer, they also affect the course of wort fermentations and the production of flavour‐active yeast metabolites. The application of considerable levels of dark malt was found to lower the attenuation, mainly as a result of lower levels of fermentable sugars and amino acids in dark wort samples. In fact, from the darkest caramel malts and from roasted malts, practically no fermentable material can be hydrolysed by pilsner malt enzymes during mashing. Compared to wort brewed with 50% pilsner malt and 50% dark caramel malt or roasted malt, wort brewed with 100% pilsner malt contained nearly twice as much fermentable sugars and amino acids. Reduced levels of yeast nutrients also lowered the fermentation rate, ranging from 1.7°P/day for the reference pilsner wort of 9 EBC to 1.1°P/day for the darkest wort (890 EBC units), brewed with 50% roasted malt. This additionally indicates that lower attenuation values for dark wort are partially due to the inhibitory effects of Maillard compounds on yeast metabolism. The application of dark caramel or roasted malts further led to elevated levels of the vicinal diketones diacetyl and 2,3‐pentanedione. Only large levels of roasted malt gave rise to two significant diacetyl peaks during fermentation. The level of ethyl acetate in beer was inversely related to colour, whereas the level of isoamyl acetate appeared to be affected by the use of roasted malt. With large levels of this malt type, negligible isoamyl acetate was generated during fermentation.     

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.     

Treatment of wx corn starch dispersions in a microwave reactor and their hydrodynamic properties determined using asymmetrical flow field‐flow fractionation

Hydrodynamic properties of aqueous wx corn starch (native, un‐pregelatinised) dispersions treated in a dedicated single‐mode microwave reactor at temperatures ranging from 180 to 210°C were determined using asymmetrical flow field‐flow fractionation coupled with an RI detector. The dedicated microwave reactor enabled the fine control and monitoring of heating parameters (especially temperature) during the treatment. The translational diffusion co‐efficient and hydrodynamic radii (R_h) values determined for wx corn starch treated at 180 and 200°C indicate that the majority of the material (∼98%) consisted of highly mobile, small and compact molecules/particles, with R_h values ranging from 10 to 90 nm, while the remaining ∼2% of the material consisted of considerably larger molecules/particles R_h values ranging from ∼100 to ∼200 nm). Degradation of wx corn starch was observed at 210°C.