2002 Mathematics Subject Classification: 62P30, 62P10.The colloidal stability is very important part of the total beer quality. The stabilized beers have to have a long shelf-life. Determination of some haze forming complexes could be very useful for prediction of beer colloidal stability. We study the repeatability and reproducibility of a method for determination of some haze forming complexes in beer. The method was tested in 10 laboratories. All of theme analyzed the same beer samples and carried out two measurements for each. Statistical evaluation of results was according ISO 5725 and previous experience. The applied ISO 5725 statistical analyzes ensured high quality and possibility of international recognition of the measurement method.Partially supported by Mathind IST-2000-26015 and by Pro-enbis GTC1-2001-43031

Batchvarov, V.

Christozov, D.

Marinova, G.

Mateev, P.

Bulgarian Digital Mathematics Library at IMI-BAS

Pliska Stud. Math. Bulgar. 14 (2003), 37–44STUDIA MATHEMATICABULGARICAAN APPLICATION OF ISO 5725 IN BREWING INDUSTRYV. Batchvarov, G. Marinova, P. Mateev, D. ChristozovThe colloidal stability is very important part of the total beer quality.The stabilized beers have to have a long shelf-life. Determination of somehaze forming complexes could be very useful for prediction of beer colloidalstability.We study the repeatability and reproducibility of a method for determi-nation of some haze forming complexes in beer. The method was tested in 10laboratories. All of theme analyzed the same beer samples and carried outtwo measurements for each. Statistical evaluation of results was accordingISO 5725 and previous experience. The applied ISO 5725 statistical ana-lyzes ensured high quality and possibility of international recognition of themeasurement method.1. IntroductionThe most important property of a measurement method is its accuracy. Evalua-tion the accuracy of the results of measurements and evaluation of the influence,which external factors have on the accuracy, are very important stages in devel-oping and implementing methods for assessment beer quality. Among the majorcriteria for evaluation of beer quality are considered:– Colloidal stability - long shelf-life;– Haze forming complexes;2002 Mathematics Subject Classification: 62P30, 62P10Key words: beer, alcohol chill haze, Test Chapon, colloidal stability, ISO 5725, Mandel‘sstatisticsPartially supported by Mathind IST-2000-26015 and by Pro-enbis GTC1-2001-43031.38 Batchvarov, V. , G. Marinova , P. Mateev , D. Christozov– Prediction stability.The objectives of this paper are to present the evaluating procedure of anadjusted method to measure colloidal stability based on alcohol chill haze test[4]. The evaluation of method’s usability follows the requirements of the standardISO 5725 [8].2. The measurement methodDetermination of alcohol chill haze in beer was introduced by Chapon and Che-mardin [5]. The specially constructed apparatus consists of refrigerated neph-elometer measuring the scattered light at 90o (Fig. 1) and plotter for registrationof the nephelometric curves.Figure 1: Principle of nephelometric mesurement: refrigerating and measuringthe scattered light.The effect of 1% alcohol addition to the beer is approximately equals to 1oCtemperature decreasing. In the temperature interval -4oC to -8oC, 1oC temper-ature decreasing of beer is approximately equals to 1.5 EBC haze increasing.Chapon‘s nephelometer is not able to measure more than 20 EBC units haze.An application of ISO 5725 in Brewing Industry 39There are modified versions of the alcohol chill haze test (see [1], [2], [3],[4], [5], [6], and [7]), which use different alcohol doses (reagent/beer ratio 3 to6%), different temperatures (-4oC to -8oC) and different time of assay (40 to 100minutes) .Table 1 shows parameters of three methods for determination of beer alcoholchill haze.Conditions Chapon ([4], [5], [6]) Batchvarov et al.([2], [3]) IOB ([7])Reagent C2H5OH C2H5OH C2H5OHBeer volume,ml 4 200 250Reagent volume, ml 0.24 6 15Ratio reagent/beer, % 6 3 6Temperature, oC -8 -5 -5Time of assay, min. 40 40 60Table 1: Determination of alcohol chill haze in beer three methods.The Institute of Brewing (IOB) method [7] is not applicable for some nonstabilized and normally stabilized beers (beers, with final turbidity greater than10 - 12 EBC units). The method of consideration (Batchvarov et al. [3]) ischaracterized by 6 ml C2H5OH is added to 200 ml of degassed beer. The beersamples stay at -5oC for 40 minutes. The amount of alcohol chill haze is measuredas an increase of the haze of the beer.3. ExperimentFour stabilized and pasteurized beer samples with different alcohol chill hazelevels were analyzed by 10 independent laboratories. Each laboratory processtwice every sample according to the modified Chapon‘s alcohol chill haze test [3]and return the two measurements for each of the four beers. These results wereobtained using nephelometers (haze meters) with 90o measuring angle, but withcertain differences in measuring wavelength and geometry of the optical systems.Statistical evaluation of results was performed according to ISO 5725 [8]. Ourprevious experience [9] in implementing this standard was instrumental in adop-tion of the data processing algorithms. The standard uses criteria ”repeatability”(within-laboratory-variance) and ”reproducibility” (total variance) to measurethe quality of the given method. The term ”level” corresponds to brand of beerused in the experiment. Our experiment explores four brands of beers, each ofthe ten laboratories made 2 independent measurements for each beer. Or, in the40 Batchvarov, V. , G. Marinova , P. Mateev , D. ChristozovISO 5728 terminology, we have an experiment of ten laboratories, four levels,with two observation in a cell. The data collected during the experiment arepresented in Table 2.Laboratory Beer 1 Beer 2 Beer 3 Beer 41 0.43 1.40 5.15 9.181 0.45 1.35 5.03 9.072 0.40 1.53 4.65 8.642 0.38 1.47 4.57 8.483 0.66 1.62 5.09 8.813 0.58 1.82 5.86 8.884 0.43 1.69 6.60 9.744 0.50 1.73 6.73 9.675 0.38 1.80 5.76 9.655 0.42 1.75 7.02 9.486 0.39 1.20 3.92 7.606 0.32 1.63 4.15 7.347 0.58 1.30 4.30 7.417 0.63 1.39 4.18 7.758 0.37 1.41 5.15 9.068 0.40 1.17 4.75 9.089 0.45 1.60 3.09 6.379 0.45 1.50 2.60 5.9510 0.54 1.74 5.05 8.9010 0.46 1.69 5.33 8.70Table 2: Results: Alcohol chill haze in Beer (EBC units).4. Results and DiscussionThe performed data processing was divided into three phases:1. Outliers and strugglers2. Precision3. RelationshipMandel‘s k and Mandel‘s h statistics to identify and exclude outliers are givenin Fig. 2 and Fig. 3. Two outliers (laboratory 5 on level 3 and laboratory 6 onlevel 2) and one straggler (laboratory 9 on level 3) were detected by k statistics.The h statistic did not show outliers and stragglers. The detected outliers wereexcluded from the further analysis.An application of ISO 5725 in Brewing Industry 41Figure 2: Mandel‘s within laboratory consistency statistic, k. The critical valuefor 5% (1%) confidence is 1.90 (2.32) when n = 10 and 1.90 (2.29) if n = 9.Figure 3: Mandel‘s between laboratory consistency statistic, h. The critical valuefor 5% (1%) confidence is 1.80 (2.22) when n = 10 and 1.80 (2.18) if n = 9.42 Batchvarov, V. , G. Marinova , P. Mateev , D. ChristozovThe data for the precision of the measurement method are summarized inTable 3. It includes means, standard deviations (within, and between laboratory),coefficients of repeatability and reproducibility, and coefficients of variation (CV)of them.Sample Beer 1 Beer 2 Beer 3 Beer 4Number of laboratory 10 9 9 10Grand mean (m) 0.461 1.553 4.789 8.488Repeatability standard deviation (Sr) 0.038 0.084 0.256 0.154Reproducibility standard deviation (SR) 0.094 0.195 1.073 1.106Repeatability (r95) 0.105 0.236 0.716 0.432Reproducibility (R95) 0.264 0.545 3.004 3.096CV of repeatability (CVSr) 8.17 5.44 5.34 1.82CV of reproducibility (CVSR) 20.49 12.54 22.41 13.03Table 3: Summary of the precision data (calculated from data of table 2).The relationships are represented by the dependencies of repeatability andreproducibility standard deviations on the mean value. Three models of relation-ship are tested. Results are given in Table 4 and Table 5 correspondingly.Multiple R Relationship0.331 Sr = 0.027m0.632 Sr = 0.070 + 0.017m0.907 log Sr = −2.734 + 0.580mTable 4: Relationship between repeatability standard deviation (Sr) and themean (m).Multiple R Relationship0.909 SR = 0.152m0.917 SR = 0.086 + 0.139m0.972 log SR = −1.744 + 0.935mTable 5: Relationship between reproducibility standard deviation (SR) and themean (m).In the both cases the logarithmic model were preferred.An application of ISO 5725 in Brewing Industry 435. ConclusionsThe considered method for determination of alcohol chill haze (modified Chapontest) demonstrates acceptable repeatability and reproducibility.The method canbe used to monitor the effectiveness of stabilization treatment and for predictionof the shelf-life of beer. A beer with a relatively low alcohol chill haze is expectedto have a better colloidal stability than a beer with relatively greater one.Application of the ISO 5725 statistical analyzes procedure ensured the inter-national recognition of the above considerations.REFERE NCES[1] G.Annemuller, G. Heidrich. Untersuchungen zur kolloidalen stabil-itat von bieren und den moglichkeit ihrer effectiven vorausbestimmung,Lebensmittelindustrie, 26, 3 (1979), 119–124.[2] V.Batchvarov, B. Abadjiev, S. Kozarov. Termostatical device forlow temperature investigations of liquid foods, BG Patent 40103 (1985).[3] V.Batchvarov, G. Marinova, B. Abadjev, S. Kozarov. Low tem-perature tests for prediction of beer colloidal stability. In: Proceedingsof the National Conference ”Physical methods for food control”, Plovdiv,(1985), 51.[4] V.Batchvarov, L. Chapon. Vorausbestimmung der kolloiden Bierhalt-barkeit, Monatsschrift fur Brauwissenschaft, 38, 8 (1985), 331-342.[5] L.Chapon, M. Chemardin. Etude sur les trouble au froid, In: Proceed-ings of the European Brewery Convention, (1967), 389–405.[6] L.Chapon. Nephelometry as a method for studying the relations betweenpolyphenols and proteins, J. of the Institute of Brewing, 99 1/2, (1993),49–56.[7] Institute of Brewing – Methods of analysis. Method 9.38 Alcohol ChillHaze, (1997), 1–2 .[8] International Standard Organization, ISO 5725-2. Basic method for deter-mination of repeatability and reproducibility of a standard measurementmethod, 1994.44 Batchvarov, V. , G. Marinova , P. Mateev , D. Christozov[9] E.Kamburova, D. Christozov. Assessment of and Comparison be-tween Bulgarian and International Standards for Quality Control of Eval-uation of Elements‘ Composition of Geological Samples, Analytical Labo-ratory 4 (1997), 205–221.Valentin BatchvarovBrewing Technology DepartmentInstitute of Cryobiology and Food Technologies134, Tzar Boris III blvd, 1618 Sofiae-mail: ibhi@prolink.bgGabriela MarinovaBrewing Technology DepartmentInstitute of Cryobiology and Food Technologies134, Tzar Boris III blvd, 1618 Sofiae-mail: ibhi@prolink.bgPlamen MateevInstitute of Mathematics and InformaticsBulgarian Academy of SciencesAcad. G. Bontchev str., bl.81113 Sofia, Bulgariae-mail: pmath@math.bas.bgDimitar ChristozovAmerican University in BulgariaBlagoevgrad 2700e-mail: dgc@aubg.bg

An Application of ISO 5725 in Brewing Industry

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An Application of ISO 5725 in Brewing Industry

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