Prediction of Malt Sugar Content in Converted Mash

Prediction of malt sugar content in converted mashDipl.-Ing. Hans Scheuren*, Dipl.-Ing. Johannes Tippmann, Dr.-Ing. Jens Voigt, Univ.-Prof. Dr.-Ing. Karl SommerTechnische Universität MünchenLehrstuhl für Maschinen- und ApparatekundeAm Forum 285354 Freising - Weihenstephan, Germanyphone: +49 (0) 8161 71 4237, fax: +49 (0) 8161 71 4242, e-mail: H.Scheuren@wzw.tum.deAbstractThe central process of beer production is the mashing process. In this step, ground malt and water aremixed and a suspension is produced. By using special time and temperature profiles this mash istransformed to a solution which is called wort. This wort is the essential basic for the quality for thedownstream product beer.For every brewer this process has to be of highest interest, because the quality of the final product beeris strongly influenced by the mashing step which is characterised by different enzymatic reactions. Themost important one is the starch degradation and along with it the sugar profile. Working amylolyticenzymes and their conditions are well known and can be found in literature. In spite of this the kineticsof the whole process, which consists of gelatinization and saccharification, are difficult to describe.The missing understanding results in a lack of control which can be seen in the standard, safetymashingprogrammes. To predict the content of sugar in wort there are different mathematical models.Examples are the models of Marc (4), Koljonen (3), Einsiedler (1) and Muller (6). They all can befound in literature and provide good accuracy. Object of this work is an improvement of themathematical model of Einsiedler.Key WordsMalt, Mashing, Milling, Wort, BrewingIntroductionFor describing the kinetics of mashing in most calculation models, common differential equations areused. They include the mass balance, the temperature dependence of the different reaction steps andespecially the mass transport of the most important enzymes. Concerning the last parameters, themovement of molecules of water within and outside of starch agglomerates has to be modelled. In anagglomerate of starch particles, movement is created only by diffusion and not by convection. Thusfor calculating the mass transport of an enzyme like Alpha-amylase its diffusive attributes in waterinfluenced by mashing conditions must be researched.Experimental1

The diffusion of a molecule is described by its diffusion coefficient. This parameter is characteristicfor a molecule or a substance in a surrounding medium and is influenced by factors like the size of themolecule. Another important variable consists in the temperature dependence of diffusion. In the caseof mashing, varying temperatures during the individual mashing programmes have to be considered.In the work of Einsiedler the mass transport caused by diffusion is affected by an additional parameter.Mashes brewed by differently milled malt result in varying wort qualities (1,5). That means thatchanges in the particle size distribution influence the mashing process. Varying sizes of the starchgranules caused by natural fluctuations of the resource malt and its splitting or agglomeration causedby malting have an additional influence on the mass transport of water in starch particles and theenzymes inside.As a consequence the parameterisation of a mathematical model which is only adapted to mashes isstrongly influenced by the milling, malting and barley conditions. The resulting diffusive properties ofAlpha-amylase, which can be calculated by the mass transport, are strongly inconsistent.Therefore a new version of a calculation model by Einsiedler is presented, which is matched to purecomponent systems, just consisting of water, barley flour and Alpha-amylase. Furthermore the flour isagglomerated by the method “Concentrated Powder Form” (CPF) (2) to get different particle sizedistributions simulating varying malt qualities and milling conditions. This procedure means thepossibility to detect the relation between mass transport, diffusion and particle size distribution.One flour is agglomerated with 8%, another one is agglomerated with 15% water. The original and theagglomerated ones were dried for 24 hours at 65°C to the same low moisture of 1-3%. The followingfigure shows particles of flour which were agglomerated with 8 and 15 % water. The structures of theparticles which are caused by the small starch granules can be seen in these pictures.300 µm80 µmFigure 1: Agglomerated flour (15% water)Figure 2: Agglomerated flour (8% water)2

By using an isothermal mashing programme within a typical temperature range (55-75°C) the kineticsof the creation of extract and sugars were investigated, the viscosity and variances in the viscosityconcerning changes in the particle size distribution were also determined. Taking all this informationinto account the mass transport of the enzyme Alpha-amylase can be described and calculated forvarying mashing conditions.The model used is based on the work of Einsiedler which is mathematically based on the work ofKettunen et al. To describe the whole process of starch degradation and of saccharification 16differential equations are introduced.The activity of the Alpha-amylase is expressed by four equations. Two equations contain variablesconcerning the concentration of enzyme in grist and water, the ratio grist to water volume and thediffusive constant. This parameter is calculated with a third equation which describes the temperaturedependency of the diffusion. A reaction constant for the enzyme inactivation is calculated with thefourth equation by Arrhenius law. Therefore the activation energy has to be investigated.The activity of the Beta-Amylase is expressed by three equations. Two equations are similar to Alphaamylase.The diffusion is seen as independent from temperature and therefore it is a constant. Thethird equation describes the inactivation of the Beta-Amylase.These formulae are components of the following ones which include the conversion of starch in sugar(e.g. glucose, maltose, maltotriose) and dextrines. Important variables are the concentration ofenzymes, of starch and their different factors describing the reaction velocity and quality.Figure 3 shows the processes included in the model.Figure 3: Schematic representation of mashing processThe diffusion of Alpha-amylase is marked by rings. The quality of the saccharification is dependent onthe cleavage of starch and its degradation by Alpha-amylase. It is obvious that the mass transport andthe reaction of this enzyme are the basic steps for the subsequent enzymatic reactions.More information concerning the model can be found in literature (2, 3).3

The aim of this work is to research the influence of the particle size distribution on the mass transportof Alpha-amylase and the mashing success. The first result can be seen in the following figures.Particle size distribution at the beginning of mashing (75°C)1particle size distribution [-]0,90,80,70,60,50,40,3flourflour agglomerated0,20,100 50 100 150 200 250 300 350 400 450 500particle size [µm]Figure 4: comparison of the particle size distribution of flour and flour agglomerated (15%) at thebeginning of mashingParticle size distribution at the end of mashing (75°C)1,0particle size distribution [-]0,90,80,70,60,50,40,3flourflour agglomerated0,20,10,00 50 100 150 200 250 300 350 400 450 500particle size [µm]Figure 5: comparison of the particle size distribution of flour and flour agglomerated (15%) at the end ofmashing4

Figure 4 contains the particle size distribution of flour and flour agglomerated by CPF with 15% waterat the beginning of the mashing process. Figure 5 describes the particle size distribution of flour andagglomerated flour at the end of the experiments. Both experiments are performed three times asisothermal mashes at a temperature of 75°C.The development in the particle size distribution is obvious. Furthermore the differences between bothflours are obvious too. The values of the different x 50 - factors at the beginning and at the end of themashing experiment confirm this comparison.x 50 (flour) x 50 (flour agglomerated)start of mash (40,5 ± 0,72) µm (55,01 ± 7,04) µmend of mash (85,42 ± 6,70) µm (205,26 ± 43,14) µmTable I: Comparison of x 50 -valuesThese results are used to calculate the mass transport of Alpha-amylase considering the differentdiffusion constants for 55, 65 and 75°C and the particle size distribution. The mathematical modelused is parameterised with these values. Consecutively one result concerning the creation of extract ispresented. Figure 5 contains an experiment in laboratory scale concerning malt milled with mill gap of0.2 mm.Figure 5: Comparison of prediction and experiment with malt milled (gap 0.2 mm)The calculation curve is conforming to the experimental value and its confidence belt. The diagramshows the quality of the prediction of the extract at the end of the mashing process.5

DiscussionThe aim of this work is to show the possibility of the prediction of the content of sugars and dextrinesat the end of the mashing process using a calculation method. Therefore a new version of the model byEinsiedler is presented, which is matched to pure component systems and adapted to mashes. By thismethod the influence of the particle size distribution on the starch particles can be described.The new parameterised model is tested on a laboratory scale and provides good predictability. Toexpand and to optimise the predicted results it is planned to research the kinetics of the mass transportof the Beta-amylase. Furthermore the kinetics of decomposition of Beta-glucan will be researched.These results will help to improve the accuracy and the adaptability. By this method the practical useof the described prediction method will be increased and the model could become a possibility toimprove the standard mashing programmes.AcknowledgementsThe Authors would like to thank Novozymes, Krogshoejvej, Denmark for their friendly support.References(1) Einsiedler, F., Schwill-Miedaner, A., Sommer, K., Hämäläinen, J Reaction kinetic studies onthe modelling of starch hydrolyses during mashing. Brauwelt, 1997, 137, 1598-1603.(2) Grüner, S., Otto, F., Weidenreich, B., Chemie Ingenieur Technik, 75, 2003, 690-693.(3) Koljonen, T., Hämäläinen, J. Sjöholm K., Pietilä, K., A Model fort he Prediction ofFermentable Sugar Concentrations During Mashing. J Food Engineering, 1995, 29,185-200.(4) Marc, A., Engasser, J.M., Moll, M., A Kinetic Model of Starch Hydrolysis by α- and β-Amylase during Mashing. Biotechnol Bioeng, 1983, 25, 481-496.(5) Mousia, Z., Balkin, R.C., Pandiella, S.S., Webb, C., Te effect of milling parameters on starchhydrolysis of milled malt in the brewing process, Process Biochemistry, 39, 2004, 2213-2219.(6) Muller, R. A mathematical model of the formation of fermentable sugars from starchhydolysis during high-temperature mashing, Enzyme and Microbial Technology, 2000, 27,337-344.6