RVA.pdf

8/14/2019 RVA.pdf

1/11

VOL. 111, NO. 2, 2005 165

Application of the Rapid Visco Analyser as a

Rheological Tool for the Characterisation

of Mash Viscosity as Affected by the

Level of Barley Adjunct

Declan L. Goode1, Eric A. Wiltschko1, Helge M. Ulmer1and Elke K. Arendt2,3

ABSTRACT

J. Inst. Brew. 111(2), 165175, 2005

The application of the Rapid Visco Analyser (RVA) as a labora-tory scale rheological tool for the characterisation of mash vis-cosity is the subject of this study. Studies were conducted tosimulate an industrial mashing process, taking into account tem-

perature/ time, grist loads, adjunct amounts and enzyme levels.The RVA was used to characterise the effects of different ratiosof malt :barley adjunct. The method was found to have the abil-ity of not only detecting the major viscosity changes which oc-cur during starch gelatinisation/liquefaction processes, but alsothe minor viscosity changes which were found to occur duringthe proteolytic and saccharification steps. Clear correlationswere found between the level of barley adjunct and the outputrheological data points of the peak viscosity at 50C (PV50, R2= 0.9931), the rate of viscosity breakdown at 50C (BR50, R 2=0.9522), the peak viscosity prior to gelatinisation (PVG, R2 =0.9988), the area recorded under the gelatinisation curve (PGA,R2= 0.9928) and the peak viscosity breakdown rate (VBR, R 2=0.9783). The developed RVA rheological method is a useful toolfor characterising grain quality (adjunct level) with regard to

macromolecular viscosity compounds and the grains endoge-nous enzymatic capabilities.

Key words:Barley adjunct, mashing, rheology, viscosity.

INTRODUCTION

Different instruments which operate on the basis ofrheological viscosimetric measurements have been pro-posed for possible applications in the determination ofgrain quality in the brewing industry. These have includedthe amylograph, which has been used to assess the qual-ity and degree of modification of a finely ground maltsample20,21,27,28, the falling number apparatus, which hasbeen used to determine, starch degradation during germi-

nation22, the rapid visco-analyser (RVA), which has beenused as a tool for monitoring the overall quality of malted

barley3,610 and wheat adjunct additions3, and the Rheo-swing RSD 1-1 which has been used to characterise thequality of malt26and to show correlations between labora-tory congress mashing results and rheological curves16.However, none of these methods have become widely usedfor analysis in the malting, brewing and distilling indus-

tries.The most recently developed rheological measurementsystem for grain characterisation was developed by thepresent authors1113. In that system a Bohlin CS-50 rheom-eter, together with a specially designed star-shaped paddlerotor was used. In comparison to the previously mentionedrheological methods, the Bohlin mash rheological methodwas designed to simulate more closely the operating con-ditions of an industrial mashing process by taking into ac-count temperature/time, grist loads, adjunct amounts andenzyme levels. Validation of the method was carried outby carrying out model studies using purified/non purifiedsubstrates and enzyme types and dosage levels of knownspecification13. The method was found to have the ability

of not only detecting the major viscosity changes whichoccur during starch gelatinisation/liquefaction processesbut also the minor viscosity changes which were found tooccur during the proteolytic and saccharifaction mashingsteps. In this method the effects on viscosity trends due tothe grains chemical constituents and its endogenous en-zyme components could be clearly visualised13. When themethod was applied to study the degree of grain modifica-tion, clear correlations were established between the rheo-logical data and the simulated degree of modification ofthe grist. This could then be related back to the endoge-nous enzymatic activities of the grains, together with theirlevels of under-hydrolysed grain components12.

The aim of the present study was to assess whether the

RVA is capable of determining a mash rheological profile.The RVA was used together with the previously developedmash rheological methods of Goode et al.1113 to assessthe impact that barley adjunct addition has on rheologicalprofiles obtained during mashing.

MATERIALS AND METHODS

Barley

Unmalted and malted barley (Optic variety) (Table I)were obtained from The Malting Company of Ireland

1 Department of Food and Nutritional Sciences, National Food Bio-

technology Centre, National University of Ireland, University Col-

lege Cork, Ireland.2 Department of Food and Nutritional Sciences, National University

of Ireland, University College Cork, Ireland.3 Corresponding author. E-mail: [email protected]

Publication no. G-2005-0816-281

2005 The Institute of Brewing & Distilling

8/14/2019 RVA.pdf

2/11

166 JOURNAL OF THE INSTITUTE OF BREWING

(Cork, Ireland). Distilled water was used as the mashingliquor.

Grain analysis/enzyme activity determination

The malted barley and unmalted barley grains werecharacterised using the standard methods of the EuropeanBrewery Convention (EBC)5 (Table I). The total starchcontent of the grain was measured using the MegazymeTotal Starch Assay Kit (International Association for Ce-

real Science and Technology (ICC) method 168 17) (Bray,Co. Wicklow, Ireland).

Enzyme activity of the grain (-amylase activity, -amylase activity, -glucanase activity) was determined us-ing the following methods.

The -amylase activity was measured using the Mega-zyme -amylase assay procedure (ceralpha method) usingamylase HR reagent (ICC method 303 17). One unit of ac-tivity is defined as the amount of enzyme, that is required,in the presence of excess thermostable -glucosidase, torelease one micromole of p-nitrophenol from BPNPG7(non-reducing-end blocked p-nitrophenyl maltoheptaos-ide) in one minute under the defined assay conditions. It istermed a Ceralpha Unit.

The -amylase activity was measured using the Mega-zyme -amylase assay procedure (betamyl method, RACIstandard method). One unit of activity is defined as theamount of enzyme, that is required, in the presence of ex-cess -glucosidase, to release one micromole of -nitro-phenol from PNPG5 (p-nitrophenyl--D-maltopentaose)in one minute under the defined assay conditions. It istermed a Betamyl Unit.

The -glucanase activity was measured using theMegazyme -glucanase assay procedure (azo-barley glu-can (dyed substrate) method, RACI standard method).One unit of activity is equivalent to one International Unitof enzyme activity. This equals one mole of glucose re-ducing sugar equivalent released per minute at 30C and

pH 4.6.

Rapid Visco Analyser (RVA)

The RVA (Fig. 1) was developed by the Bread Re-search Institute of Australia, in collaboration with theWheat Research Unit of CSIRO9. In this study, all rheo-logical investigations were carried out using the RVASuper3 (Newport Scientific, Warriewood, Australia). Theshear stress was measured with appliance of a constantshear rate. The RVA is a controlled shear rate instrument,in that it applies a constant shear rate (rpm) and then mea-sures the resultant torque (force, shear stress). Torque anddisplacement are then converted to rheological format bymeans of the measuring system constants. Data can be

produced in both a tabular and graphical format.

Measuring system

The RVA is a Searle type viscometer, with a stationarybowl and a combined stirring and sensing element sus-pended concentrically. Non-laminar or turbulent flow athigh speeds prohibits absolute viscosity measurements, aneffect which is exacerbated by the mixing-paddle designof the sensor element. However, it has been shown to cor-relate quite closely with similar viscosity data, determinedwith the amylograph9. The RVA system, consists of a one-

way plastic stirrer and aluminium sample canister. Before

initiating a sample measurement, the plastic stirrer wasplaced in the torque measuring arm of the RVA and zeroedat 160 rpm against air. After pre-weighing the requiredwater and sample weights into the aluminium sample can-isters, the plastic stirrer was placed in the sample cup andjogged up and down for a few seconds to ensure samplemixing and to prevent sample clumping. The sample can-ister was then immediately placed in the hot block of theRVA, the plastic stirrer was re-attached to the instrumentand the pre-programmed rheological profile was initiated.For all samples, an initial 10 s period of mixing at a con-stant shear rate of 960 rpm was carried out. For the re-mainder of the rheological measurement duration a con-stant shear rate of 160 rpm was applied. The shear stress

was measured under a constant shear rate. In all investiga-tions measurement points were taken every 0.5 s.

Temperature profile

In all experiments the temperature profile during theviscosity-measuring phase was kept constant. The tem-perature profile was as follows: 50C 30 min, 62C 40min, 72C 20 min and 78C 5 min. The heating ratewas 1C/min. The total time of mashing was 123 min.This temperature profile was chosen to simulate an up-ward infusion-mashing programme as is typically usedduring a brewery mashing programme.

Experimental design

Mash compositions consisting of unmalted barley (wetweight) at levels of 0, 20, 40, 60, 80, 85, 90, 95 and 100%together with malted barley (wet weight) were subjectedto rheological measurement. Unmalted and malted barleywere milled using a Bhler Miag laboratory scale discmill (Bhler GmbH, Braunschweig, Germany) set at afine grind setting of 0.20 mm. All samples were milled onthe same day as the analysis was carried out. In all experi-ments 20.160 g 0.001 g of distilled water (50C) wasweighed into the measuring cup. The sample (7.840 g 0.001 g (dry wt)) was then added to give a liquor to grist

Table I.Specifications of malt and barley used in the study.

Malted barley Unmalted barley

Variety Optic OpticHarvest Ireland 2002 Ireland 2002Moisture (%) 4.01 0.053 12.61 0.039Nitrogen (%) 1.400 0.036 1.511 0.014Total soluble nitrogen (%) 0.058 0.002 n.d.Free amino nitrogen (mg/ l) 107.73 1.96 n.d.Total starch (% wet) n.a. 70.275 0.346-Glucan (%) 0.126 0.005 3.35 0.042

Extract recovery (%) 79.97 0.058 n.d.pH 6.00 0.005 n.d.Colour (EBC) 6.40 0.092 n.d.Viscosity (mPas) 1.60 0.021 n.d.Filterability Normal n.d.Apparent fermentability 82.267 0.24 n.d.-Amylase (ceralpha units/g

of wet grain) 91.3 1.92 0.067 0.003-Amylase (betamyl units/ g

of wet grain) 514.02 4.22 644.76 35.46-Glucanase (glucanase units/g

of dry grain) 267.15 9.10 21.05 0.66

n.d. = not determined.

8/14/2019 RVA.pdf

3/11

VOL. 111, NO. 2, 2005 167

ratio of 2.57:1. The sample was vigorously mixed withthe plastic stirrer to prevent clumping. Rheological mea-surements were immediately performed.

Interpretation of results

Rheological measurement data were stored in the dedi-cated RVA software programme Thermocline for Win-dows (Newport Scientific, Warriewood, Australia). Usingthis data recording and analysis system, rheological pro-files could be made. The profiles were then analysed andthe chosen results transferred to a Microsoft Excel work-sheet where further graphical representation and statisticalanalysis (ANOVA) of the data could be made.

Experimental procedure

Each experiment was repeated at least three times. The

tabular results quoted are the mean values of the repeatedexperiments together with standard deviations. The graph-ical results shown represent one sample measurement. Allviscosity data is given as mPa.s.

RESULTS AND DISCUSSION

It had been previously found with the Bohlin mashrheological method1113 that much valuable informationcould be extracted from rheological curves, when the en-dogenous grain enzyme systems were optimised. The four

main enzymatic reactions occurring during mashing arethe hydrolysis of proteins into peptides and free aminoacids, the degradation of -glucan chains, the hydrolysis

of pentosans (arabinan, xylans) and the breakdown ofgelatinised starch into both fermentable (glucose, maltoseand maltotriose) and unfermentable carbohydrates (DP 4)24. These conversions occur due to the action of proteo-lytic, pentosanolytic, glucanolytic and amylolytic enzymegroupings respectively26. To cover the optimal tempera-ture range of each enzyme group24, it was decided to simu-late an industrial time/temperature curve which wouldtypically be used in brew-house processing; a first rest(50C 30 min) for proteolysis, -glucan hydrolysis andpentosonase activity, a rest for the action of -amylase(62C 40 min), a rest for activity of -amylase (72C 20 min) followed by a temperature rest to promote en-zyme inactivation (78C 5 min). The heating rate be-

tween the holding times was 1C/min.

What was visualised during an RVA rheologicalanalysis?

A typical rheological profile (recorded during our tri-als) showing the recorded mashing conditions of time/temperature together with the chosen rheological measur-ing points is shown in Figure 2a. With reference to Goodeet al.12 it can be observed that curve shapes obtained inthese studies were similar to those obtained with the pre-viously developed Bohlin mash rheological method.

Fig. 1.Basic design and operation of the RVA mash rheological profiling system.

8/14/2019 RVA.pdf

4/11


The first step is mashing at 50C (Fig. 2b). At this mash-ing temperature the proteolytic enzymes (endo-proteinasesand exo-peptidases (carboxypeptidase, amino peptidaseand dipeptidase)) together with the endo--1,4-glucanaseand pentosanases are reported to be active 24. During thisstep, the viscosity increased from the initial viscosity at50C (SV50) to a maximum peak viscosity at 50C(PV50). It can be hypothesised that this first maximum ismost probably primarily associated with solubilization ofhigh molecular weight -glucans and mixing of the grain

with mashing liquor, resulting in hydration and swellingof the grain components. Dextrins, arabinoxylans and -glucans are known to contribute greatly to the viscosity ofwort and beer. Whilst dextrins are found to be the primarydeterminant of viscosity, the impact of both arabinoxylanand -glucan have been found to be more pronounced atlower concentrations25. The viscosity was then observedto decrease from PV50 to the viscosity recorded after 30min mashing at 50C (V50, 30). This decrease (happeningat a constant rate) is most likely due to the combined

Fig. 2a.Graphical representation of a typical rheological profile, showing the main parts of the pro-file that are expanded in Figs. 2b, c and d.

Fig. 2b.Rheological representation of the 50C 30 min mash stand, A = start viscosity at 50C(SV50), B = peak viscosity at 50C (PV50), C = viscosity after 30 min at 50C (V50, 30), D = rateof viscosity breakdown at 50C (BR50).

8/14/2019 RVA.pdf

5/11

VOL. 111, NO. 2, 2005 169

polymer degrading effects of glucanolytic, proteolytic andxylanolytic enzymes which have optimum temperatureactivities at circa 50C24.

With an increase in mash temperature from 50C to63C the viscosity was seen to increase rapidly (Fig. 2c).This temperature of viscosity increase is noted as beingthe point of the gelatinisation of the barley starch. Duringgelatinisation the starch granules take up warm water;

they soak and swell, causing a rapid increase in viscos-ity18. Because the starch granules swell due to water ab-sorption as they are heated, their volume fraction in-creases and reaches a maximum peak value (PVG). ThePVG viscosity parameter is reflective of the concentrationof barley starch and the level of amylase. Amylolytic en-zymes (- and -amylase and debranching enzyme) cantherefore act on this accessible starch substrate, thereby

Fig. 2c.Mash stands incorporating the temperatures for gelatinisation and liquefaction, E = gelati-nisation temperature (GT) and the time at GT (TG), F = peak viscosity after gelatinisation (PVG),

G = area under the gelatinisation peak with subtraction (PGAsubt), H = subtracted peak area, I =viscosity at breakdown (VB), J = rate of breakdown of viscosity from PVG to VB (VBR).

Fig. 2d.Mash stands at 62C 40 min, 72C 20 min and 78C 5 min, J = start viscosity at 62C(SV62), K = end viscosity at 62C (VE62), L = rate of viscosity breakdown at 62C (BR62), M =start viscosity at 72C (SV72), N = end viscosity at 72C (VE72), O = rate of viscosity breakdown

at 72C (BR72), P = end viscosity at 78C (VE78).

8/14/2019 RVA.pdf

6/11


decreasing the volume fraction of the granules in the sus-pension. Heating from 50 to 62C causes deactivation ofthe proteases and -glucanases24. The rate of viscositybreakdown (VBR) following formation of the PVG givesan indication of the digestibility of the gelatinised starch.

The mash was held at 62C (Fig. 2d). Further enzy-matic breakdown of the gelatinised starch is occurring dueto the combined action of the - and -amylases18. Due tothe action of -amylase, maltose production is continuing.The viscosity of the mash was thereby seen to reducefrom the viscosity recorded at the start of the 62C hold(SV62) to the viscosity recorded at the end of the 62Chold (VE62). This viscosity decrease can be attributedmainly to the endo-hydrolysing actions of the -amylase

and to a lesser extent to the exo-hydrolysing actions of -amylase. The mash temperature was then raised to 72C.At this temperature, it is reported that -amylase is lessactive24. Enzyme inactivation is an interaction betweentime and temperature. With an increase in time at tem-peratures 72C, -amylase is inactivated. The -amy-lases further break down the gelatinised starch and highmolecular weight dextrins into low molecular weight dex-trins and glucose18. The viscosity of the mash was ob-served to reduce from the viscosity recorded at the start ofthe 72C stand (SV72) to the viscosity recorded at the endof the 72C stand (VE72). The temperature was thenraised to 78C where enzyme inactivation is reported tooccur and the final viscosity at 78C was attained (VE78).

Application of the RVA rheological methodto assess the rheological behaviour of mashescontaining increasing levels of barley adjunct

In order to simulate the effects of different ratios ofmalt:barley adjunct, together with different quantities oftheir endogenous hydrolytic enzymes, the RVA rheologi-cal method was applied to mashing systems consisting ofunmalted barley together with malted barley at variousproportions.

Fig. 3 shows the effects of barley adjunct on the rheo-logical curve when the proportion of malted barley wasincreased in the mashing system. As the % malt was in-creased, the observed trend (Fig. 3, Table II) was a de-crease in SV50, PV50, V50,30 and BR50. As the percent-age malt was increased from 5100%, the PV50 was seento decrease from 1053 185 mPas to 199 10 mPas.Likewise, as the level of malt was increased, BR50 de-creased (18.65 4.42 mPas to 0.24 0.61 mPas) (TableII). The higher data values are most likely related to thehigher levels of undegraded macromolecular substances(i.e. -glucan, arabinoxylans and proteins) and loweramounts of endogenous enzymes at the higher levels ofbarley adjunct. Clear exponential correlations could be

made regarding, the % malt from 5% to 100%, with re-gard to PV50 (y = 1122.2e0.0182x, R2= 0.9931) and BR50(y = 31.159e0.0415x, R2= 0.9522). The results clearly con-fer with those previously shown in the Bohlin mash rheo-logical studies1113, in that the mash viscosity curve at50C was dependent on the level of added adjunct/under-modified grain (P < 0.001). This can be attributed mainlyto the higher levels of water-holding capacity of under de-graded macromolecular substances (i.e. -glucan, arabino-xylan(s) and proteins). It was also found that lack of -

Fig. 3.Rheological profiles of grist compositions representing various ratios of malt :barley adjunct overthe course of the 50C 30 min mash stand. (Top line = 5% malt; bottom line = 100% malt.)

Table II.Rheological data of mashes containing increasing levels of un-malted barley adjunct over the course of the 50C 30 min mash stand.

Malt(%) SV50(mPas) PV50(mPas) BR50(mPas/min)

0 1193 129 24 35 1015 180 1053 185 19 4

10 950 137 979 132 20 315 842 62 873 68 16 120 727 46 745 33 14 240 491 64 525 67 7 160 354 18 363 6 4 180 232 18 246 22 2 1

100 176 17 199 10 0 1

Full explanations of the abbreviations of the rheological parameters areoutlined in Fig. 2b.

8/14/2019 RVA.pdf

7/11

VOL. 111, NO. 2, 2005 171

glucan hydrolysing enzymes, caused increased viscosity,presumably due to the combination of molecular asym-metry and high molecular weight of -glucan. Whilst itwas shown that viscosity breakdown at 50C (BR50)could be attributed in part to glucanolytic enzymes12, itcan also be assumed that proteolytic and arabanolytic en-zymes play important roles in this degradation process.However, it had been previously shown14 in laboratorymashing experiments that little of the proteolytic break-down (that resulted in solubilised nitrogen) could be at-tributed to the endogenous malt enzymes acting on the un-malted barley substrate14.

With regard to starch gelatinisation and amylolyticbreakdown (Fig. 4), as the % malt was increased, thetrends observed (Table III) were a significant (P < 0.001)decrease in the rheological parameters recorded immedi-ately prior to primary gelatinisation and the parametersrecorded after gelatinisation such as: PVG, time at PVG,total area under the peak curve (PGA), area under thepeak curve with subtraction (PGAsubt), the rate of viscos-ity breakdown from PVG to the breakdown point (VB)and the rate of viscosity breakdown from PVG to theVE62. The primary gelatinisation temperature (GT) was

found to be significantly dependent on the level of barleyadjunct (P < 0.05). It tended to rise as the percentage ofmalt in the grist was increased (mean value of 58.8Cover the malt range of 020%; 59.7C at 100% malt). Thetime at gelatinisation (TG) increased, whilst the time toPVG reduced, as the percentage of malt was increased.The PVG decreased as the level of malt was increased(9930 44 mPas at 0% malt; 628 25 mPas at 100%malt) (Tables III, IV). When best-fit curves were appliedto the data versus the % malted barley, clear exponentialcorrelations could be made regarding the % malt from 5%to 100%, with regard to PVG (y = 18994x0.7342, R2 =

0.9988), PGA (y = 83438x0.6475, R2= 0.9928), PGAsubt(y = 88052x0.8866, R2 = 0.9967) and the VBR (y =1657.8x0.7901, R2 = 0.9783). The results clearly conferwith those previously shown in the Bohlin mash rheologi-cal studies11,12. In the studies13, it was clearly shown thatthe level of amylolytic breakdown following starch gelati-nisation determined the PVG. The VBR, was not only de-pendent on the level of amylase but also on the availabil-ity of under-hydrolysed substrate. A higher PVG (higherlevel of available substrate) resulted in a higher VBR.Therefore, both PVG and the VBR can be accurately rep-

Fig. 4.Rheological profiles of grist compositions representing various ratios of malt :barley adjunctover the course of the gelatinisation/liquefaction mashing step. (Top line = 5% malt; bottom line =100% malt.)

Table III.Rheological data of mashes containing increasing levels of unmalted barley adjunct over the course ofgelatinisation/liquefaction.

Malt

(%)

GT

(C)

TG

(min)

VG

(mPas)

PVG

(mPas)

Time at PVG

(min)

0 58.9 0.1 39.08 0.12 530 28 9930 44 43.01 0.035 58.9 0.3 39.09 0.29 488 9 5579 293 43.19 0.05

10 58.6 0.7 38.78 0.68 388 14 3556 132 42.89 0.1315 59.2 0.2 39.32 0.17 400 27 2699 134 42.84 0.1720 58.6 0.9 38.72 0.84 313 21 2106 52 42.71 0.0540 59.4 0.2 39.56 0.14 308 19 1299 50 42.55 0.0760 59.6 0.0 39.78 0.09 285 28 950 16 42.52 0.1480 59.6 0.1 39.72 0.08 229 7 748 14 42.35 0.13

100 59.7 0.1 39.94 0.06 211 12 628 25 42.21 0.13

Full explanations of the abbreviations of the rheological parameters are outlined in Fig. 2c.

8/14/2019 RVA.pdf

8/11


resented by the PGA and the PGAsubt. PGAsubt pertainsto the viscosity increases due to starch gelatinisation andliquefaction processes, without taking into considerationthe background under-lying viscosities associated with thenon-starch chemical composition of the sample. It hadpreviously been shown that ungelatinised starch alone wasa minor component of the viscosity immediately recordedprior to gelatinisation13. That inherent viscosity couldtherefore, be largely attributed to the remaining barleycomponents of -glucans, arabinoxylans, proteins etc,whilst the higher viscosities after gelatinisation could be

mainly attributed to low levels of amylolytic enzymes.With regard to the temperature stands at 63C and

72C (Fig. 5), as the % malt was increased, the trendsobserved (Tables IV, V) were a decrease in SV62, VE62,BR62, and VE72. These rheological data points werefound to be significantly dependent on the level of un-malted barley (P < 0.001). When best-fit curves were ap-plied to the data versus the % malted barley, clear correla-tions could be made regarding the % malt from 5% to100% with regard to viscosity breakdown rate from PVGto VE62 (y = 297.34x0.8187, R2= 0.9975) and the VE62 (y

= 2111.3x0.4813, R2 = 0.9901). The result clearly shows,the methods capability of detecting the hydrolysing abili-ties of the combined effects of - and -amylase in reduc-ing the molecular sizes of gelatinised starch and the resul-tant breakdown of the amylose, amylopectin structuresresulting in high, medium and low molecular weight dex-

Fig. 5.Rheological profiles of grist compositions representing various ratios of malt :barley adjunctfollowing gelatinisation, at the mash stands of 62C 40 min, 72C 20 min and 78C 5 min.R = Secondary Gelatinisation Points.

Table IV.Rheological data of mashes containing increasing levels of unmalted barley adjunct over the course ofliquefaction.

Malt

(%) PGA PGAsubtr

VBR

(mPas/min)

VBR62*

(mPas/min)

0 165306 8084 83578 5508 134.28 6.81 5 29091 276 19494 575 421.88 82.00 73.70 4.23

10 19222 2230 11877 1047 257.45 35.26 46.30 1.5315 14085 1164 7924 496 238.19 63.80 33.94 1.7820 11985 606 6705 267 153.30 17.40 26.67 0.9840 7839 676 3508 192 93.10 5.19 15.00 0.5060 6343 776 2360 128 61.30 12.50 10.20 0.3580 4324 63 1725 22 60.70 1.40 8.11 0.29

100 4404 495 1424 42 36.70 10.40 6.61 0.37

* = VBR62 refers to the viscosity breakdown rate [(VPG VE62)/Time].

Full explanations of the abbreviations of the rheological parameters are outlined in Figs. 2c and 2d.

Table V.Rheological data of mashes containing increasing levels of un-malted barley adjunct over the course of saccharification and mash-off.

Malt(%)

Drop-off rate*(mPas/min)

BR72(mPas/min)

VE78(mPas)

0 7239 1044 2691 10025 5097 267 1.14 0.66 482 42

10 3257 106 1.78 0.39 299 4315 2395 143 1.80 0.75 304 1020 1898 72 1.74 0.45 208 2240 1098 49 1.84 0.42 201 460 739 7 1.26 0.21 211 1980 597 36 1.18 0.36 152 25

100 476 30 0.98 0.20 153 8

*The drop-off rate refers to [(PGA VE78)/ Time].

Full explanations of the abbreviations of the rheological parameters areoutlined in Fig. 2d.

8/14/2019 RVA.pdf

9/11

VOL. 111, NO. 2, 2005 173

trins. However, no significant variability in results werefound with regard to the BR72 due to the level of barleyadjunct. This would suggest the inability of the method toshow the sugar-hydrolysing effects of the -amylase, inconverting high molecular weight dextrins to mediumand low molecular weight sugars. The VE78 was foundto weakly correlate with level of barley adjunct (y =705.62x0.3323, R2 = 0.8960). The mash viscosity at thispoint is reflective of both the quality and degree of modi-

fication of the grist material, the effectiveness of themashing programme and the unsolubilised grain compo-nents/particles and the wort soluble proteins (high andlow molecular weight), -glucans and sugars. From previ-ous studies14 it has been shown that as the ratio of malt:barley adjunct is increased, the resultant worts are higherin total levels of extract. This extract is composed oflower levels of high molecular weight -glucan, increasedlevels of fermentable sugars, glucose and maltotriose andunfermentable middle molecular weight dextrins (DP4DP7) together with higher levels of total soluble nitrogen(high and low molecular weight nitrogen fractions). Inaddition, it is composed of lower levels of high molecularweight dextrins (DP 8). At the lower levels of grist

modification, the higher levels of high molecular weightdextrins (DP 8) and high molecular weight -glucans ofthe wort together with undegraded arabinoxylans wouldcontribute greatly to the mash viscosity 25, whilst the resid-ual undegraded un-solubilised viscosity creating macro-molecular components of the grain particles would alsocontribute greatly to the mash viscosity.

In addition, when one looks more closely at Fig. 5, oc-casional increases in viscosities are noted. This was alsonoted in other rheological studies12,13,15. These increasesare more noticeable at the higher levels of unmalted bar-ley adjunct. It has already been hypothesised that thesepeaks represent secondary gelatinisation points12,13. Thegelatinisation temperature of starch is influenced not only

by the type of starch but also by the size and structure ofits starch granules23. It is well reported in the case of bi-modal barley starches, that the small starch granules havehigher temperatures of gelatinisation19. Barley starchgranules are reported to be of two different granularsizes23. The large and smaller granules are referred to asA- and B-type granules respectively. Reports show thatthere is a wide variation in the granule size distribution ofbarley starch. In general small granules (B-type) are takento be those less than 6 m in diameter (more often 24m in diameter). These constitute 8090% of the totalnumber of starch granules but generally only 1015% ofthe total starch weight. Large granules (A-type) range insize from 10 to 30 m but generally lie in the 1520 m

range. They constitute a small proportion (1020%) of thetotal number of starch granules but a high proportion (8590%) of the total weight of starch 23. In most cases, rawunmalted barley has higher levels of small starch gran-ules, than malted barley, since during the malting processthe small granules are preferentially degraded 2. The re-ported negative impacts of small starch granules are thatdue to higher temperatures of gelatinisation they are lessdigestible during mashing. It is difficult for amylases toattack these granules during mashing as they are sur-rounded by more protein matrix in the endosperm cells4.

In addition, they can impede wort filtration by cross-link-ing with other polymers1. It had been previously shown inthe Bohlin mash rheological studies13that, the increases inviscosity, due to the secondary gelatinisation processes,were found to closely correlate with the level of addedamylase. It was reported, that if mash amylase levels werehigh enough, then these secondary starch viscosity peakswould not be observed under the Bohlin mash rheologicalmethod13.

In agreement with the previously developed Bohlinmash rheological method1113, the developed RVA rheo-logical method gives an in-sight into the various biochemi-cal and physical processes that are happening during mashprocessing of these malt:barley adjunct combinations.Indications of the levels of endogenous enzymes withinthe systems and their abilities to breakdown the macro-molecular viscosity causing substances are very evident.This method provides a very good indication of the in-trinsic mash-hydrolytic processes of proteolysis, -glucanbreakdown and starch conversion. Rather than just gain-ing information regarding the chemical and physical prop-erties of the grains or their wort soluble end products, themethod more closely follows the grain processabilities

during mash conversion processes. Because the time/tem-perature conditions closely represent industrial type pro-cesses, in comparison to other RVA studies where thegrains endogenous enzyme systems were not optimised(such as Glennie Holmes610), it can give the brewer closerindications as to how the addition of different levels ofbarley adjunct could perform in an industrial brewing pro-cess.

In addition the results from these experiments havedemonstrated the potential of the RVA mash rheologicalmethods for many other applications. These may includethe assessment of the application of commercial enzymepreparations when brewing with high adjunct ratios, theassessment of different barley, malt genotypes for brewing

purposes. Likewise, with further development, the RVAmash rheological method could provide a very useful toolfor indirectly monitoring the biochemical and physicaltransformations that are taking place during the maltingprocess. Green malt samples can be taken during the vari-ous stages of the malting process and subjected to thedeveloped rheological method. Enzyme development andmodification processes during barley germination, to-gether with enzyme preservation/inactivation during kiln-ing regimes can thus be followed. The RVA mash rheo-logical method could thus provide the maltster with anincreased physical knowledge of their processes and thusact as a tool to identify potential problems and enablecritical decisions to be made.

This study has also provided us with the possibility ofmaking general comparisons between the RVA and thepreviously mentioned Bohlin method as mash rheologicaldetermination instruments. With reference to a previouspublication by the current authors1113 where the Bohlinmash rheological method was also successfully utilizedfor looking at different ratios of barley adjunct, closecomparisons could be made between the results of thosemethods and the results of the current study. Therefore,both methods can be deemed suitable for determiningmash rheological profiles. The main advantages of the de-

8/14/2019 RVA.pdf

10/11


veloped RVA mash rheological method, over the previ-ously mentioned Bohlin mash rheological method, are thatin comparison to the Bohlin method (where results werequoted as arbitrary units), the RVA viscometer is fullydesigned and calibrated to give readouts in standard vis-cosity units (mPa.s). The RVA was also judged by the cur-rent authors to be less sensitive to localised disturbancesin the laboratory environment such as bench vibrations,air draughts etc. It was also judged to be more user-

friendly, than the developed Bohlin method, in that one-way plastic paddles and disposable aluminium canisters,together with an easy to operate dedicated software pro-gramme are employed. Therefore, samples can be pro-cessed more quickly, with less risk of sample cross con-tamination. Perhaps the most notable advantage is that,the RVA is considerably cheaper to purchase. Therefore,transfer of the developed methods to the malting/brew-ing/distilling industries, would not be hampered by ex-cessive costs and initial capital investment.

CONCLUSIONS

This study has shown that the RVA is an instrument ca-pable of carrying out a mash rheological analysis. An RVArheological profile can provide the brewer with a detailedpicture of the processes that are taking place during mash-ing. The RVA has the ability of not only detecting the ma-jor viscosity changes which occur during starch gelatini-sation/liquefaction processes, but also the minor viscositychanges which were found to occur during the mash pro-teolytic and saccharification steps. Clear correlations werefound between the rheological data over the course of the50C, 62C, 72C, 78C mash stands and the controlledamount of barley adjunct. Increasing the level of raw bar-ley adjunct resulted in an increase in viscosities over thecourse of the 50C, 62C, 72C and 78C mash stands.

This was indicative of the viscosity causing un-modifiedstructural components of barley adjunct together with thefully-modified structural components of the malted barley,interacting with the endogenous viscosity hydrolysing maltenzymes. RVA mash rheological profiling can thus offeran insight into how raw materials interact. Increased pre-knowledge of such processes may provide the maltster/brewer/distiller with more functional information regard-ing raw materials and brew-house processing conditions.

ACKNOWLEDGEMENTS

The authors would like to acknowledge that this project waspartly financed by Enterprise Ireland and the Food Industry Re-

search Measure (FIRM) under the National Development Plan,20002006 with co-financing by the European Commissionunder the European Regional Development Fund. In addition,we would like to gratefully acknowledge the part funding of theRapid Visco-Analyser by Irish Distillers Ltd, Pernod RicardGroup, Midleton, Co. Cork, Ireland.

REFERENCES

1. Barrett, J., Clapperton, J.F., Divers, D.M. and Rennie, H., Fac-tors affecting wort separation. Journal of the Institute of Brew-ing,1973, 79, 407413.

2. Bathgate, G.N. and Palmer, G.H., The in vivo and in vitro deg-radation of barley and malt starch granules.Journal of the Insti-tute of Brewing,1973, 79, 402406.

3. Broadhead, A.L., Brosnan, J.M. and Bringhurst, T.A., The roleof the Rapid Visco Analyser (RVA) in minimizing distillery pro-cessing problems. In: Distilled Spirits: Tradition and Innovation.J.H. Bryce and G.G. Stewart (Eds.). Publisher: Iowa State,2004, Chapt. 13, pp. 8995.

4. Ellis, R.P., The use of high amylase barley for the production ofwhiskey malt. Journal of the Institute of Brewing, 1976, 82,

280281.5. European Brewery Convention. Analytica EBC,5th ed. VerlagHans Carl: Nrnberg, Germany, 1998.

6. Glennie Holmes, M.R., Studies on barley and malt with therapid viscoanalyser: (I) The effects of the variation in physicaland chemical parameters.Journal of Institute of Brewing,1995,

101, 1518.7. Glennie Holmes, M.R., Studies on barley and malt with the

rapid viscoanalyser: (II) The effects of modification on visco-grams.Journal of Institute of Brewing,1995, 101, 1928.

8. Glennie Holmes, M.R., Studies on barley and malt with the rapidviscoanalyser: (III) The prediction of malting potential from vis-cograms.Journal of the Institute of Brewing,1995, 101, 2932.

9. Glennie Holmes, M.R., Studies on barley and malt with therapid viscoanalyser: (IV) Amyloclasis, amylolysis and cyto-clasis of malt and malting quality. Journal of the Institute of

Brewing,1995, 101, 3338.10. Glennie Holmes, M.R., Uses for the rapid viscoanalyser in abrewery. Tech. Q. Master Brew. Assoc. Am.,1995, 32, 7275.

11. Goode, D.L., Rapp, L., Schober, T.J., Ulmer, H.M. and Arendt,E.K., Rheological studies simulating the brewery mashing pro-cess. Proceedings of the World Brewing Congress, San Diego,California, USA, Oral Presentation 97.

12. Goode, D.L., Rapp, L., Schober, T.J., Ulmer, H.M. and Arendt,E.K., Development of a new rheological laboratory method formash systems its application in the characterization of grainmodification levels.Journal of the American Society of BrewingChemists,2005, 63(2), 7686.

13. Goode, D.L., Ulmer, H.M, and Arendt, E.K., Model studies tounderstand the effects of amylase addition and pH adjustmenton the rheological behaviour of simulated brewery mashes.

Journal of the Institute of Brewing,2005, 111(2), 153164.

14.Goode, D.L., Wijngaard, H.H., and Arendt, E.K., Mashing withunmalted barley impact of malted barley and commercial en-zyme (Bacillus subtilis) additions. Tech. Q. Master Brew. Assoc.

Am.,2005, 42, 184198.15. Hermann, J. and Sommer, K., Development of a device to deter-

mine the rheology of mash. Tech. Q. Master Brew. Assoc. Am.,2001, 38, 5558.

16. Hoog, D., Senge, B. and Annemuller, G., Rheologische Kon-trolle von Labormaischen.Brauwelt,1997, 37, 16061610.

17. ICC Standards Standard methods of the International Associa-tion for Cereal Chemistry (ICC). Hans Kock Buch- und Offset-druck GmbH, Germany.

18. Kunze, W., Technology Brewing and Malting, 2nd edition,VLB: Berlin, Germany, 1999.

19. Lindeboom, N., Chang, P.R. and Tyler, R.T., Analytical, bio-chemical and physicochemical aspects of starch granule size,

with emphasis on small granule starches: a review.Starch/Strke,2004, 56, 8999.

20. Lloyd, W.J.W., Evaluation of malt in a malting company. Jour-nal of the Institute of Brewing,1978, 84, 7778.

21. Lloyd, W.J.W., The relevance of amylogram characteristics inmalt evaluation. Tech. Q. Master Brew. Assoc. Am., 1979, 16,6067.

22. Lorenz, K. and Kulp, K., Sprouting of cereal grains Effects onstarch characteristics. Starch,1981, 33, 183187.

23. MacGregor A.W. and Fincher, G.B., Carbohydrates of the bar-ley grain. In: Barley: Chemistry and Technology. A.W. Mac-Gregor and Bhatty, R.S., Eds. American Association of CerealChemists, Inc: St. Paul, Minnesota, USA, 1993, pp. 73130.

8/14/2019 RVA.pdf

11/11

VOL. 111, NO. 2, 2005 175

24. Narziss, L., Die Technologie der Wurzebereitung, 7th edition,Ferdinand Enke Verlag: Stuttgart, Germany, 1992.

25. Sadosky, P., Schwarz, P.B. and Horsley, R.D., Effect of arabi-noxylans, -glucans, and dextrins on the viscosity and mem-brane filterability of a beer model solution. Journal of the

American Society of Brewing Chemists,2002, 60, 153162.26. Senge, B., Schwarzlos, B., Blochwitz, R. and Annemuller, G.,

Rheological examination of mashing in the brewery process.Applied Rheology,1996, 6, 1118.

27. Woodward, J.D. and Oliver, W.B., Varietal features affectingmashing performance. Proceedings of the European BreweryConvention Congress, Zurich, 1989, pp. 299306.

28. Yoshida, T. and Yamada, K., Assessment of malt quality withthe Brabender Viscograph. Journal of the Institute of Brewing,1970, 76, 455464.

(Manuscript accepted for publication April 2005)

RVA.pdf

Documents

Transcript of RVA.pdf