薄层干燥Thin-layer drying of spent grains in superheated steam

Thin-layer drying of spent grains in superheated steamZhongwei Tang a ,Stefan Cenkowskia,*,Marta IzydorczykbaDepartment of Biosystems Engineering,University of Manitoba,Winnipeg,MB,Canada R3T 5V6bGrain Research Laboratory,Canadian Grain Commission,303Main Street,Winnipeg,MB,Canada R3C 3G8Received 24April 2002;revised 21November 2003;accepted 29April 2004AbstractAn empirical equation with regression-determined coefficients was developed to describe thin-layer drying of brewers Õspent grain (BSG)and distillers Õspent grain (DSG)in superheated steam (SS).A small moisture gain on the sample surface due to steam condensation at the beginning of the drying caused the initial moisture ratio of the sample to increase to a value between 1.00and 1.20for BSG drying or between 1.00and 1.30for DSG drying.The moisture gain increased linearly with decreasing the temper-ature and/or velocity of steam.Unlike in hot-air drying,not only steam temperature but also steam velocity influenced the drying rate of BSG and DSG in SS.At 145°C,an increase in steam velocity from 0.3to 1.1m/s cut the drying time by half for both spent grains.Increasing the SS drying temperature from 110to 180°C decreased the starch content in samples dried to the equilibrium moisture at the SS velocity of 0.66m/s by 14.5%and 11.5%for BSG and DSG,respectively.Drying to the equilibrium in 145°C at a SS velocity of 0.66m/s caused the starch content in the samples to decrease by 22%for BSG and 23%for DSG compared with that in the non-dried material.The SS drying parameters had no effect on b -glucan,pentosan,and protein contents in the dried samples.Ó2004Elsevier Ltd.All rights reserved.Keywords:Brewers Õgrain;Distillers Õgrain;Superheated steam;Drying;Nutrient composition1.IntroductionSpent grains are the by-products from the production of alcoholic beverages and ethanol fuels.Brewers Õspent grain (BSG)is the residue of beer making in breweries,which use malted barley as the major raw material (Johnson &Peterson,1974).Distillers Õspent grain (DSG)is the product left in distilleries after alcohol is re-moved by distillation from the fermented grains such as corn,wheat,barley,rice,and rye (Wampler &Gould,1984;Woods,Husain,&Mujumdar,1994).Protein,fat,and fiber are highly concentrated in spent grains be-cause most of the starch in the raw materials has been removed and converted to alcohol and carbon dioxide during fermentation (Kissell &Prentice,1979;Wampler &Gould,1984).Therefore,spent grains are excellent sources of protein and energy.They are mainly used as feed for animals such as cattle and poultry,and they can also be used as flour supplement to produce human food products such as baked foods,extruded snacks,and baby foods (Rasco,Rubenthaler,Borhan,&Dong,1990;Wu,Sexson,&Lagoda,1984).To prolong the storage time of spent grains and to re-duce their mass (consequently to lower the transporta-tion cost),spent grains need to be dried to about 10%moisture content (wet basis,wb)(Woods et al.,1994).The traditional drying operation (e.g.,heated-air drying in rotary-drum dryers)is energy-intensive.To save0260-8774/$-see front matter Ó2004Elsevier Ltd.All rights reserved.doi:10.1016/j.jfoodeng.2004.04.040*Corresponding author.Tel.:+12044746033;fax:+12044747512.E-mail address:stefan_cenkowski@umanitoba.ca (S.Cenkowski)./locate/jfoodengJournal of Food Engineering 67(2005)457–465energy,superheated steam(SS)could be used for drying spent grains.Woods et al.(1994)proposed afluid-bed SS drying system for the drying of DSG.The circulation of SS in the closed-loop drying system can reduce the energy wastage that occurs with hot-air drying.Also,the ex-haust steam produced from the evaporation of moisture from the wet product can be used in other operations in the distilleries,such as cooking raw materials,stripping and rectifying distillation of ethanol,and concentrating residual stillage.In addition to the reduced energy consumption,drying in SS has numerous other merits compared with traditional hot-air drying.These are: a reduction in the environmental impact,an improve-ment in drying efficiency,the elimination offire or explosion risk,and a recovery of valuable volatile or-ganic compounds(Dibella,1996;Erdesz&Kudra, 1990;Jensen,1992;Meunier&Munz,1986;Wimmer-stedt,1995).However,the application of this drying technique needs more complex drying equipment com-pared with hot-air drying,and high-temperature of the product in SS drying creates a problem for tempera-ture-sensitive products(Kumar&Mujumdar,1990;Shi-bata,1991).Leading manufactures of drying equipment, looking for the most effective technique,introduced pressurized-steamfluid-bed dryers for dryingfibrous or granular materials(Bonazzi et al.,1996).Also,a number of products such as green teas,sugar-beet pulp, potatoes,noodles,lumber,paper,sludge,and activated carbon pellets have been studied and found to be suita-ble for processing and drying with SS(Douglas,1994; Markowski,Cenkowski,Hatcher,Dexter,&Edwards, 2003;Tang&Cenkowski,2000;Urbaniec&Malczews-ki,1997;Wimmerstedt&Hager,1996).To our knowledge,no systematic studies on drying spent grains using SS have been reported in the litera-ture except for the experimental drying of wheat-de-rived stillage in Europe(Woods et al.,1994).Drying kinetics of a layer of material in a drying-medium stream can be studied using a thin-layer drying ap-proach(Jayas,Cenkowski,Pabis,&Muir,1991),which can provide the base for modelling practical deep-bed drying.An equation describing thin-layer drying can be incorporated into a group of equations to describe the drying process of a deep bed of material.Thin-layer drying is a drying process in which the drying condi-tions or potential of the drying medium remains un-changed when the drying medium passes through the material to be dried.In contrast,in deep-bed drying the drying conditions change in the direction of the flow of drying medium.The objectives of this study were:(a)to develop equations for describing the thin-layer drying of BSG and DSG in SS,(b)to analyse the thin-layer drying characteristics of spent grains in SS,and(c)to quantify the change in nutrient composi-tion of the dried samples.2.Experiments for thin-layer drying of spent grains in superheated steam2.1.MaterialsThe materials used in the experiments were brewersÕbarley spent grain and distillersÕwheat spent grain, which were obtained from a local brewery(Fort Garry Company Ltd.,Winnipeg,MB)and a distillery(Mo-hawk Canada Ltd.,Minnedosa,MB).The materials were stored in a deep freezer atÀ15°C and thawed at room temperature before the drying experiments.The initial moisture contents of the two tested products were 4.22±0.15kg/kg dry basis(db)for BSG and2.17±0.15 kg/kg db for DSG.The moisture contents were deter-mined by the vacuum-oven drying method(AACC, 1995).Each sample prepared for the thin-layer drying experiments weighed approximately8.8g for BSG and 6.1g for DSG.2.2.EquipmentThe equipment used in the experiments was the SS drying system developed in the Department of Biosys-tems Engineering at the University of Manitoba.The system consisted of a steam generator,a pressure reg-ulator,a steam-flow valve,a steam conveying pipeline, a drying chamber,auxiliary heaters,a hot-air supply system,and a data acquisition and control system. Saturated steam at580kPa and158°C was produced by the steam generator.Its pressure was reduced to 130kPa when the steam passed through the pressure regulator,and thus SS was generated.The pressure of the steam passing through the drying chamber dropped down to100kPa due to the frictional loss in the pipeline.The steam-flow rate or velocity was controlled by the steam-flow valve.The steam was adjusted to the preselected temperature by the auxil-iary heaters in the pipeline before passing through the drying chamber.The drying system was fully described elsewhere(Tang&Cenkowski,2000;Tang, Cenkowski,&Muir,2000).To ensure that the steam passes through the sample to be dried,a metal plate with a central round opening(69mm in diameter) was placed in the middle section of the drying cham-ber(Fig.1).During drying,the circular mesh tray(68 mm in diameter,with a10mmflange)with the sam-ple was placed in the central opening and hung by a thin wire from an electronic balance located on the top of the drying chamber.Theflange of the tray was approximately4mm above the plate.Only a small fraction of steam was allowed to escape through the gap between the sample tray and the plate.This fraction was quantified experimentally,and the deter-mination of the steam velocity through the sample was adjusted for that.458Z.Tang et al./Journal of Food Engineering67(2005)457–4652.3.Drying conditionsDrying experiments were conducted under atmos-pheric pressure.The steam temperature at the inlet to the drying chamber was controlled at seven levels:110, 115,120,130,145,160,and180°C with the accuracy of±3°C.The velocity of steam passing through the sample to be dried was set atfive values:0.25,0.47, 0.66,0.86,and1.08m/s with the accuracy of±0.06m/ s for BSG drying,and0.28,0.49,0.70,0.92,and1.15 m/s with the accuracy of±0.06m/s for DSG drying. The steam velocity was adjusted by the steam-flow valve;it was calculated based on the amount of con-densed water collected from the condenser in a certain time,the fraction of steam escaped through the gap be-tween the sample tray and the plate,and the steam tem-perature inside the drying chamber.To determine the fraction of the escaped steam,the following experiments were conducted.Hot air(70°C)instead of steam was used as the drying medium for convenience.The tray with the same amount of sample as in normal drying experiments was changed alternatively several times dur-ing the test between two positions:A and B.Position A was the normal drying position in which the tray was hung in the drying chamber from the balance and the flange of the tray was about4mm above the plate.At position B,the tray was seated on the plate with its flange contacting the plate,and all the hot air was forced to pass through the sample.At each position,the air velocities were measured with a thermal anemometer (Model HHF50,OMEGA Engineering,Inc.,Stamford, CT)at two or three selected points approximately20 mm above the sample.Four runs of tests were con-ducted at different air-velocity levels covering the typical experimental range(0.25–1.15m/s)of steam velocity for normal drying experiments.The average velocity of the air passing through the sample at position A was lower by14.8%for BSG drying and13.9%for DSG drying compared with that at position B.This means that 14.8%and13.9%of the drying medium passing through the chamber escaped from the gap between the sample tray and the plate during the normal experiments for BSG and DSG drying,respectively.The shrinkage of the sample during drying had no substantial effect on the amount of the drying medium passing through the sample or the gap between the tray and the plate because of the small size of samples used(8.8g for BSG and 6.1g for DSG).2.4.Experimental procedure for drying testsDuring drying,the sample was placed in a thin layer on the mesh tray which was hung in the drying chamber by a thin wire attached to the electronic balance(Fig.1). The mass change was recorded every2or3s by a com-puter connected to the balance.The drying process was ended when the mass of the sample remained constant for2–5min depending on the total drying time.Under each set of drying conditions,tests were conducted in triplicates.Theflow of steam created a‘‘lifting force’’which af-fected the mass-change readings.The‘‘lifting force’’changed non-linearly with moisture loss during drying due to the shrinkage of the sample.To compensate for this apparent loss in mass,a calibration test was con-ducted immediately after each drying test.In the calibra-tion test,the steam conditions were kept the same as in the previous drying test;however,the drying medium was manually controlled to bypass the drying chamber for10–15s every0.5–2min.At a selected moisture point,the difference between the readings with and with-out steam passing through the chamber in the calibra-tion test was the‘‘lifting force’’on the sample at that moisture point.The‘‘lifting force’’was incorporated into the calculation of true mass loss of the sample in the corresponding drying test.Fig.1.Superheated steam thin-layer drying chamber(dimensions are in mm).Z.Tang et al./Journal of Food Engineering67(2005)457–4654592.5.Determination of nutrient compositionThe benefits of the utilization of BSG and DSG de-pend on the nutrient composition of these materials. To quantify the effects of drying conditions on the nutri-ent composition of spent grains,the samples dried at se-lected steam temperatures and for different drying times were analyzed for composition and compared with non-processed(undried)material.Each sample of approxi-mately10g was tested in this analysis.Four major nutrient components(starch,b-glucan,pentosan,and protein)in the samples were chosen for measurements. b-Glucan and pentosan were determined because both these non-starch polysaccharides are constituents of die-taryfiber.The presence of dietaryfiber makes spent grains attractive for human consumption(but not neces-sarily for animal feeds).The mixed-linkage b-glucan assay kit(Megazyme International Ireland,Ltd.)was used for the b-glucan measurement(McCleary&Codd, 1991).The phloroglucinol method of Douglas(1981) was used for measuring colorimetrically the content of pentosan.Starch content was determined enzymatically using the Megazyme kit for total starch assay (Megazyme International Ireland,Ltd.)(McCleary, Solah,&Gibson,1994).Protein content was determined by combustion nitrogen analysis(CNA)using a LECO Model FP-428CNA analyzer(Leco Corp.,St.Joseph, MI)calibrated against ethylenediaminetetraacetic acid.3.Empirical equation for spent grains dried in superheated steamIn most models developed for drying large size or compact products in SS,an overpressure built-up inside the products is considered as one of the important driv-ing forces during the falling-rate drying period(Hager, Hermansson,&Wimmerstedt,1997;Perre,Moser,& Martin,1993).The involvement of the overpressure makes the modelling more complex.However,there is no significant overpressure inside spent grains during steam drying because spent grains are in a chopped or ground state(Bonazzi et al.,1996).Therefore,the gener-al modelling technique considering the overpressure as the third driving force is not suitable for modelling the thin-layer drying of spent grains in SS.Based on observations in previous studies(Tang& Cenkowski,2000;Tang et al.,2000),when drying of such biological materials as sugar-beet pulp and sliced potatoes,the drying curves in the falling-rate period are of similar shapes for SS drying and hot-air drying, therefore,a similar form of empirical equation for air drying could be used for describing the SS drying kinetics.One of the most often used empirical equations for describing air drying of a thin layer of biological mate-rials is PageÕs equation(Page,1949;cited by Jayas et al.,1991):MR¼expðÀKt NÞð1Þwhere MR=moisture ratio;K,N=experimental param-eters;t=drying time(min).The moisture ratio is defined as:MR¼MÀM eM0ÀM eð2Þwhere M=moisture content(kg/kg db);M e=equilib-rium moisture content(kg/kg db);M0=initial moisture content(kg/kg db).In Eq.(1)the initial moisture ratio at time0becomes 1.At the beginning of SS drying,however,a small amount of moisture is gained on the sample surface from the steam condensation while the sample is brought up from the room temperature to100°C.The steam con-densation takes place in such a short time(several sec-onds)that it is not feasible to describe mathematically that short initial period of drying(Markowski et al., 2003).In consequence,the initial moisture ratio for SS drying becomes greater than1(e.g.,see insert in Fig.3).Therefore,a third experimental parameter A was introduced into Eq.(1)to accommodate the surface con-densation problem in SS thin-layer drying:MR¼A expðÀKt NÞð3ÞIn Eq.(3),the parameters A,K,and N are dependent on the steam temperature and/or steam velocity.The equi-librium moisture content M e in Eq.(2)is dependent on the steam temperature T,which has been determined in a previous study(Tang&Cenkowski,2001):M e¼0:6538exp½À1:1605ðTÀ100Þ0:3269ðfor BSGÞð4ÞM e¼0:1389exp½À0:3024ðTÀ100Þ0:5609ðfor DSGÞð5ÞUsing non-linear regression and considering moisture ratio MR and drying time t as the regression variables, the parameters A,K,and N in the empirical equation (Eq.(3))were determined for each set of drying condi-tions.The regression was accomplished by the NLIN procedure in SAS system(SAS,1985).From the regression results,it was noted that param-eter A decreased and parameter K increased approxi-mately linearly with the increase in steam temperature T and velocity V.But parameter N increased approxi-mately linearly only with the steam temperature increase. Therefore,these relationships were represented as:A¼ða1Tþa2Þða3Vþa4Þð6ÞK¼ðk1Tþk2Þðk3Vþk4Þð7Þ460Z.Tang et al./Journal of Food Engineering67(2005)457–465N ¼n 1T þn 2ð8Þwhere a 1,a 2,a 3,a 4,k 1,k 2,k 3,k 4,n 1,and n 2are coeffi-cients.The coefficients in Eqs.(6)–(8)were obtained by further regression in which parameters A (or K ,or N ),T ,and V were considered as the regression variables (Table 1).The small mean residual squares of MR shown in Table 1indicate that the regression equations have an acceptable accuracy for fitting the experimental data.Drying curves predicted by the equations under selected drying conditions and the corresponding measured data points were plotted in Figs.2and 3.The figures also show that the empirical equation with the obtained regression coefficients fits the experimental data well and is suitable in modelling deep-bed drying (Tang,Cenkowski,&Muir,2004).4.Drying dynamics of a thin layer of spent grains in superheated steamBased on the empirical equation developed above,the moisture ratios,moisture contents,and drying rates of thin layers of spent grains dried in SS can be predicted at drying conditions in the range defined in this study.Drying curves and drying-rate curves for selected drying conditions were plotted to present the drying dynamics of thin layers of spent grains in SS (Figs.4–7).The drying curves show the changes of moisture ratio with drying time,and the drying-rate curves represent the changes of drying rate with moisture content.The dry-ing rate is defined here as the change of moisture content in unit time,i.e.,the differentiation of moisture content d M /d t :d Md t¼ÀAKN ðM 0ÀM e Þt ðN À1Þexp ðÀKt N Þð9ÞBecause of steam condensation,the samples gained a small amount of moisture in the first several seconds of drying.The samples gained more moisture in low-temperature or low-velocity steam than in high-temper-ature or high-velocity steam.The moisture gain changed linearly with a change in steam temperature or velocity.At 0.7m/s,for example,the moisture gain caused an in-crease in the initial moisture ratios to 1.15,1.13,and 1.11for BSG samples (or 1.21, 1.13,and 1.05for DSG samples)for the steam temperatures of 110,145,Table 1Regression coefficients in Eqs.(6)–(8)ParameterBSG drying model DSG drying model Aa 1À0.00058À0.00135a 2 1.29250.8375a 3À0.0963À0.2778a 40.9991 1.9578Kk 10.002730.00388k 2À0.2609À0.3741k 3 2.0984 2.0399k 40.21740.2199Nn 10.002220.00557n 20.95990.5185Mean residual square of MR0.00160.0021Z.Tang et al./Journal of Food Engineering 67(2005)457–465461and180°C,respectively(Fig.4).At145°C,the mois-ture ratios at the beginning of drying reached 1.18, 1.13,and 1.08for BSG samples(or 1.20, 1.13,and 1.06for DSG samples)for the steam velocities of0.3, 0.7,and1.1m/s,respectively(Fig.5).A certain amount of sensible heat is needed to bring a sample from its room temperature to100°C.This heat is supplied by the steam.When the temperature of steam decreases, the sensible heat of the steam decreases as well,there-fore,increased steam condensation takes place to pro-vide the required heat for warming up the sample to the saturation point for steam(100°C at the atmos-pheric pressure).The effect of steam velocity on the steam condensation could be explained based on the heat-transfer analysis.Less heat is transferred from lower-velocity steam to the sample by convection be-cause of the lower heat-transfer coefficient between the steam and the sample,therefore,a higher deposition of condensate is observed before this process is reversed into drying.There was no constant-rate drying period noticeable for the thin-layer drying of spent grains in SS.The dry-ing rate decreased gradually during SS drying except for a short initial warm-up period,during which the drying462Z.Tang et al./Journal of Food Engineering67(2005)457–465rate increased rapidly(Figs.6and7).This agrees with drying in SS of such biological products as potatoes, sugar-beet pulp,and Asian noodles(Markowski et al., 2003;Tang&Cenkowski,2000;Tang et al.,2000).In thin-layer drying of spent grains in SS,the drying rate increased nearly linearly with an increase in steam temperature(Fig.6).This is similar to thin-layer drying of biological materials in hot air.However,unlike hot-air drying in which the velocity of drying medium has no effect on the drying dynamics in the falling-rate per-iod(Jayas et al.,1991;Salgado,Lebert,Garcia,&Bim-benet,1994),the steam velocity evidently affected the SS drying dynamics.Moisture content decreased faster at high velocity than at low velocity of steam(Fig.5).At 145°C,the drying times for reaching the equilibrium were21,13,and9min for BSG drying(or16,10,and 7min for DSG drying)at the velocities of0.3,0.7, and 1.1m/s,respectively.Increasing the velocity of steam from0.3to1.1m/s decreased the drying time by 57%for BSG drying(or56%for DSG drying).During the SS drying process except for the initial period,the drying rate increased nearly linearly with the increase of steam velocity(Fig.7).For example,at145°C and when the samples were dried to the moisture content of1kg/kg db,an increase of steam velocity from0.3 to0.7and1.1m/s caused an increase of the drying rate from0.26to0.44and0.601/min for BSG drying(or from0.32to0.53and0.711/min for DSG drying),respectively.Superheated steam drying has a different drying mechanism in the falling-rate drying period com-pared with hot-air drying.In hot-air drying,the drying rate is governed by the diffusion of moisture or water va-por or a mixture of both(Strumillo&Kudra,1986).The major limiting factor in air drying is the internal resis-tance to mass transfer,which has no relation to the ve-locity of the drying air.During SS drying,an overpressure built-up inside the material to be dried (even though very small)makes the internal resistance to mass transfer negligible(Hager,1998;Khan&Beas-ley,1988).The rate of evaporation or drying in SS is mainly controlled by the rate of heat transfer between the drying medium(superheated steam)and the material to be dried.The heat-transfer coefficient is closely corre-lated to the velocity of the SS.Therefore,the velocity of steam plays an important role in SS drying.5.Effects of drying temperature and time on nutrient compositionThe nutrient composition of undried spent grains (control)and the samples dried in SS under various con-ditions is presented in Table2.The undried BSG con-tained more starch but less b-glucans compared with the undried DSG.Both materials contained considera-ble amounts of pentosans and proteins.In general,theTable2Nutrient composition of undried and dried a spent grain samplesDrying temperature(°C)Dryingtime(min)bStarch(%,db)b-Glucans(%,db)c Pentosans(%,db)c Proteins(%,db)Ave.d Std.dev.Ave.d Std.dev.Ave.d Std.dev.Ave.e Std.dev.BSG11036 6.830.490.760.0319.45 1.0424.510.06 14511.5 5.840.030.760.0119.48 1.9322.900.26 1807.5 5.840.210.750.0222.64 1.8424.430.06 Undried7.490.020.780.0324.97 4.7824.510.29145(3)7.220.120.760.0320.64 4.2524.66–145(6) 6.270.290.770.0122.09 4.0823.30–14511.5 5.840.030.760.0119.48 1.9322.900.26DSG11049 2.080.01 1.620.0319.73 1.6527.21–14517 1.930.01 1.490.0120.860.6727.300.11 18010 1.840.00 1.440.0121.20 4.7928.15–Undried 2.500.03 1.500.0121.59 2.3726.50–145(4.5) 2.380.10 1.700.0717.930.5627.350.11145(9) 2.190.04 1.630.0320.68 1.6827.38–14517 1.930.01 1.490.0120.860.6727.30–a Dried in superheated steam at the steam velocity of0.66m/s and different temperatures for different times.b Times for drying to equilibrium except those in parentheses.c Samples washed with ethanol prior to treatment.d Average of two results.e Average of two results with std.dev.only.Z.Tang et al./Journal of Food Engineering67(2005)457–465463effect of drying on the amounts of nutrients in the sam-ples was rather small.Among the four components measured,starch was affected to the greatest extent. Both drying temperature and time had some effect on the starch content in the dried samples.All dried BSG and DSG had lower starch content than the undried (control)samples.Increasing the drying temperature from110to180°C decreased the starch in the samples dried to the equilibrium at the steam velocity of0.66m/s from6.83%to5.84±0.24%(decrease by14.5%)for BSG and from2.08%to1.84±0.01%(decrease by11.5%)for DSG.An increase in drying time from0to the time when the equilibrium was reached at the steam velocity of0.66m/s caused the starch to decrease from7.49%to 5.84±0.12%(decrease by22%)in BSG samples and from2.50%to1.93±0.05%(decrease by23%)in DSG samples.The high drying temperatures and the initially high moisture content of the spent grains are probably responsible for the partial gelatinization of starch and the formation of amylose–lipid complexes or resistant starch or both.The last two phenomena most likely ac-count for the decrease in the amount of starch measured in the samples.In general,b-glucans were affected very little by the drying processes.Only the drying tempera-ture had a small influence on the b-glucan content in the dried DSG samples;it decreased from 1.62%to 1.44±0.02%(decrease by11%)when the temperature used for drying the samples to the equilibrium changed from110to180°C.The relatively low precision (±2.30%)of the method used for determining pentosans hindered somewhat the interpretation of the results. Nevertheless,it appears that the contents of pentosans in DSG and BSG were not affected to any great extent by the drying processes.The proteins in both spent grains were likely denatured during the drying processes, but this did not affect their measured average content (including both active and denatured proteins)in dried BSG or DSG.6.ConclusionsA modified PageÕs equation was developed for describing the thin-layer drying of spent grains in super-heated steam(SS).The equationfitted the experimental data well.At the beginning of the drying,a small amount of moisture was gained on the sample surface from steam condensation.The moisture gain increased the initial moisture ratios of the samples to the range between 1.00and 1.20for BSG drying or between 1.00and 1.30for DSG drying.It decreased linearly with an in-crease in steam temperature and/or velocity.Unlike hot-air drying,not only the temperature but also the velocity of drying medium had a significant ef-fect on the thin-layer drying of spent grains in SS.Increasing the steam velocity increased the drying rate nearly linearly and consequently decreased the drying time.At145°C,an increase of steam velocity from0.3 to1.1m/s caused the drying time for reaching the equi-librium to decrease by57%for BSG drying and56%for DSG drying.Drying in SS had rather a small effect on the change of the nutrients in BSG and DSG samples.Steam veloc-ity had no noticeable effect on nutrients in dried samples.Increasing drying temperature from110to 180°C gelatinized more starch and decreased starch content in BSG by14.5%and in DSG by11.5%.No change was observed in b-glucan,pentosan,and protein contents in the dried samples.AcknowledgmentThe study wasfinancially supported by the Natural Sciences and Engineering Council of Canada. 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