cassava starch prod vietnam

Guillaume Daa, b, c

Dominique Dufoura, d

Claude Marouzéa

Mai Le Thanhb

Pierre-André Maréchalc

a CIRAD, UMR 95 Qualisud,Montpellier, France

b HUT, IBFT,Hanoi, Vietnam

c ENSBANA-UB,GPMA, EA 4181,Dijon, France

d CIAT, A.A. 6713,Cali, Colombia

Cassava Starch Processing at Small Scale inNorth Vietnam

In Northern Vietnam, small-scale cassava starch processing is conducted in denselypopulated craft villages, where processors face difficulties to expand their activities.Three different processing systems were studied among a cluster of three communesin the Red River Delta, producing up to 430 t of starch (at 55% dry matter) per day. Thefirst system, type A, is a cylindrical rasper and a manual sieve, the second, type B, is acylindrical rasper and stirring-filtering machine and the third, type C, used equipmentfor both the rasping and filtering stages. Moisture, starch, crude fibers and ash contentanalysis were carried out on samples collected from the A-B-C manufacturing pro-cesses to establish the mass balance of starch. Production capacity, water consump-tion, electrical requirements and capital-labor costs per tonne of starch (12% moisture)were also reported. A-B-C manufacturing processes enabled 75% recovery of thestarch present in fresh roots. No significant change was observed in the composition ofstarch. Upgrading from system A to B and subsequently to C resulted in an increase inthe extraction capacities (up to 0.9 t of peeled roots per hour), the extraction effi-ciencies during the extraction stage (up to 93%), and an increase in the water con-sumption and electrical power (up to 21 m3 and 55 kWh per tonne of starch, respec-tively). The highest amount of total solids carried in the waste-water was obtained withtype C (up to 17% of the dry weight of fresh roots, compared to 10% and 13% for typeA and B, respectively). This may lead to a higher chemical oxygen demand (COD) andbiological oxygen demand (BOD) in waste-water, which can result in more pollutedwaste-water than compared with the type A and B technologies. Upgrading the rasp-ing-extraction technologies also resulted in higher profits and reduction of labor pertonne of starch (up to 18 US$ and 26 man-hours respectively). The diagnosis proposedin this study can be applied in different contexts to recommend technological optionsby considering space, energy and capital-labor availabilities.

Keywords: Cassava starch; Equipment efficiency; Water uses; By-product

358 Starch/Stärke 60 (2008) 358–372

1 Introduction

In Southeast Asia the rapid economic recovery ensuredideal conditions for strengthened agricultural commoditychains. It was particularly significant for cassava (Manihotesculenta Crantz) in Thailand [1] and later on in Vietnam [2].This particular crop grown in many parts of Asia [3], iscompetitive with other starchy sources [4]. In Vietnam, thecrop yield increased dramatically in the 1990’s [5] andeventually reached the average of 15 t/ha in 2006 [6], par-ticularly with the introduction of high yield varieties [7] forindustrial purposes with new farming techniques [8]. Some

authors reported that nationwide the share of commodityproduction utilized for starch extraction was 17% in 1991[9], 24% in 1998 [10], and up to 40-70% in 2005 with thelargest portion produced in the 36 cassava processingfactories [2]. The Vietnamese Ministry of Agriculture andRural Development reported in 2005 that small-scale pro-cessing accounted for over 70% of the total units, with astarch processing capacity of less than 1 t of starch at 12%moisture wet weight basis (wwb) per day, as noted byIFPRI [10]. It has been reported that this processing scalemay last for one or two decades in Vietnam [11]. In the RedRiver Delta wet starch is produced within clusters of craftprocessing villages [12] where there is a clear divisionamong starch processors [5]. Certain households andenterprises specialize in one or a group of activities, andtogether they have a relationship that is both competitiveand innovative [13]. Despite space limitations for proces-sing activities, this model of production not only continuesto grow locally but also expands to other provinces [5].

Correspondence: Guillaume Da, ENSBANA-GPMA, Universitéde Bourgogne (UB), 01 Esplanade Erasme, Dijon, France, Phone:133 3 80 39 66 99, e-mail: [email protected] and Domini-que Dufour, Centro Internacional de Agricultura Tropical (CIAT),Apdo Aéreo 6713, Cali, Colombia. E-mail: [email protected].

© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.starch-journal.com

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DOI 10.1002/star.200800202

Starch/Stärke 60 (2008) 358–372 Cassava Starch Processing at Small Scale in North Vietnam 359

From a technological perspective, examining processesat both large or small scales indicates that there is diver-sity in cassava starch manufacturing [14]. The processingyield (kg of recovered dry starch divided by 100 kg of freshroots), consumption of water and possible electricalrequirements have been reported in previous diagnoses[15]. The processing yield range from 17% in Ivory Coastand in Colombia [16], 21% in Brazil [17] and up to 25% inThailand [1]. Water consumption per kilogram of starchwas reported to be in the range 21-40 L in Brazil [18], 30 Lin India [19], or up to 50 L in Colombia [20, 21]. Electricalenergy requirements per tonne of starch ranged from 14kWh and 21 kWh in small- and medium-scale units inIndia [22]. Despite these figures revealing potential differ-ences between processes, they remain difficult to com-pare because of the use of different methodologies toestimate their components. This study proposes a diag-nosis where a range of selective measurements areapplied to cassava wet starch processing units in North-ern Vietnam. The objectives consist of counting andcharacterizing the processing units within a cluster ofthree processing communes, and by taking into accountthe following parameters: number of processing days peryear, material balance, starch yield, water and electricalconsumption, labor, capital investment, equipmentdepreciation, and production costs. The objective is tonot only assess the different technologies used locally,but to develop a method of comparison that can beexpanded to other starch manufacturing processes inother contexts.

2 Materials and Methods

Fig. 1 shows the manufacturing process for small-scaleproduction of wet starch in Vietnam, where three differentprocessing types have been studied based on the raspingof peeled roots and starch separation. The three proces-sing types (A, B, C) are described as follows: Types A andB use a cylindrical rasping machine to crush the peeledroots (Fig. 2); however, starch separation was ensured bya manual sieve for type A or a vertical stirring-filteringreactor for type B (Fig. 3). Type C uses one machine forthe rasping and separation stages (Fig. 4).

2.1 Materials

2.1.1 Manufacturing process technologies

This study was conducted with stakeholders in cassavaroot processing for wet starch production in a cluster ofcraft hamlets from three adjacent communes in Hoai Ducdistrict, Ha Tay province [23]. This area adjoins Hanoi and

Fig. 1. Flow chart of cassava wet starch processing at asmall scale in Vietnam in 2006.

has the potential for market linkages [24]. Furthermore,this province has the largest production of cassava wetstarch in the Red River Delta [5] and the selected com-munes have extensive experience in trading and proces-sing cassava and cassava-based products [24].

2.1.2 Processing equipment

Washing: Washers used in this study consisted of batchoperated horizontal hexagonal iron cages (2 m3 in volume)rotated at 40 rpm. The power of the electrical engine was4 kW. Inlets placed on the edges of the cages suppliedand sprayed water onto the roots [25]. Each cage wasequipped with one hatch used to load and unload theroots onto a cement floor for brief storage prior to beingrasped.

Rasping: Systems A and B used the same type of rasper[25] which has the ability to work in a continuous manner(Fig. 2). The rasping surface consisted of a rotating solidwooden drum (23 cm in diameter and 31 cm in usedlength) and was serrated with fine wires (3 mm in height).Rasping for system C (Fig. 4) did not work continuously,rather it functioned per batch and operated in a raspingchamber (40 dm3 in volume) fed vertically from the topthrough one chute-like hopper [25]. The rasping surfaceconsisted of a horizontal disc (58 cm in diameter) made of


360 G. Da et al. Starch/Stärke 60 (2008) 358–372

Fig. 2. Cylindrical rasper (type A andB) for cassava starch processing at asmall scale in Vietnam.

Fig. 3. Vertical stirring tank reactor (type B) for cassava starch processing at a small scale in Vietnam.

Fig. 4. Rasper/extractor (type C) for cassava starch processing at a small scale in Vietnam.



wood and serrated with fine wires (3 mm in height). A pipeinlet was placed on the upper edge of the rasping cham-ber to spray water onto the peeled roots.

Extraction: The extractor for system A consisted of avertical circular basket (0.1 m3) where the pulp wasstirred by hand with water prior to being sievedthrough a cotton filter cloth (aperture of 70 mesh-210mm). The extractor for system B [25] consisted of avertical stirring axle placed in an aluminum tank(0.8 m3) flanked by two baffles which were fixed 10 cmfrom the bottom of the tank (Fig. 3). A cotton filtercloth (with an aperture of 70 mesh) was placed on thebottom screen of the extractor. The extractor for sys-tem C (Fig. 4) consisted of a vertical stirring-filteringreactor (0.1 m3 in volume). The movement of the ver-tical shaft, which held in place the rasping disc withthe two paddles used for extraction, allowed therasping and extraction stages to work simultaneously[25]. Extractor C was equipped with a cotton filtercloth (aperture of 70 mesh) and a 10 mesh (2 mm)screen. For systems B and C, intermediate tanks linedwith ceramic tiles were used between the separationand the settling stage in order to ensure a decantationof starch milk [1].

Settling and dewatering: For the three systems, twoconsecutive sieves (aperture of 70 and 10 mesh for theupper and lower layers respectively) fixed on woodenframes were used before sedimentation in settling tanks.The absorption stage occurred after collecting the yel-lowish green tint layer [26] (locally called “black starch”)on top of the wet starch after settling stage. This “freshblack starch” was discarded from the tank, and weighed.Samples were collected in triplicate and dried for analy-sis. Usually, “fresh black starch” is transferred subse-quently by processors into appropriate concrete tanks fora second settling stage, where a natural fermentationoccurs, with a reduction in pH from 6 to 4. Finally, theresulting product (“fermented black starch”) is collectedand boiled before being incorporated in the daily foodration for pigs. The viscosities of both fresh and fer-mented black starches were not studied. Sedimented wetstarch was covered with a layer of cloth and dried coalresidue (up to 12 kg/m3) in order to absorb sufficientamounts of water before being cut into blocks to bestacked up moist (45% moisture content, wwb) onto claybricks.

Water pumping: Unfiltered water was supplied for thewashing stage and was directly drawn from wells;whereas the extraction stage required filtered water pre-viously drawn and poured in a concrete tank filled withsand. For the entire process, three types of pumps wereused: One (Qmax = 70 L/min, P=0.75 kW) to draw under-

ground water (types A-B-C); one (Qmax = 260 L/min,P=0.75 kW) to pump filtered water up to the extractor(types B-C) and one (Qmax = 100 L/min, P=0.37 kW) topump starch milk from the intermediate tank into the mainsettling tank (types B-C).

2.2 Methods

2.2.1 Mass balance of the wet starchmanufacturing process

Measurements were conducted for particular stages ofthe manufacturing process (Fig. 5) depending on accessand relevance to samples throughout this process [27].The quantity parameters (weight, time) as well as qualityparameters (analysis) were then reported in detailed flowsheets in order to compare the mass balances betweenthe different processing types.

Organizing the trials and moisture content: Diagnostictrials were repeated in triplicate with the same house-holds during the 2006 season. For each trial, 15 t of highyield cassava varieties [2] were purchased and deliveredby truck. The roots were then divided within the A, B andC processing units in order to be crushed simultaneously(Fig. 5). Up to 4 kg of roots were collected from the truckdelivery, and then the roots were immediately cut intosmall pieces, mixed and dried at 607C for 48 h [28] forfurther analysis. Samples in triplicate which needed to beanalyzed were also collected from the manufacturingprocess (Fig. 5) during the 2006 harvesting season andthey underwent the same procedure. The moisture con-tent of the products which did not need further analysis,was determined by drying 10 g of sample at 1057C for 24h [29]. The amount of total solid waste carried by waste-water was measured in waste-water samples (500 mL)collected at regular intervals from the main sedimentationtank. The samples of waste-water were evaporated(without boiling), and dried at 1057C until a constantweight was reached. The difference between the weightof the empty container and the weight of the containerafter drying represented the total solids carried in thewaste water.

Water consumption measurement: The water con-sumption was measured (Fig. 5) by water meters pre-viously placed on the water inlets of the washers and atype B or C extractor. For manual extraction (type A), aderivative device system was set-up with one centrifugalpump (Qmax = 100 L/min, P=0.37 kW) and one water-meter. The volumes of suspensions (starch milk, waste-water) in the sedimentation tanks were also reported(Fig. 5).



Fig. 5. Flow chart diagram of wet starch production at a small scale in Northern Vietnam. The weightsymbol corresponds to the solid materials which have been weighed and sampled. The arrow symbolmarked ‘water’ corresponds to a water inlet where water meters were set-up. The ruler symbol cor-responds to the ruler used to measure the volume of liquid in the settling tanks.

2.2.2 Analysis

Determination of starch content: The starch content ofthe solid samples (Fig. 5) was measured using an enzy-matic colorimetric method [30]. The results are given in%of starch per kilogram of dry matter.

The starch content in the starch milk suspensions wasobtained by a density method. Two hydrometers wereused (Dujardin-Salleron, Arcueil, France, model 1000-1030 6 0.2 g 10-3 m3 and model 1000-1100 6 0.5 g10-3 m3) to measure the density (at 207C) of aliquots (0.500L) collected at regular intervals from the outlets of type Band type C extractors throughout the duration of theextraction process.

Crude fiber content: The fiber content was determinedfrom the loss of ignition of the dried residue that remainedafter the digestion of cassava flour (2 g) with 1.25%aqueous H2SO4 and 1.25% aqueous NaOH [31]. Theresults are given in% of crude fibers per kilogram of drymatter.

Ash content: The ash content was calculated after 1g ofsample was heated at 5507C for 3 h [32]. The results aregiven in% of ash per kg of dry matter.

Scanning electron microscopy (SEM): Dehydratedsamples (starch granules, cassava bagasse, black starch)were sprinkled on double-sided sticky tape, mounted oncircular aluminum stubs, coated with 35 nm of gold-alu-minum, and then photographed in a scanning electronmicroscope (JSM 820 Jeol, Tokyo, Japan) at an accel-erating voltage of 20 kV. The granule size was measured.

Particle size analysis: The sizes of starch granules andparticles in wet starch and black starch were determinedby laser diffraction analysis (Mastersizer 2000, MalvernInstruments LtD, Worcestershire, UK) with a refractiveindex of 1.53. The particle size is expressed in mean vol-ume in micrometers [33].

Electrical consumptions measurements: The studyfocused on the rasping and extraction stages which bothrequired three-phase electric power. This power wasmeasured by a current analyzer (model CA 8230, ChauvinArnoux, Paris, France) during the trials conducted in2006. The device was placed on the three phases elec-trical outlet in order to record the real power (every 5 s) ofthe rasper and the extractor while it was working.



2.2.3 Labor input and production costcalculation

The labor input and time requirements for starch manu-facturing were reported for each trial to establish the man-hours that were needed. According to the guaranteed mini-mum wage, the salary paid per hour was 2,557 Vnd (0.16US$). Variable costs were calculated by reporting inputs(raw material, electricity, labor) and outputs (final productand by-products) from processing (Fig. 5) during the pro-cessing season (October to April) for households (usingtypes A-B-C) within the three communes. Contingenciesrepresented 2% of the variable costs [18]. Fixed costs werecalculated with the cost of employment (15 years of usefullife) and equipment (six years of useful life), and by con-sidering a 10% interest. The production cost was calculatedbased on 1 t of starch at 12% moisture content (wwb).

2.2.4 Calculation and statistical analysis

From the mass balance and composition analysis, the fol-lowing yield components have been calculated: the pro-cessing yield, the overall starch recovery (kg of starchrecovered divided by kg starch in fresh roots [18]), the rasp-ing effect (described by Grace [26]) and the starch extractionefficiency (kg of starch liberated divided by kg of starch inwashed roots [18] or the fraction of starch released in disin-tegration [15]). Statistically significant differences between

sample meanswere determined using the Student’s t-test orANOVA test for multiple comparisons at a 95% confidencelevel. The statistical analyses were performed with Statisticav7.1 software (Statsoft, Inc., Maisons-Alfort, France).

3 Results

3.1 Production characteristics

3.1.1 Variability of the quality of raw material

The quality of the fresh roots for processing starch depend-ed on the dry matter content of the roots (Fig. 6). This resul-ted in different levels of starch content, which is known to beclosely correlated not only to the apparent density [34, 35]but also to the dry mattercontent of the roots [28, 36]. Duringthe trials, the roots had a dry matter content, crude fibercontent and starch content in the range of 38.9-44.3%, 2.3-3.9%, and 80.6-84.7%, respectively. The lowest values indry matter and starch corresponded with the end of theprocessing season, when the rainy season started (April).

3.1.2 Distribution of the processing types

The survey carried out in 2005 (Tab. 1) showed that thedistribution of the types of processing was different fromone commune to another; with a tendency (from 2005) to

Fig. 6. Distribution of the dry matter content of the cassava fresh roots used for wet starch processingat a small scale in Vietnam (2006-2007).



Tab. 1. Distribution of the three types of technologieswithin the surveyed communes in 2005 in Viet-nam.

Commune Number ofhouseholdsproducingwet starch

Distribution ofhouseholds types

A[%]

B[%]

C[%]

Duong Lieu 514 2 75 23Cat Que 184 58 36 6Minh Khai 35 0 71 29

switch from type A to type B and subsequently to type Cprocessing types. This evolution has been mainly moti-vated by increasing the producing capacities and reduc-ing the labor input [23].

3.2 Mass balance of wet starch

3.2.1 Balance sheet of wet starch

The calculation of the mass balance (Tab. 2) resulted indifferent coefficients of variation. Peels and black starch(in the range 22-46%) demonstrated that they havebeen affected by the fluctuation of the quantity of dirton the roots. Consequently, the calculation of the massbalance can be achieved by weighing only peeled roots(or cassava pulp), cassava bagasse and wet starch,which all corresponded to low variation coefficients(1.8%, 7.4% and 4.9%, respectively). Furthermore, themass balance of type C (Tab. 2) revealed that thegreater quantity of dry matter liberated during theextraction stage was followed by a greater amount oftotal solids carried in the waste-water compared withthe A and B types.

3.2.2 Production yield components

There were no statistically significant differences for theprocessing yield (overall average of 25.8 6 1.6) betweenthe three systems; which therefore confirmed the simila-rities already observed in starch recovery (Tab. 2). Theother yield components (Tab. 3) showed that the type Cextraction was more efficient than the type A and B tech-nologies. The starch recovery for type C was not limitedby the extraction stage, but possibly by the sedimentationprocess where there were higher amounts of total solidscarried in the waste-water (Tab. 2). This could be con-firmed by investigating the size distribution of the starchgranules that remained in the waste-water for each pro-cessing type.

Tab. 2. Balance sheet for the cassava starch manu-facturing process at a small scale in Vietnam in2006 (kg of dry weight).

Material Type A[kg]

Type B[kg]

Type C[kg]

Fresh roots 100 100 100Peeled roots 98.4 6 1.1a 97.6 6 1.8a 97.8 6 1.7a

Peels, dirt 1.6 6 0.4a 1.5 6 0.4a 1.5 6 0.7a

Cassava bagasse 21.4 6 1.6a 20.1 6 0.1a 13.8 6 1.0b

Black starch fraction 3.1 6 0.8a 3.6 6 1.5a 3.3 6 1.1a

Wet starch 63.5 6 2.9a 62.2 6 3.1a 64.8 6 0.8a

Total solids carriedin waste-water

10.4 6 1.3a 12.6 6 2.1a 16.5 6 1.9b

The data provides the average of three trials conductedfrom January to March 2006 (processing season). Thestandard deviations are indicated with a “6” sign. Withineach line, statistically significant differences at a = 5%level are indicated with superscript letters (e.g., a, b).

Tab. 3. Yield components for three types of cassavamanufacturing processes from Vietnam at a smallscale in 2006.

Yield components A[%]

B[%]

C[%]

Processing yield 25.4 6 1.5a 25.0 6 1.1a 27.0 6 1.7a

Overall starchrecovery

74.4 6 3.9a 73.3 6 4.0a 76.1 6 1.9a

Rasping effect 85.1 6 0.3a 85.0 6 2.2a 93.1 6 0.9b

Starch extractionefficiency

86.3 6 1.5a 87.3 6 3.9a 92.6 6 0.7b

The data provides the average of three trials conductedfrom January to March 2006 (processing season). Thestandard deviations are indicated with a “6” sign. Withineach line, statistically significant differences at a = 5%level are indicated with superscript letters (e.g., a, b).

3.2.3 Water consumption

A high variation coefficient in water consumption for thewashing stage was observed (Tab. 4). It revealed that,depending on the contamination level of dirt and soil onthe fresh roots, different levels of water were required toensure a proper cleaning and low ash content in the finalproduct [1]. The lowest water consumption without recir-culation was obtained with the type B extraction (Tab. 4).The volume of water per kilogram of starch was lowerthan at a similar scale or equivalent than at a large scalewith recycling water process; where 22 L [37] and 10 L [1]have been reported respectively. The higher water con-sumption for type C versus A and B was due to the use of



Tab. 4. Water-consumption for types A, B and C at a small-scale in Vietnam in 2006 (L/kg of starch at12% moisture content, wwb).

Processing stage A[L/kg]

B(no recirculation)[L/kg]

B(recirculation)[L/kg]

C[L/kg]

Washing 2.0 6 0.9(****) 2.0 6 0.9(****) 2.0 6 0.9(****) 2.0 6 0.9(****)Rasping 0.0 6 0.0(***) 0.0 6 0.0(***) 0.0 6 0.0(***)Extraction 14.0 6 0.4c(*) 11.1 6 0.6b(**) 7.9 6 0.3a(**) 18.8 6 0.4d(**)Total 16.0 6 0.4c 13.1 6 0.6b 10.0 6 0.3a 20.8 6 0.4d(**)

Average and standard deviation obtained from 4 trials (*), 6 trials (**), 8 trials (***), 11 trials (****) con-ducted from January to December 2006. The standard deviations are indicated with a “6” sign.Within each line, statistically significant differences at a=5% level are indicated with superscript let-ters (e.g., a, b, c, d). The data which is similar along the same line corresponds to the samemeasurement. The data reported for type C during the extraction stage includes the volume of waterused for both rasping and extraction stages which worked simultaneously.

water for both the rasping and extraction stages (Fig. 4),where 6.1 ( 6 0.1) and 12.7 ( 6 0.1) L/kg starch weresupplied through the upper water inlet (simultaneousrasping-extraction phase) and through the lower inlet(extraction phase without rasping).

3.2.4 Quality of the products

The process did not allow for the extraction of the wholequantity of starch that was previously contained in theparenchyma of the roots (Fig. 7) for all three systems A, Band C. The composition of the cassava bagasse revealedthat the starch content was significantly higher for types Aand B as compared to type C; with a 54.0% (62.8), 58.7%(63.2) and 41.2% (63.2) respectively. The crude fiberscontained in types A and B bagasses were significantlylower than in type C; with a 15.7% (61.0), 14.9% (61.2)and 21.4% (61.8) respectively. The ash content of thebagasses from types A, B and C were not indicativelydifferent and were in the range of 1.3-2.2%. “Fresh blackstarch”, a concentration of insoluble material during thesettling stage, was mainly composed of 61.2% starch,10.2% (60.1) proteins, 6.9% (60.2) fat, 2.0% (60.1) ashand 0.74% (60.01) f crude fibers. The low proportion of“fresh black starch” obtained in the mass balance (Tab. 2)is relevant with what is known on the low levels of proteinscontained in cassava roots (less than 1%). Furthermore,“fresh black starch” (Fig. 7) shows both small particles(possibly starch granules of less than 10 mm in diameter)and small globular clusters allocated to the proteins lib-erated with starch during the extraction phase. The wetstarch composition did not show significant differencesbetween the three types, neither in starch (97.0%60.16),nor in crude fibers (0.15%60.08) nor in ash content(0.21%60.12). The great variation coefficients within the

different components indicated that the determination ofthe composition was not sufficient to characterize thedifferences between A-B-C starches, like previouslynoted elsewhere [1, 28]. The mean volume of the starchgranules in wet starch was 24.15 mm (62.81).

3.3 Equipment efficiency

3.3.1 Rasping and extraction characteristics

Small differences have been noted between cylindricaland disc raspers (Tab. 5) in terms of surface or used linearspeed (corresponding to the region of the rasping discwhere rasping is supposed to occur, at a 0.75 radius). Themain difference is that the type C extractor required waterto drag the fresh pulp down the extracting chamber(Fig. 4). The contact surface between the pulp and thesieve remained lower than in the type B extractor; how-ever the type C pulp material in contact with the sievingsurface was stirred three times more frequently than thetype B pulp material (Tab. 5).

3.3.2 Production capacities

The washing times (Tab. 6) varied as a result of the quan-tity of dirt and peels that were needed to be removed.With the introduction of mechanical washers, this stageno longer limited the capacity of the process, as was tra-ditionally the case at this scale [22, 38]. Despite the use ofiron cages, which are still required for half the time duringthis stage in order to load and unload the roots, the ca-pacity remained slightly greater than those reported inColombia (1,000 kg/h), where loading is facilitated by theplant design utilizing gravity [21]. The capacities obtainedwith the cylindrical rasper (Tab. 6) and the rasping disc



Fig. 7. Up: Starch granules in cassava pulp before extraction (left) and in cassava bagasse afterextraction (right). Down: Starch granules (left) and black starch fraction (right).

Tab. 5. Performances of raspers and extractors in Viet-nam.

Parameters Type of rasper Type of extractor

Drum Disc B C

Rotation per minute[rpm]

4,400 2,400 140 2,400

Linear speed on theedge

[m/s]

50.7 72.8 8.6 57.8

Used linear speed[m/s]

50.7 54.6 6.9 49.9

Rasping surface[m2]

0.21 0.23 – –

Sieving surface[m2]

– – 1.24 0.22

Surface6contacttime

[m2]

15.7 9.31 5.8 17.6

(1,039 6 39 kg/h) were not significantly different and bothtechnologies were limited by the manual loading time,which equaled the time to load the roots into the washer.

The drop in the extraction capacities of both systems Aand B (Tab. 6) depended mainly on the technologies used.The type C extraction did not require loading and itshigher capacity, which almost equaled the capacity of theprevious stages (Tab. 6), was characterized by a greatervelocity of the blades (Tab. 5) as compared with the type Bextractor. The settling and dewatering capacities weresimilar for the three systems A, B and C in a range of 61-91 kg/h of fresh roots. No significant innovations havebeen reported locally to speed up the starch settling dur-ing sedimentation.

3.3.3 Comparison of extraction systems

The extraction stage lasted for 4, 61 and 2 min for pro-cessing 8, 220 and 14 kg of dry pulp per batch for A, Band C, respectively. Therefore, the A and C extractorsrequired 29 and 15 batches, respectively, in order toextract the equivalent amount of starch extracted in onebatch for the type B extractor. Currently, the amount ofwater used for type B extraction has been reduced byrecycling the suspension milk (Fig. 8) whenever the den-sity of the starch slurry reaches 1010 g 10-3 m3 (1.47Bé).



Fig. 8. Starch milk density profile during type B extraction (left) and type C extraction (right) from Vietnam. The symbol “ ”corresponds to the experimental point (average of triplicates samples with repeated trials) with standard deviation.

Tab. 6. Capacity (kg of entering material per hour) ofwashing, rasping and extraction stages duringthe cassava wet starch manufacturing process in2006 in Vietnam.

Processingstage

Processing types

A[kg/h]

B[kg/h]

C[kg/h]

Washing 1,140 6 106 1,140 6 106 1,140 6 106Rasping 1,053 6 192c 1,053 6 192c

Extraction 273 6 34a 410 6 46b 864 6 83c

The data provides the average of three trials conductedfrom January to March 2006 (processing season). Thestandard deviations are indicated with a “6” sign. Statis-tically significant differences at a=5% level are indicatedwith superscript letters (e.g., a, b, c). The data which issimilar along the same line corresponds to the samemeasurement. The data reported here for type C at extrac-tion stage includes the capacity obtained for both raspingand extraction stages which worked simultaneously.

The slurry is poured in an intermediate tank before beingused at the beginning of the next batch. This correspondsto a 29% (63) reduction of the total water used comparedto normal extraction with the same reactor.

3.3.4 Energy consumption

During the normal operation of the cylindrical rasper(Fig. 2), operators pushed the roots manually on the

Tab. 7. Comparison of electrical requirements betweenthree types of cassava processing systems forproducing 1 t of commercialized Starch (at 12%moisture content, wwb) in Vietnam in 2006.

Parameters Cylindricalrasper(types A-B)

Front sievingextractor(type B)

Rasper –extractor(type C)

Engine power[kW]

15 3 15

Real power consumption[kW]

10.4 (62.0) 2.3 (60.4) 13.0 (64.6)

Electrical energy[kWh/t]

19.8 10.6 55.3

The standard deviations are indicated with a “6” sign.

rasping surface to increase the rasping efficiency andrasping capacities (up to 1,789 kg/h). This resulted in aheterogeneous demand of power (Tab. 7) with a max-imum of 16.2 kW, which made the engine capacity suit-able for this stage. By using the rasping disc, the operatorlimited manual hazard risks. High variation coefficients inpower consumption were obtained (Tab. 7) where thehighest demand in power (25 kW maximum) occurredduring the rasping stage. The minimum power (3.9 kW)corresponded to the time (5 s) when the operator emptiedthe cassava bagasse after extraction. A high demand inthe number of three-phases of the electrical units (Tab. 7)could have resulted from a greater velocity of the raspingdisc (Tab. 5) rather than the rasping cylinder. Thus, con-sidering an engine yield of 75% to convert electricalenergy into mechanical energy, the measurement of the



type C equipment revealed that 40% of the mechanicalenergy was used for rasping and 60% was used forextraction. This suggests that both types of raspersrequired similar levels of power; however, a higher level ofelectrical power was required for type C extraction ascompared to type B (Tab. 7). The type B extractor requireda maximum real power of 3.4 kW at the end of the pro-cess, when the fibrous residues became dryer. The ca-pacity of the engine of 3 kW was efficient and the averagemechanical power required for this stage was 1.6 kW.

3.5 Labor requirement

For the past ten years, investments in new equipment(rasping disc, stirring machines) have been consistentwith the household objectives to reduce labor [23] from 31to 15 and subsequently to 4 man-hours (Tab. 8) for therasping and extraction stages from types A, B and C,respectively. The conservation of former technologies forthe preparation stages (root transportation, sorting andwashing) as well as for the sedimentation stage (Tab. 8)has resulted in a strong limitation for man-hour reduction.Slight labor reductions occurred by increasing capacitiesof settling tanks for type C (Tab. 8), however, the lack ofspace (population density up to 3,000 inhabitants persquare kilometer) restricted the households to expandthese capacities, to switch to settling tables [14], oreventually to settling canals [21] usually used at this scale.Capacities and labor reduction have increased dramati-cally by investing in separators and centrifuges at a largescale [1], but these solutions have not been studied inVietnam for small-scale wet starch processing. In order tomeet specific demands, such as high quality starch forpharmaceutical products, some centrifuges importedfrom China have recently been used within the clusters bystarch refiners.

3.6 Production cost

The production cost for 1 t of starch was 166, 165 and 162US$ for types A, B and C, respectively (Tab. 9). Main costswere from raw materials which accounted for 88-90% ofthe total production cost for 1 t of cassava starch. Pro-cessing costs (labor and electricity) were reduced to aminimum, and in the range of 5-7% of the productioncosts (Tab.9). Upgrading the technology to type Crequired higher investment costs for equipment and vari-able costs (electricity); however, it resulted in an economyof scale (Tab. 9), as previously reported in a comparativestudy between graters in Nigeria [39]. The cost calculationtakes into consideration that labor for the processingwork is compensated; however it is rarely the case be-

Tab. 8. Labor input for 1 t of starch (at 12% moisturecontent, wwb) production in small-scale cassavastarch industries in Vietnam in 2006 (man-hours).

Unit operations Processing types

Type A[Mh]a

Type B[Mh]a

Type C[Mh]a

Reception of fresh roots 3.8 3.8 3.8Washing the fresh roots 4.6 4.6 4.6Sorting and Transferring the

peeled roots to rasping3.2 3.2 3.2

Rasping 3.6 3.6 1.6Transporting the pulp 5.3 5.3 0.0Extraction 22.0 6.4 2.5Settling and drain off 12.9 12.9 6.9Dewatering and cutting 3.7 3.7 3.0Total 58.7 43.8 23.2

Mha = man-hours.

cause each processing unit usually operates within thesame household. So, starch manufacturing at small scalehas not only been profitable (Tab. 9), but also represents alocal employment opportunity [40].

4 Discussion

The future of producing starch at a small scale was limitedin Vietnam in 1999 [41]; however, the capacity to expandthis activity has been revealed in this study and can beachieved by substituting capital investments for laborreduction. From a technological perspective, rasping-extraction (type C) resulted in increasing process effi-ciency with low quantities of starch contained in cassavabagasse compared to other extraction technologieslocally or elsewhere [42]. This could be attributed to betterrasping efficiency, followed by better extraction efficiency,in order to liberate the starch granules trapped in the net-work of fibers. Furthermore, greater capital-intensiveproduction methods continue arising such as new mobilecontinuous washers, which can be fed from the bulkdelivery and then directly connected to the rasping-extracting machine [25]. Despite making investments forthe new washing technology which may result in thecontinued optimization of the capital and labor for pro-duction [43], it may require a greater source of electricity,which can be a constraint to extend these technologies inthe future either to other rural areas in Vietnam or even-tually to other developing countries.

The processors, however, endure remaining issues tomaximize starch production. Firstly, the sedimentationstage is still a bottleneck for the manufacturing process.



Tab. 9. Cost structure, profit and income generation of small-scale units for one month in Vietnam(2006).

Items Unit Type A Type B Type C

Quantity Value[US$]

Quantity Value[US$]

Quantity Value[US$]

Starch [t] 10 1,714 9 1,657 19 3,381By-product [t] 3 43 3 42 5 85

1 Total returns [month] 1 1,757 1 1,699 1 3,4672 Raw material [t] 33 1,431 32 1,383 66 2,7953 Electricity [month] 0 16 0 24 0 90

Contengencies [month] 1 31 1 29 1 594 Fixed costs [month] 1 51 1 60 1 965 Laborers [Mma] 1 92 1 66 1 796 Production costs [month] 1 1,621 1 1,562 1 3,1197 Profit [month] 1 136 1 137 1 3488 B/C ratio [month] 1 1.08 1 1.09 1 1.119 Income generation [month] 1 228 1 202 1 427

Profit equals to total returns (1) minus production costs (6). B/C ratio (8) corresponds to total returns(1) divided by the subtraction of (1) and (7). Income generation (9) is the addition of (5) and (7). Mma =man-months. Starch is at 12% moisture content wwb.

Some options such as concentrating the starch milk byusing hydrocyclones [44, 45] or using the “sour liquid”method similar to the sweet potato starch production inChina [46, 47], could be investigated locally to reduce thesettling time [48, 49]. Secondly, waterconsumption remainscritical for the manufacturing process. This study showspromising results on the reduction of water consumption byre-circulating starch milk during extraction with Type B. Al-though it resulted in a reduction in the quantity of watercompared to the other types (A, C) this reduction remainslower than the 50% announced by processors who usehydrocyclones at similar scales [44, 45]. Thus, the possibil-ity of re-circulating starch milk with system C or developinga continuous rasping-extractor might be additional oppor-tunities to investigate. Thirdly, each household usually digsan individual well to pump ground water up to 80 m, and thewaste-water (converted from the water consumed in theextraction stage) is then discharged from the settling tankswithout treatment, as previously reported in Colombia [50,51] or in India for sago starch [45]. The potential of waste-water as a nutrient-rich irrigation source for rice was eval-uated at a small-scale in Vietnam [52], however, it has notbeen applied locally. Thus, this study shows greater pro-duction capacities with type C processing as a result ofgreater amounts of total solids carried in the waste-water.Consequently, particular attention must be paid on thewater treatment by upgrading the technologies to type C.Households have limited space and therefore using bio-ponds may not be a practical option to advocate for waste-water treatment. [53]. Consequently, the treatment ofwaste-water may be investigated locally through more

economical solutions like anaerobic horizontal flow filtersresulting in biogas production, such as in the case ofColumbia where promising results are evident [54].

Finally, wet starch is commonly used directly for specificlocal demands [52, 55], and eventually it is stored underanaerobic conditions where its quality is subject tochange [56, 57] before being reprocessed locally (afterone year). With the new development of large scale units[5, 58], small-scale processors face a new challenge toreach quality standards required by end-users unless wetstarch production becomes an intermediate scale prod-uct to reduce costs for further large-scale processing(purifying, drying, packaging) as reported previously inChina [59]. It is important to note the distance betweenharvesting to processing (up to 200 km), which results innumerous transaction costs [5], and restrict potentialprice reduction for raw materials. In the production cost,these account for higher shares compared to other loca-tions, either at a small scale [60] or at a large scale [1].Moreover, from 2006, the high demand for cassava chipsin China or starchy sources for bioethanol productionresult in an insufficient raw material supply for all starchprocessors [61] who have to handle a great variability ofthe quality of the roots.

5 Conclusion

The methodology of diagnosis proposed in this studyapplied to cassava wet starch, allowed the assessment of



manufacturing units at a small scale in Vietnam. Theresults revealed that this production scale showed higherefficiency than similar scales in other locations. The maindifferences between the three processing types, whichdiffer in the rasping and extraction stages, were in ca-pacities, water consumptions, electrical requirementsand capital-labor costs, with a tendency in adopting con-tinuous processes for washing and rasping stages. Fur-ther capacity expansion for processors might be allowedby developing continuous rasping-extraction stages withhigher concentrations of starch milk in order to overcomehigh local constraints on space limitation. A com-plementary study on socio-economic aspects (value-chain mapping, customer’s need on starch quality,access to credit) would help to better understand theorganization of the production of wet starch. Finally, themethodology of diagnosis presented in this study can beused as a basis for other foodstuffs produced locally(canna or kudzu starch) or elsewhere (sweet potatostarch) to supplement information for rural developmentissues.

Acknowledgements

The work reported in this study was supported by theCentre de Coopération Internationale en RechercheAgronomique pour le Développement (CIRAD) as well asHanoi University of Technology (HUT) and the Universityof Burgundy (ENSBANA-UB). We also acknowledge Dr.Thierry Tran (Cassava and Starch Technology ResearchUnit, CSTRU, Kasetsart University, Thailand) and TerezaSanchez (Centro Internacional de Agricultura Tropical,CIAT, Colombia) for analysis. The authors are thankful forDr. Dai Peters (CIAT), Loan Trinh Thi Phuong and NguyenKhac Quynh (Vietnamese Agricultural Academy of Sci-ence, VAAS) for their help on craft villages.

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(Received: January 3, 2008)(Revised: March 6, 2008)(Accepted: March 20, 2008)


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