The International Development Research Centre is a public corporation created by the Parliament of Canada in 1970 to support research designed to adapt science and technology to the needs of developing countries. The Centre's activity is concentrated in five sectors: agriculture, food and nutrition sciences; health sciences; information sciences; social sciences; and communications. IDRC is financed solely by the Government of Canada; its policies, however, are set by an international Board of Governors. The Centre's headquarters are in Ottawa, Canada. Regional offices are located in Africa, Asia, Latin America, and the Middle East. © 1978 International Development Research Centre Postal Address: Box 8500, Ottawa, Canada KlG 3H9 Head Office: 60 Queen Street, Ottawa Weber, E. J. Cock, J.H. Chouinard, A. IDRC Centra Internacional de Agricultura Tropical (CIA T) IDRC- l l 4e Cassava harvesting and processing: proceedings of a workshop held at CIAT, Cali, Colombia, 24-28 April 1978. Ottawa, IDRC, 1978. 84 p. /IDRC publication/. Report of a workshop on /cassava/ /harvesting/ and /food processing/ - discusses /feed production/, /drying/ /food technology/, effects of chip size and shape; /starch/ extraction, use of cassava /flour/ in /food preparation/, cassa va /fermentation/ for /fuel/ /alcohol/ production. /List of participants/. UDC: 633.68 ISBN: 0-88936-188-6 Microfiche edition available IDRC-114e Cassava Harvesting and Processing Proceedings of a workshop held at CIA T, Cali, Colombia, 24-28 April 1978 Editors: Edward J. Weber, 1 James H. Cock, 2 and Amy Chouinard 3 C osponsored by the International Development Research Centre and the Centra Internacional de Agricultura Tropical, CIA T 1Senior Program Officer, Agriculture, Food and Nutrition Sciences Division, Latin American Regional Office, International Development Research Centre, Bogota, Colombia. 2Leader, cassavaprogram, CIAT, Cali, Colombia. 3Editor, Communications Division, International Development Research Centre, Ottawa, Canada. Contents Foreword Edward J. Weber and James H. Cock 3-5 Participants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Cassava Processing in Southeast Asia Robert H. Booth and Douglas W. Wholey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-11 Cassava Processing for Animal Feed Rupert Best 12-20 Cassava Chipping and Drying in Thailand N.C. Thanh and B.N. Lohani ............................................ 21-25 Small-Scale Production of Sweet and Sour Starch in Colombia Teresa Salazar de Buckle, Luis Eduardo Zapata M., Olga Sofia Cardenas, and Elizabeth Cabra ...................... 26-32 Large-Scale Cassava Starch Extraction Processes Bengt Dahlberg 33-36 Cassava Flours and Starches: Sorne Considerations Friedrich Meuser . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 7 -40 Alcohol Production from Cassava Tobias J.B. de Menezes Prospects of Cassava Fuel Alcohol in Brazil Wilson N. Milfont Jr Use of Fresh Cassava Products in Bread Making Joan Crabtree, 41-45 46-48 E.C. Kramer, and Jane Baldry ........................... 49-51 Harvesting: A Field Demonstration and Evaluation of Two Machines David C. Kemp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53-57 Follow-up Evaluation of Two Harvesting Machines Dietrich Leihner ........................................ 58-59 Agronomie Implications of Mechanical Harvesting James H. Cock, Abelardo Castro M., and Julio Cesar Toro ................. 60-65 Economie Implications of New Techniques in Cassava Harvesting and Processing Truman P. Phillips ........................ 66-74 Discussion Summary 75-78 References 79-83 Foreword Cassava is a very efficient producer of carbohydrates even where soi! is poor and rainfall uncertain; millions of people in many parts of the world grow it and depend on it as a major source of energy. Yet, until recent years, little research had been carried out to improve the crop. In the early l 970s, two international agricultural research centres - Centra Internacional de Agricultura Tropical (CIA T) in Colombia and the International Institute of Tropical Agriculture (IIT A) in Nigeria - identified cassava as a major research focus. Subsequently, the International Development Research Centre (IDRC) of Canada has collaborated with both of these institutions to promote the development and utilization of cassava through jointly sponsored workshops, studies, and publications; this report is the latest in the series. It is based on a workshop held at CIAT 24-28 April 1978. Previous works have been published irregularly since 1972 when the first seminar was held. At that time, a group of scientists who possessed the broadest and most up-to-date information on the crop met to define a series of problems to be investigated and to identify priorities. Among others, their discussions prompted more intensive research into the problems of hydrocyanic acid toxicity resulting from cassava ingestion and the causes and contrai of cassava mosaic disease found principally in Africa. Shortly thereafter, a study was commissioned on cassava utilization and potential markets. In 1974, the problems associated with processing, storing, and handling cassava after harvesting were considered at a workshop in Thailand and the proceedings published. Also in 1974, a review of early research findings and ideas was published in the booklet, Current Trends in Cassava Research. Then, because cassava research was developing rapidly throughout the world, two forward-looking workshops were organized to study the international exchange and testing of cassava germ plasm. Held at CIA T and IITA, the workshops established standard procedures for handling improved cassava germ plasm and introducing it into producing areas. Also, it was realized that strong national programs in cassava-producing countries are essential for adapting research centre findings to local conditions; as a result, a booklet proposing an international research network for cassa va was published. The etiology and contrai of two major diseases of cassava, African cassava mosaic and cassava bacterial blight, were the subject of workshops in 1976; in 1977, a meeting was held in Guelph, Canada, dealing with cassava as an animal feed. This series of reports and meetings, although important in summarizing a great deal of information, represents only part of the knowledge that has been accumulated over the last 6 or 7 years. There exist many other published and unpublished papers and research reports from CIAT, IITA, and other institutions around the world, and the network of cassava research is growing very rapidly. Tremendous advances have been made in techniques for managing and growing cassava, and remarkable increases in production will be possible in the near 3 future. These increases will be based on better technology, such as disease and pest control, better varieties, etc., as well as on the opening up of large new land areas for cassa va production made possible by this improved technology. It appears that a crucial moment in the evolution of cassava production and utilization has been reached. In 1974, Phillips' study on cassava use and marketing showed that demand for cassava could be expected to exceed supply for some time to corne. At present, however, per capita cassava consumption is dropping. The reason is primarily the cost of production, especially where yields are low and traditional production methods are used. Cassava is extremely perishable and must be either consumed or processed within a few days of harvest. It is bulky, heavy, and expensive to transport over long distances. As a result, the crop is largely consumed in rural areas and has not greatly penetrated large urban markets. This situation has important policy and investment implications and unless more attention is given to resolving harvesting and processing constraints, the large potential increases in production will not be realized. In this context, the present workshop was organized to review current harvesting and processing technology and to address some of the major improvement issues. The meeting began with a presentation on cassava chipping, pelleting, and drying in Southeast Asia, presented by Robert Booth, followed by a paper on processing cassava for animal feed by Rupert Best. The former described current practices, and the latter reported recent research on more efficient methods for cassava drying. Another paper by N.C. Thanh and B.N. Lohani described research findings from Thailand on different drying techniques, incl.uding the effects of chip size and shape. Three papers on cassava starch and flour production were presented in the second session: Bengt Dahlberg commented on large-scale starch extraction processes and machinery; Teresa Salazar de Buckle dealt with small-scale starch extraction processes in Colombia; and Friedrich Meuser summarized some major considerations in cassava starch and flour processing. In the following session, Joan Crabtree presented findings on the use of fresh cassava in bread making. Next, Tobias B. de Menezes elaborated the technical processes of alcohol manufacture from cassava and summarized Brazil's ambitious alcohol production program, the economics of which were detailed by Wilson Milfont Jr. The alcohol production papers are of particular interest at this time when petroleum energy supplies appear limited; they were followed by presentations defining research priorities and policy implications. The first, presented by James Cock, dealt with the agronomie implications of cassava harvesting and processing technology, and the second, by Truman Phillips, carefully analyzed the economic implications of new cassa va technology. The papers and discussions were followed by a field trip that gave the participants a firsthand look at two cassava harvesting machines. These machines were of different types: one, a harvesting aid developed at CIA T; the other, a full-scale harvester. The latter was kindly provided by Richter Engineering of Australia. David Kemp, Ayob Sukra, and Winston Harvey, engineers attending the workshop, evaluated the machines' performances; their findings are included in this publication as a special rnport. A follow-up evaluation by Dietrich Leihner is also included. Special thanks are extended to Dietrich Leihner and Alphonso Diaz of CIA T for their considerable efforts in organizing the field day and machinery demonstration. Each topical session of the workshop was followed by a discussion period 4 opened with comments by a session rapporteur. The information presented in the final section of this publication is a summary of the rapporteurs' reports. We are grateful to Ayob Sukra, Friedrich Meuser, Wilson Milfont Jr, Julio Cesar Toro, and John Lynam, who willingly served as rapporteurs, for their valuable contribution. The workshop highlighted the need for integrating production with utilization and, for the first time in the series of meetings, scale of operations was of considerable concern. To date, knowledge on cassava has generally been limited and compartmentalized, and research has been geared to gaining more basic knowledge of the crop. Now that improved production technology has reached a level where it can be used to increase farm yields, consideration of the potential social and economic impact of this new technology is imperative. Although the field production technology appears to be adaptable for use by either small or large farmers, efficient mechanical harvesting and processing of the crop is likely to be easier for the large producer. Hence, in the improvement and application of harvesting and processing technology, great care must be taken to en sure that new developments do not favour only large producers who may, due to more efficient, large-scale harvesting and processing, cause severe economic problems for small producers. 5 Edward J. Weber and James H. Cock Participants Rupert Best, Grupo de Politica Tecnologica, Acuerdo de Cartagena, Casilla de Correo 3237, Lima, Peru. Robert Booth, Centro Internacional de la Papa, Apartado Aereo 5969, Lima, Peru. Abelardo Castro, Centro lnternacional de Agricultura Tropical (CIA T), Apartado Aereo 67-13, Cali, Colombia. Amy Chouinard, International Development Research Centre (IDRC), Box 8500, Ottawa, Canada KlG 3H9. James Cock, Centro Internacional de Agricultura Tropical (CIAT), Apartado Aereo 67-13, Cali, Colombia. Joan Crabtree, Tropical Products Institute, 127 Clerkenwell Road, London, England ECIR 5DB. Bengt Dahlberg, Alfa-Laval AB, Postfack S-147 OO, Tumba, Sweden. Alphonso Diaz, Centro Internacional de Agricultura Tropical (CIA T), Apartado Aereo 67-13, Cali, Colombia. Mario Dupont, Grupo de Politica Tecnologica, Acuerdo de Cartagena, Casilla de Correo 3237, Lima, Peru. James Goering, Agricultural Rural Development Division, IBRD, Washington, D.C., USA. Guillermo Gomez, Centro Internacional de Agricultura Tropical (CIA T), Apartado Aereo 67-13, Cali, Colombia. Alexander Grobman, Centro Internacional de Agricultura Tropical (CIA T), ApartadoAereo67-13, Cali, Colombia. Winston Harvey, Department of Crop Sciences, University of West Indies, St. Augustine, Trinidad, West Indies. David Kemp, National Institute of Agricultural Engineering, Wrest Park, Silsoe, Bedford, England MK45 4HS. Dietrich Leihner, Centro Internacional de Agricultura Tropical (CIA T), Apartado Aereo 67-13, Cali, Colombia. John Lynam, Centro Internacional de Agricultura Tropical (CIAT), Apartado Aereo 67-13, Cali, Colombia. Tobias B. de Menezes, Instituto de Tecnologia de Alimentos, Caixa Postal 139, Campinas, Sao Paulo, Brazil. Friedrich Meuser, TUB Institut fur Lebensmitteltechnologie Getreidetechnologie, 1 Berlin 65 Sesstr. 11, West German y. Wilson Milfont Jr, Centro.de Tecnologia Promon, Praia do Flamengo 154 12°, 20000 Rio de Janeiro RJ, Caixa Postal 1798, Brazil. Truman Phillips, Department of Agricultural Economies, University of Guelph, Guelph, Ont., Canada NIG 2WI. Howard H. Richter, Richter Engineering Pty Ltd., 2 Church St., Boonah, Australia Old 4310. Teresa Salazar de Buckle, Instituto de Investigaciones Tecnologicas, Avenida 30 No. 52A-77, Bogota, Colombia. Encik Ayob Sukra, MARDI, Beg Berkunci No. 202, Pejabat Pos Universiti Pertanian Malaysia, Serdang, Selangor, Malaysia. Julio Cesar Toro, Centro Internacional de Agricultura Tropical (CIA T), Apartado Aereo 67-13, Cali, Colombia. Edward J. Weber, Centro Internacional de Investigaciones para el Desarrollo (CIID), Apartado Aereo 53016, Bogota, Colombia. Luis E. Zapata, Instituto de Investigaciones Tecnologicas, Avenida 30 No. 52A-77, Bogota, Colombia. 6 Cassava Processing in Southeast Asia Robert H. Booth 1 and Douglas W. Wholey Tropical Products Institute, London, England, and Malaysian Agricultural Research and Development Institute, Serdang, Selangor, West Malaysia Abstract. The different utilization patterns of cassava in lndonesia, Thailand, West Malaysia, and the Philippines are briefly discussed. Country differences in methods used in the production of chips and pellets are described. The need for further information on ail aspects of chip and pellet quality and quality assessment methods that may be used to influence pricing structures is stressed. The methods used for the extraction of starch and the preparation of cassava pearl and flake are briefly described. One of cassava's major advantages over other carbohydrate/starch-producing crops is that the roots can be put to many uses. In Southeast Asia al one, there are man y different utilization patterns that are influenced by and in turn influence both production and processing patterns. At present, some information is available on cassava exports, but little data exist on the quantities of different products used within the countries. This is particularly true for the amounts used directly as human food, frequently coming from small backyard crops, but it is also true for cassava starch and other products that are locally manufac- tured and marketed (Table 1). In Thailand, cassava is almost entirely utilized as cassava pellets and starch for export. Thailand is the larges! single supplier of cassava products on the world market and is different from other major producing countries, such as Brazil, In- donesia, Zaire, and Nigeria, which ail consume internally more than 90% of their production. In Thailand, cassava does not form an important part of the staple di et of the people. During 1976, Thailand exported approximately 3.5 million t of cassava products valued at approximately U.S. $350 million, making cassava the number two export earner Uust behind rice and superseding both sugar and maize). Of the total volume exported, starch constituted about 7%, and meal, 1Present address: Centra Internacional de la Papa, Lima, Peru. 7 chips, and pellets 93%, 98% of which was in the form of pellets. In terms of value, starch constituted about 11 % of the total earnings. The chips and pellets were largely exported to the EEC, and starch was divided among Japan (35%), Indonesia (29%), the USA (15%), and other countries. In Indonesia, the patterns of utilization differ throughout the country. In Java, a high percentage of the crop is used as a staple food for human consumption in the form of gaplek (sun-dried, peeled root pieces), fresh roots, and traditionally prepared confections. Both starch and animal feed are also produced. In South Sumatra, the situation is similar to that in Thailand in that cassava is primarily exported, although it is also consumed by the settlers. An estimated 180 000 and 140 000 t of pellets were exported to the EEC from Lampung in 1975 and 1976 respectively. In the Philippines, cassava is predominantly used for food and starch production. It has been estimated that 67% is used for human food, 27% for industrial purposes, predominantly starch production, and 6% for animal feed. Furthermore, it is reported that of the total cassava starch, 60% is used for food and 40% for industrial purposes, such as textiles and laundering and as a binder in the plywood and carton industries. Starch is used in the food industry to produce native foods, noodles, sago, ice cream wafers, various bakery products, and also glucose and monosodium glutamate. Starch production in the Philippines is not enough to meet requirements, and cassava starch was imported at approximately 2000 t annually from 1968 to 1972. In Malaysia, two distinct utilization patterns exist. Virtually ail the commercially produced cassava is used for industrial purposes in the production of starch and animal feed, whereas the majority of the backyard crop is used for human food. No reliable statistics are available on the amount produced or consumed. Much of Malaysia's cassava is utilized internally, although considerable quantities of starch and starch-Iike products, su ch as pearl and flake, are exported, primarily to Singapore. In 1976-Tl, it was estimated that about 6000 t of cassava starch were produced each month and 30% was exported. In 1967, it was estimated that the total production of 12 000 t of cassava chips was utilized internally as animal feed and was complemented by locally produced and imported cassava waste from the extraction of starch. Since then, estimates of chip production have varied considerably, ranging as high as 28 000 t for feed millers alone in 1970. No figures are available for the quantities of chips sold directly to consumers for feed. Essentially, no cassava pellets are produced in Malaysia; no chips are exported; and in fact, small quantities of pellets are occasionally imported from Thailand. The large feed millers who use cassava products complain about the Jack of consistent supplies of acceptable quality and quantity. Cassava leaves are also utilized in the region. In Indonesia, the Philippines, and Malaysia, young Jeaves are consumed as a spinach-type green vegetable after boiling. In Thailand, a Japanese factory mechanically dries leaves and green stems collected from plants at harvest time, pelleting the product and exporting it to Japan as a protein source for use in animal feeds. Commercial Processing The methods and equipment use:d in the production of chips and pellets vary in the different countries of the region; for instance, only in parts of Indonesia where chips are still produced as traditional gaplek are the roots individually hand peeled before further proces- sing. In other areas of Indonesia, as in Thailand and Malaysia, whole unwashed roots are fed directly into chipping machines. The amount of soil that passes into the final product is largely determined by soil type and weather conditions during harvesting, wet clay soils tending to adhere to roots. The chipping machines used and, hence, the 8 size and geometry of the chips produced differ greatly within the region. In Indonesia, following hand peeling, the roots are traditionally eut or split longitudinally by hand, frequently into two or four large pieces only. In some of the large Sumatran enterprises, various chipping machines commonly produce fiat transverse or oblique slices about IO mm thick. The chipping machines used in Malaysia consist of a heavy rotating circular steel plate about 12 mm thick and 1 m in diameter to which usually six, but sometimes four or eight, cutting blades are attached. The mild steel blades measure about 40 cm X IO cm X 16 swg (standard wire gauge). One edge is hammered and sharpened into a corrugated cutting edge. Blades of three corrugation sizes are made, but commonly the medium-size ones producing a uniform chip about 6 mm wide and 3-6 mm thick are used. The length of the chips depends on the angle at which roots contact the blades but is frequently around 50-1 OO mm. The blades are removed and sharpened regularly and are replaced at frequent intervals. The chipping wheels are commonly mounted into wooden frames incorporating feed hoppers ·and are driven by petrol, diesel, kerosine, or electric motors. There is thus no such thing as a standard Malaysian chipper; the heavy rotating wheel and mounted blades are, however, common to ail machines. In contrast, the Thai chippers use a thin circular plate that is usually made from the ends of 200-litre (44-gal) oil drums and into which cutting edges are chiseled. These crude cutting plates are usually mounted on a fairly standard machine, frequently equipped with small metal wheels for mobility, and a short elevator that deposits the chipped roots into hand carts. The chips produced are very irregular, lumpy, and often greater than 30 mm thick. The advantages of the Malaysian chipping machines over the Thai machines are that they produce a more uniform product of better geometry and they partially separate the thin brown root skin, which falls to the base of the machines, from the chips. In Indonesia, the hand-cut roots are sun dried by hanging the pieces on fences or spreading them out on woven mats or racks on bare earth or on roofs. In the chipping factories in Thailand, Malaysia, and Indonesia, the common practice is to produce the chips in the early morning and then distribute them over concrete drying yards. Sorne chippers delay spreading until midmorning by which time the drying floors have absorbed some heat from the sun. In Malaysia, the chips are first distributed around the drying yards using small old tractors or cars fitted with wooden boards in bulldozer fashion. The chips are then spread out into a thin layer manually with shovels. In Thailand, the chips are distributed in small hand carts and then spread out manually as in Malaysia. To speed up drying, the chips are usually disturbed every 1-2 hours using simple hand-pushed wooden rakes. At the end of the day or during rainy weather, the chips are heaped into mounds and covered with portable corrugated iron roofs or sheets of tarpauline or polythene. In one drying yard observed in South Sumatra, the concrete was cambered to assist rapid water runoff. Because sun drying is largely dependent on the weather, the duration of drying and thus the quality of the chips varies considerably. Chip size and geometry together with depth and density of chips, i.e., loading rate, also influence drying time. In Malaysia, the loading rate is usually around 377 kg/10 m2 of drying yard (15 tons/ acre), whereas in Thailand it can be regularly as high as 628 kg/10 m 2 (25 t/a). The lighter loads together with the better geometry of the smaller, more regular chips usually mean the chips are dried to a 15% moisture content within 11/2 days during sunny weather. In Thailand, drying to this moisture level regularly takes 3-4 days, but chips are frequently sold after only 1-2 days drying when they still have a high moisture content, commonly in excess of 20%. Similarly, in Indonesia, the tradition ail y produced gaplek has a moisture content of more than 20% even after sun drying for l week. A major factor influencing the final quality of the chips is the quality of the roots being chipped. To produce high quality chips, the roots need to be processed rapidly after harvesting. However, it is common in ail countries in Southeast Asia, particularly during rainy periods, to see very large amounts of already deteriorated roots waiting to be chipped and dried; such roots will never produce high quality chips. The obvious advantage of mechanical drying over sun drying is that it provides a system of continuous processing that is independent of weather conditions. Scattered throughout the region, several mechanized chipping, drying, and pelleting plants have been installed. The majority use oil-fired rotary drum driers. Although a high quality product is frequently produced, the economics of the various systems available need very careful examination. Pelleting is only practiced in parts of Indonesia and Thailand where the product is primarily for export. It is designed to facilitate bulk handling and to reduce the shipping costs. Two types of pelleting units are in use: highly automated units imported usually from German y, Switzerland, or USA and native plants that are produced in Thailand. The diameter of the pellets produced is 8-10 mm. In Indonesia, the dried chips and gaplek are first hammer milled, whereas in Thailand they are smaller and commonly fed directly into the presses. The native pellet plants do not usually incorporate material precondition- ers; thus the chips are fed directly into the pelleting dies or are sometimes simply sprayed with a little water. The recommended moisture content in pelleted cassa vais 16-18%; frequently, however, chips with a much higher moisture content are used. Native plants commonly do not have or do not operate either a pellet cooler or a pellet screen and simply bag ail the material directly from the presses. This contributes to the generally poor quality of native pellets, although brand pellets are frequently equally poor because conditioners, coolers, and screens are often Table l. Production and utilization of cassava in Southeast Asia. Indonesia Thailand W. Malaysia Philippines Production a Area (millions of ha) l.50 0.43 0.01 0.09 Yield (t/ha) 8.61 14.82 21.63 5.39 Production (millions of t) 12.92 6.36 0.26 0.48 Utilization b Human food * * * Starch (internai and export) * * * * Animal feed: internai * export * * 3 Source: FAO Yearbook 1975. "Key: *positive, - negative or only small amounts. 9 Fig. /. ln Thailand, the bulk of cassavafor export is pelleted i11 local mi lis. The pellets produced often are adulterated and have a high 111oist11re co111e111. by-passed to effect economies. In Thailand, in particular, it is common to find extraneous materials, such as sand, corncobs, and cassava waste, being introduced into the presses. This adversely affects the quality of the pellets and reduces the life of the machinery. Thus, in general, very poor quality pellets of friable consistency are produced. Although official stan- dards exist, they are frequently not met, and complaints concerning quality and physical condi- tion of exported pellets are common (Fig. 1). Although many of the technical factors affect- ing pellet quality are well known and understood by the industry, there remains little or no incentive to improve product quality. As long as pellet producers and chippers are paid poorly regardless of quality, they will generally produce a poor product to gain in weight and throughput and thus reduce production costs . Large differences exist in the organization of the industries in the region. ln Indonesia, a high proportion of the dried material for pelleting is produced in the form of gaplek by small farmers and is in the farmers' house until it is collected by buying agents who quickly send it to the pelleting godowns. The godow11s are large steel and brick buildings where, owing to the seasonality of cassava production in parts of Indonesia, the gaplek may be stored for many months before processing. The long storage together with the high moisture content of the gaplek encourages 10 mou Id attack and insect infestation, both of which are common. In Malaysia and Thailand, the dried chips are bagged in jute sacks containing about 70-80 kg and then stored in sheds. Malaysian chips are rarely kept long before despatch whereas Thailand's chips are sent to the pellet producers where they are stored, frequently for long periods, either in sacks or in bulk. During storage, mould growth and insect infestation are common. Most pellets are bagged and transported to the harbour where they are kept in large godowns or are stored in special bulk silos to await shipment. In Thailand, therefore, the industry is fairly frag- mented and intermediaries are involved at various stages. In Malaysia: the industry tends to be more integrated, and an increasing number of factories have both chip- and starch-processing facilities, enabling them to switch production depending on market prices and weather conditions. Research and development programs exist in several countries, and much technical information on improved chipping, drying, and pelleting methods is becoming available. One interesting development is the cutting of roots into cubes rather than chips. Cubes, once dried, can be readily bulk handled and so the process of pelleting is avoided and thus the scope for product adulteration is reduced. However, the likelihood of much technology being applied in the industry as a whole is slight under the present marketing and pricing structures. More research data on the importance of ail aspects of product quality and quality assessment are required so that appropriate price structures incorporating quality incentives may be soundly drawn up. Starch Production In ail countries in the region, starch is commercially produced from cassava roots. In many parts, the extracted starch is commonly referred to as "flour"; however, it is considered desirable that the term "flour" be restricted to ground or milled dried products and that the term '' starch'' be used for the extracted product. The basic process of starch extraction involves root washing; root crushing/rasping/disintegrat- ing; starch extraction; starch washing/refining; starch dewatering; and starch drying (for more detailed discussions, see Salazar de Buckle p. 26 and Dahlberg p. 33). Generally speaking, two processing methods together with various combi- nations of these are used throughout the region. One method employs the traditional sedimentation technique and the other uses more modern machinery, such as centrifugai separators, refin- ers, and flash driers. In the region, the starch extraction industry has been changing rapidly over recent years and many factories are now using modern equipment and methods. Using conven- tional methods, a total processing time of about 5 days is required, much of this time being absorbed in the repeated washing and resettling of the starch. Using modern equipment, the total proces- sing time is reduced to 1 day or even Jess. The mechanization of starch production results in not only shorter processing time and a higher throughput but also a higher quality product. Due to the reduced processing time, there is a much lower degree of fermentation and the starch, which is centrifugally extracted, has a higher viscosity, an important consideration for the textile market. Also, substantially higher extrac- tion rates are obtained in modern plants. For starch extraction plants to run successfully, very careful management is required. Continuous availability of freshly harvested roots is, of course, a major prerequisite, and for the produc- tion of top quality starch, the roots should be processed within 24 hours of harvesting. Delays, li beyond this, result in the lowering of product quality, and roots aider than 3 days pro duce a very inferior product. Unfortunately, it is only too common to see already deteriorated cassava roots being utilized in a modern extraction plant capable of producing top quality starch. A further requirement in starch production is a continuous and reliable water supply. It is estimated that the total quantity of water required to process a ton of roots is 14 000-18 000 litres using conventional methods and about 8000 litres using modern equipment. For certain phases of the process, especially the purification of the starch, highly purified water is required. Dissolved impurities contaminate the product and those high in iron content discolour the starch. Treatment of water with sulfur dioxide, a sterilizing and bleaching agent, is practiced in many of the modern plants. lt has been observed that general sanitation conditions in many of the factories, particularly those using sedimentation techniques, are unsatisfactory. In factories using traditional sedimentation techniques, flake and pearl are sometimes pro- duced by additional processing of the moist starch. Pearl is made by placing partially dried, or a mixture of wet and dry starch, into open, slightly inclined cylindrical rotating drums. During rota- tion, the starch grains adhere to form small beads, the sizes of which are influenced by the speed and duration of rotation. The raw pearl is then size graded, placed in iron pans, set in fire bricks, and heated from below by a wood fire. The pans are slightly greased and are rotated. The baking takes about 3-5 minutes at a temperature of about 65-75 °C, which causes the starch to gel. The baked product is again size screened into different grades of pearl (saga) and finally dried for 12-24 hours on wood-fired, starch-drying yards. Flakes are irregular lumps of semigelled starch prepared in a similar manner to pearl except that the moist starch is not formed into beads. The waste material from starch plants is used in various ways. In Malaysia, it is sold to local farmers either in the wet state or following sun drying. In Thailand, the refuse is commonly sun dried and then sold to cassava-pelleting factories where it is incorporated into cassava pellets for export. Cassava Processing for Animal Feed 1 Rupert Best Grupo de Politica Tecnologica, Acuerdo de Cartegena, Lima, Peru Abstract. An inclined tray-drying system for cassava chips was developed at CIAT and tested against traditional concrete floor drying in five locations throughout Colombia with varying climatic conditions. The results obtained show that tray drying can double the output per unit area of drying surface compared with concrete drying. In areas where it can be guaranteed not to rain overnight a greater improvement in performance is achieved if drying is started between 1400 and 1700 hours. The loss of moisture at night is greatest where there are high windspeeds. The cost of materials for constructing the trays and their supports is lower than for laying an equivalent area of concrete, but the cost of maintenance and the life of the trays has not yet been determined. The possibility of combining natural drying with solar or artificial drying is discussed with a view to improving the product and to reducing the dependence on weather conditions. A number of options are already available and could be evaluated under practical conditions. The enormous potential for using cassava as a feed for ail types of livestock has recently been recognized (Coursey and Halliday 1974), and a large amount of research has been devoted to defining the optimum levels of dry cassava in animal diets and to modifying the plant's chemical and physical properties that restrict its use (Neste! and Graham 1977). At present, countries within the European Economie Community (EEC), where the high price of cereals has stimulated the search for alternatives, are the principal importers of cas- sava. ln future, other industrialized nations, such as Japan, Canada. the United States, and Eastern Europe, may find it economic to use cassava as a feed ingredient (Phillips l 974a), and the produc- ing countries themselves will likely use more 'In the text of this paper ail moisture contents are given on a wet basis; on some graphs they are given on a dry basis to emphasize the difference in water content of cassava when comparing drying methods. The moisture content on a wet basis (mcwb) is the grams of water in a 100-g fresh sample: %mcwb=Mw/Mw-Md X 100, where Mw=weight of water in sample and Md=weight of dry matter. Fresh cassava has a moisture content of 60-70%, wet basis, which is equivalent to 150-233%, dry basis (%mcdb = Mw/Md x 100). For safe storage, the moisture must be reduced to 14%, wet basis, or 16% dry basis. 12 cassava for feed as the demand for hvestock products increases. Thailand and Indonesia are the world's largest exporters of dried cassava, largely in the form of pellets. These countries, together with Malaysia, which produces dry cassa va for internai use, have well-established industries that clean. chip, sun dry. and pellet the roots. ln other countries of Asia, Africa, and Latin America, where cassava forms an important part of the staple d1et, it is grown principally by small farmers for family consumption or for sale in the local market. It is virtually ne ver dried for animal feed, although the small or large roots that are unsuitable for human consumption are often fed fresh to the household pig. Currently, the yields are often poor, although improved varieties of cassava and better agricultural practices can markedly increase yields (Centra Internacional de Agricultura Tropical 1975; 1976). Low yields and small agricultural markehng units make it economically unfeasible for the compound feed industry to substitute cassava for other sources of energy, such as maize and rice bran. Capital-intensive processing plants require a constant supply of high-quality raw material. Thus, a processing technology that suits small farmers or small-to-medium industries is needed in cassava-producing countries. In this respect, much can be gained from studying the established industries of Southeast Asia. Natural Drying in Southeast Asia The majority of the cassava processed for animal feed in Southeast Asia is sun dried. The Malaysian and Thai industries are well developed with some processors handling up to 25 t/day of fresh mots. In Indonesia, drying is carried out on a smaller scale by individual farmers. The techniques used in each country are basically the same, differing only in the level of mechanization (Manurung 1974) . A high quality product depends on good management at each stage of processing. Careful harvesting reduces damage to the roots and thus cuts down on deterioration before drying. Al- though it is unnecessary to peel the roots (as is done in Indonesia), the removal of clinging mud by washing improves both the visual and nutri- tional quality of the final product. The roots may be cleaned manually in concrete tanks or mechan- ically in rotary washers depending on the quantity to be processed. Slicing or cutting is then carried out to reduce the size of the mots , which are spread either on concrete floors (Malaysia and Thailand) or on bamboo mats (lndonesia) to dry; the chips are turned from time to time to ensure uniform drying within 2- 3 days. For the export market, it has become the custom to pellet the dry cassava. This eliminates dust and gives a uniform product with improved handling properties and an increase in weight-to-volume ratio of 25-40%, which substantially reduces the freight cost . The greater care taken by Indonesian farmers results in a higher quality product than that produced in Thailand. Thai pellets contain high levels of silica and fibre caused by the drying of unwashed roots together with the adulteration of the chips with fibrous material and sand in the pelleting process; they also suffer from high microbial contamination caused by poor chipping and inefficient drying. The Asian Institute of Technology (AIT) is investigating better chipping Fig. J. This is the final arrangemellt of the supporti11g frames showing u11its of four travs with gaps left bet1\'ee11 them to enable stacking at night or before rain. The horizontal trays, one on top of the other, are covered b.v corrugated iron or canvas, the pile being raised off the ground on two bamboo posts. The method of supporting the lower edge of the trays on the frame is a/so shown with a one-third section of the /01\'er bamhoo rail eut away . 13 and drying methods, but existing price differences between good and poor quality products (Muller 1977) offer little incentive for improving prac- tices. Tray-Drying System Investigations by Roa (1974) at CIAT showed that cassava dries more rapidly when the circula- tion of air is improved by placing the chips in mesh trays raised off the ground. To take full advantage of the drying power of the wind, the trays should be held vertically. However, in a practical system, the trays are more conveniently held at an angle that does not require expensive innovations to keep the chips from sliding to the bottom of the tray (Fig. 1 ). Experiments indicate that wooden-framed trays, 0.90 m X 1.70 m X 50 mm, can be propped at an angle 25-30° (300 mm off the ground) without disturbing the chips, although in high winds a smaller angle may be required. The trays, made of plastic mosquito screen and chicken netting, can hold 30 kg of fresh chips. Trials were carried out to compare concrete and tray drying at CIAT and in four other locations in Colombia, selected for their wide variations in climatic conditions. The results obtained are discussed in this paper with reference to the parameters that affect the drying time. The quality of sun-dried cassava depends to a great extent on the drying time - the shorter the process, the lower the Joss of carbohydrates by fermentation and the lower the level of microbial and dust contamination. The parameters that contrai the drying time are the geometry (shape and size) of the cassava chips; the chip loading on the drying surface; the climatic conditions of air temperature and humidity, windspeed, and solar radiation; and the fresh moisture content of the cassava. Under natural drying conditions, it is only possible to control the chip geometry and loading, whereas using artificial heat driers, the air temperature and velocity may be optimized to reduce the drying time and provide better quality. Chip Shape and Size Moisture is removed from cassava by diffusion from within the material and evaporation at the surface. Hence, the rate of drying depends on the chips' surface area and on the rate of removal of saturated air from the surface. This means that the drying time may be shortened by cutting the cassava roots into chips that are sufficiently th in to 14 maximize surface area but retain their structure uniformity to allow the free circulation of air around them. According to Roa ( 1974), the optimum natural drying characteristics are ob- tained by cassava chips in the form of neat, uniform, and firm rectangular bars of dimensions 8 X 8 X 50 mm. In practice, this geometry is hard to achieve other than by a hand-operated chipper. At AIT, chips produced by a Malaysian cutting machine have been compared with chips of regular dimensions and similar size and found to give satisfactory results. Mal aysian cutting machines (Fig. 2) reduce the cassava roots to chips approximately 4-8 mm thick and I0-80 mm long, which are smaller and more regular in size than the chips produced by the equivalent Thai machines and consequently dry more rapidly. The corrugated blades, which in Malaysia are hand forged by blacksmiths, could be difficult to make in some countries. A similar blade can be pressed out with a tool developed by the industrial development department of the Tropical Products Institute, London (Best 1978). This type of blade was used successfully for the trials in Colombia. Chip Loading The number of chips spread out per unit area also affects drying time. In Th ail and, cassa va is spread on the concrete drying surface at a density of 6.1 kg/m 2 (IO t/rai), drying in 3 sunny days. In Malaysia, chips are spread at 3.7 kg/m 2 (250 pikuls/acre) and dry within l. 5 days (Manurung 1974). The first experimental trials to be carried out in trays were those of Lavigne ( 1966) in Madagas- car. Using chips 6-8 mm thick and 80 mm long, spread at I0-15 kg/m 2 on horizontal split bamboo trays raised 40 cm above the ground, Lavigne determined that 70 hours of sun were necessary to dry the product. The colour and odour were most acceptable when the 70 hours were distributed over fewer days. Roa ( 1974) compared concrete floor drying with horizontal and vertical mesh tray drying. Making use of a computer mode! to interpret his results, he predicted that, to complete drying in 3 days, the following chip densities are permissible: 5-13 kg/m 2 on concrete, 20-30 kg/m 2 for horizontal trays, and 30-40 kg/m 2 for vertically held trays. The advantage of drying in mesh trays has also been illustrated at AIT, where a possible 73% increase in chip production over traditional Thai methods was estimated. The improved circulation of air obtained in inclined trays permits higher chip-loading rates than on concrete. The optimum thickness of chips Fig. 2 . The chipping machine shown here is a modijïed version of a design developed by the Farm Mechanisation Branch of the Department of Agriculture , Serdang, Malaysia. lt is drive11 br a 3 BHP petrol motor with a throughput of approximately I t /h and 11wv be constrncted in 1\'0rkshops with ll'eldi11g and oxyacetylene cutting facilities . on the tray depends on the windspeed n 12345678910 noon Time of day 11 12 13 14 15 16 Drying hour~ Fig. 4. In this typical drying curve. water Joss is rapid ta begin with. reaching a maximum at 'nidday and then decreasing. At 1800 hours the moisture content of the cassava is sufficient/y /ow (Jess than 20%)for water ta be absorbedfrom the air overnight. On the fol/owing day. water Joss is very slow. requiring 5 hours ta complete the drying. following day was at its peak. Night drying at CIAT used a total of only 7 daylight hours ( 1 hour the lst day and 6 the next), whereas normal drying requires 15 hours of sunlight. U nfortunately, weather conditions are not so favourable everywhere, and the trials at other locations produced Jess perfect results (Table 3). The 17 Cassa va (kg) Water removcd from cassava Water contained in cassava Casrnva dry matter mid night 60 55 50 45 Cassava 40 moisture • ~2 content(%) l'o Fig. 5. Tray-drying curvefrom 1700 ta 1700. findings were that the number of daylight drying hours was at a minimum when cassava was chipped between 1400 and 1700 hours. Table 4 gives the Joss of water during the night with the respective climatic conditions, confirming that the windspeed is the controlling factor during the initial stages of drying. Night drying is advan- tageous if it can be guaranteed not to rain overnight, an assumption that can only be made at certain ti mes of the year. A significant reduction in the time required for drying on concrete can be obtained by painting or pigmenting the concrete surface black to increase the absorption of solar radiation (Table 1). Thanh et al. (1976) reported temperatures of up to 6 °C higher on black concrete. The increase in temperature reduces the relative humidity of the air around the chips, a factor that is of particular importance in the later stages of drying. There is a danger that the white cassava dust left behind on the drying floor will reduce the effect of the black surface; during CIAT trials it was necessary to wash the floor regularly. lt will be interesting to learn if this has been a problem in the further work carried out by AIT under pilot-scale operation. Cassava Moisture Content The moisture content of fresh cassava, which varies according to the variety, age at harvesting, the soil conditions, and the rainfall, normally ranges between 60 and 70%. This variation represents a 30% difference in quantity of fresh cassava needed to produce 1 t of dry chips (2.4 t and 3.2 t respectively). Therefore, the selection of a high dry-malter variety increases the dry yield and reduces the labour requirement per tonne, an important consideration in a labour-intensive process. Although, in theory, the lower-moisture var- ieties should dry more quickly than others, in practice, the difference is minimal because the extra water is removed rapidly in the initial stages (Fig. 6). In some ways, this illustrates the inefficiency of natural drying in that only a very small proportion of the available energy is used for drying. If the same cassava were to be dried artificially, bath the drying time and cost would be greater for the cassava with a higher moisture content. The Brazilian heat-drying process of Maquina D' Andrea (Vitti 1966) incorporates a dewatering operation before drying. The chips are hydrauli- Table 3. Daylight drying hours for cassa va chipped at different times of the day. Average climatic conditions over trial period Temp Humidity Location (oC) (%) Sevilla 31 67 Espinat 29 60 Palmira 26 68 Caicedonia 26 69 El Darién 23 72 "Time of starting trial. bMoisture content at that time. Solar Windspeed radiation (m/s) (cal/cm2/s) l.14 0.74 0.66 0.66 l.26 0.61 0.90 0.72 l.73 0.70 Hours required to dry to 14% moisture content (wet basis) Concrete Inclined trays (5 kg/m2) (10 kg/m2) 08ooa 08ooa l lOOa l400a l700a 9 14 10 9 ll ll 13 lO 9 6 14 12 9 6 8 14 14 12 ll 15 (l6%b) 13 13 12 12 l l (l5%b) Table 4. Moisture loss at night. Average climatic conditions between % Loss of moisture between l 700 and 0800 l 700 and 08ooa Relative Cassa va chipped at Temp humidity Windspeed Location (oC) (%) (m/s) 0800 l lOO 1400 1700 Se villa 27 84 0.15 -l 0 8 10 Espinat 27 71 0.35 4 ll 29 35 Palmira 22 79 0.87 -2 2 18 49 Caicedonia 20 87 0.45 -2 2 7 9 El Darién 19 87 0.30 -5 l 3 5 aNegative value denotes absorption of water. 18 cally pressed to remove 25-30% of the water with the result that the drying time and fuel consump- tion are reduced. An attempt was made in Colombia to adopt this practice using a manually operated batch press with a capacity of 70 kg/batch or 210 kg/h. Extraction of water was satisfactory at about 30% but nothing was gained on subsequent natural drying (Fig. 7). Approxi- mately 6% dry malter (predominantly starch) was removed with the water and, unless recovered through sedimentation, represented a Joss of feeding value in the final product. Furthermore, the extra handling required to press the chips increased the labour requirements and overall drying cost. 320 300 2BO 260 240 220 200 % Moisture lBO content (Dry basis) 160 140 120 100 BO 60 40 20 BOO 10 OO 12 OO 1400 Drying Systems: the Choice Farmers traditionally use the most economic drying method available to them, whether it be DRYING OF HIGH- AND LOW-MOISTURE CONTENT CASSAVA IN INCLINED TRAYS AT 10 Kg/m2 -e- M Col 1684 Initial Mc( DB) 318 t2 -D M Col 22 Initial Mc(DB) 179 t1 1600 1800 8 OO 10 DO 12 OO 14 OO Ti me of day 75 70 65 60 55 50 40 30 20 10 0 %Moisture content (Wei basis) Fig. 6. Drying ofhigh- and low-moisture content cassava in inclined trays loaded at JO kg/m 2• % Moislure content (Dry basis) 200 180 160 140 120 100 BO 60 40 20 • Unpressed chips o Pressed chips 8 OO 10 OO 12 OO 14 OO 16 OO 18 OO 8 OO 10 OO 12 OO 14 OO Time of day 65 % Moisture content (Wetbasis) 60 55 50 40 30 20 10 0 Fig. 7. Drying ofpressed and unpressed cassava chips in inclined trays loaded at JO kg/m 2• 19 spreading the crop in the front yard, on the rooftop, or on the edge of the nearest paved road. The sophistication of the method usually corres- ponds to the quantity and value of the product. Thus, coffee driers have sliding roofs to protect the crop from rain, and cassava starch is dried in wooden trays raised off the ground to prevent contamination by dust and dirt. The question is whether the value of dried cassava for animal feed justifies the use of an improved technology, such as inclined tray drying. In Thailand and on farms that have concrete drying patios, the capital has already been invested in the system, and there would be little sense in adopting a new one. However, when starting from scratch, tray drying has advantages that should not be overlooked: the drying area is eut in half; labour input is reduced because the chips seldom need turning and do not have to be respread each day; and the final product contains a lower proportion of fines and dust owing to reduced handling. Any cost comparison of the two systems is location specific, depending on the availability and price of materials. At CIAT, it appeared that the capital cost per unit throughput could be 30% Jess for tray drying (Best 1978). Large-scale operations, such as the Thai industries would have to be better organized for tray drying than they are at present. The trays must be loaded with a certain amount of care to ensure uniform drying and must be carried to the drying racks by trolley, cart, etc. The feasibility of the system needs to be tested under real conditions, particularly to evaluate its two major disadvantages - the level of tray maintenance and their use fui life. Combining Drying Systems It appears that the greatest problem in natural drying, whether on concrete or in trays, lies in the reduction of the moisture content from around 35% to a safe storage value below 14%. Although this range represents only 25% of the total water content of the cassava, its removal can occupy up to half the drying time. This problem could be overcome by combining natural drying with the use of either solar-heated air driers or artificial driers to reduce the dependence on the weather and give greater operating flexibility. There are a variety of solar crop drier designs available from the Brace Research Institute; McGill University, Canada, that might be adapted for partially dry cassava. These designs need to be built and tested under farm conditions to establish their technical and economic feasibility. 20 Within ex1stmg constraints, the most suitable artificial driers are through-circulation batch driers, commonly used on farms for drying grain. They usually have three components - drying bins, which are of simple construction from local materials; fans; and auxiliary heaters, both of which are available in most countries. The running costs of the driers can be appreciably reduced by employing fans that pick up the waste heat from the engine. Depending on the quantity of cassava to be handled, there may be no further source of heat necessary. De Padua (1976) gives a good description of through-circulation driers, explaining the fuel options available (oil, gas, or solid fuel), types of burner, and choice of fan. Under certain circumstances it might be worth- while considering the use of the cassava stems as a source of solid fuel. A number of laboratory studies have been carried out to determine the optimum parameters - bed depth, air temperature, and velocity - for through-circulation driers (Chirife and Cachero 1970; Chirife 1971; Webb and Gill 1974). This work was done using uniform chips of fresh cassava and should be substantiated on a pilot scale using machine-eut roots. In this respect, the available cutting machines may require further improvement to produce more uniform chips and reduce the pressure drop across the bed. For bed depths up to 120 mm, the drying time is not increased at speeds greater than 5000 kg/h/m 2 , and scorching of the chips occurs above 84 °C (Chirife and Cachero 1970). The optimum condi- tions for partially dried cassava are likely to be different, with the possibility of using greater bed depths and a decreased air-flow rate (Webb and Gill 1974). Lister (Lister Farm Equipment Limited, Durs le y, Gloucestershire GL 11 4HS), manufac- turers of through-circulation farm drying equip- ment, claim that thëir moisture extraction unit is suitable for drying cassava. Their double-bin, reversible-flow system uses drying air to a maximum by passing it first through one bin containing partially dry cassava and then through another that is charged with fresh cassava. The basic unit gives outputs of 2-7 .5 t/day, depending on the number of additional heaters used; 2 t/day are obtained using only the engine's heat. This throughput could be substantially increased if a major part of the drying Joad were removed beforehand by natural drying. In conclusion, there exist many options for improving the rudimentary methods of cassava drying that could be put into immediate use and evaluated under practical conditions. Cassava Chipping and Drying in Thailand N. C. Thanh and B. N. Lohani Environmental Engineering Division, Asian /nstitute ofTechnology, Bangkok, Thailand Abstract. Experiments were carried out comparing cassava drying techniques and testing the effects on drying of different chip forms and sizes. Cassava chips of various shapes and sizes (circles. rectangles, cubes, strips, and slices) produced by Thai and Malaysian cutters were investigated, and solar drying methods using plain cernent floors, blacktopped floors, and shelf driers, as well as artificial drying, were compared. It was observed that both blacktopped floors and perforated shelf driers were faster means of drying than regular cernent floors and that drying time was influenced by the shapes and sizes of chips. The data were statistically analyzed and regression equations were developed, providing significant and useful information in the chipping and drying studies of cassava. Cassava, Manihot esculenta Crantz, also called tapioca or manioc, is a starch-producing tropical root crop. It ranks seventh among staple foods in the world and is ubiquitous to Africa and Asia. As a crop, cassava's popularity with farmers is due to several attributes: it is easy to plant, requires little attention, withstands drought and short periods of flood, grows in relatively poor soils, and yields well compared to many other crops. The yield varies from region to region and strain to strain with 2-3 kg of root per plant being common. Improved strains that yield more than 10 kg of root per plant are now available. The optimum yield can be achieved by having 3000- IO 000 plants/ha. Cassava as Food and Feed Cassava is used as a staple food by about 200 million people in the tropics, and large amounts are exported to temperate countries. The United States and the European Economie Community (EEC) are the main importers of cassava products, with the USA being the larges! single market for cassava starch and importing most of it from Thailand. Demand for cassava chips and pellets has increased in recent years in the EEC because of higher grain costs. Cassava is used as a substitute for barley, maize, etc. in Iivestock feed, mainly for dairy cattle, beef cattle, goals, pigs, 21 and chickens. At present, cassava seldom consti- tutes more than !0% of compound feeds. but occasionally up to 40% is used. In the future, cassava has great potential as livestock feed, especially with the rising prices of animal products and quality meat. Future demand will depend on consumptiou of live stock product>. changing composition of reared livestock, chang- ing dependency on compound feed, and increasing livestock numbers. Ali indications are that de- mand for cassava for inclusion in animal feed in the EEC will increase in Belgium, Italy, and Germany more rapidly than in France and the Netherlands. The United Kingdom and Denmark are also potential buyers of cassava feedstuff. Compound feed demand is closely related to livestock product demand and can be estimated from it. The United Kingdom and Denmark, as members of the EEC and as practitioners of a common agricultural policy (CAP), are experienc- ing pressures to increase livestock production due to increased Iivestock prices. Therefore, the compound feed market is expanding substantially; however, the share that cassava products will command has not yet been determined. The prospects for the utilization of cassava products indicate that the animal feed sector is one of the most promising not only in developed countries but also in certain developing countries where people can afford intensi vely produced meat. Taiwan's imports of feed grains have increased from 94 000 t in 1964 to more than 1 million t in 1971. In addition, Japanese buyers, who have previously relied on imported maize for feed, now seem to be active in the cassava market. This suggests new opportunities for export in a number of tropical countries. Cassava Chipping and Drying in Thailand The total world market comprises both domestic consumption and international trade. In Thailand, where production of cassava has increased sharply sin ce 1956, the crop occupies about 2% of the country's planted area and is almost entirely for export. The production of cassa va chips in Thailand is a relatively simple procedure consisting of chipping the roots and then spreading them on large concrete surfaces in the open air. Sun drying usually requires 2-3 days with periodic turning of the chips (until the moisture content reaches 13-15%). Currently, however, drying periods are very short, and the moisture content is rarely reduced below 19%. Sand and waste products, such as cassava fibres, are often added to the chips to minimize the drying time and make the process economically viable. The high moisture content means that the cassava is a favourable medium for the growth of bacteria and mould. It appears, therefore, that there is a need for cost-effective methods for reducing drying time and ensuring acceptable levels of moisture content. Sun drying of cassava chips on plain cernent floors is the most common practice. Discounting weather conditions, the chips' shape and thickness mainly determine drying time, but the colour of the cernent also has some influence. For instance, black surfaces absorb more heat energy and reach higher temperatures than do plain surfaces, thus reducing drying time. Drying Methods: a Study In our study, various shapes and sizes of cassava roots were eut manually and dried on different drying media (Table 1) in an attempt to measure their effects on drying times. Chips mechanically eut using Thai and Malaysian machines were also tested. The Thai cutter was designed to produce irregular, large chips with a capacity of about 9-14 t/hour with 6-8 hp engines. The Malaysian cutter, type Jenis-8, designed by the National Institute for Scientific and Industrial Research (NISIR) consists of two blades producing cassava slices (0.2-0.3 cm thick) at one side and strips approximately 8 X 22 0.65 x 0.65 cm on the other side. With a total capacity of about 3.8 t/hour of chips, it uses a 2 hp engine and has two advantages over the Thai machine: the chips are uniform, and the pulp can be collected separately from the bulk mass of the chips. The manually and mechanically eut chips were sun dried on 2 m x 2 m natural cernent and black concrete floors and on trays. The chips on the floors were turned periodically until the moisture content reached 13-15 % . Turning the chips increases air circulation and aids heat transfer by convection, thus speeding drying. In tray drying, turning is not required if the trays are porous (chicken wire, netting, etc.). A three-tier tray drier was designed and studied as an alternative to concrete ,floor drying. It consisted of four trays that could be adjusted to any of three positions, one horizontal and two tilted at an angle of 20° to the horizontal, either up or down (Fig. 1). The trays on one side were made of bamboo lattice work, the upper one having 2-cm 2 holes and the lower one l .3-cm 2 holes. On the other side, chicken wire was used, and the upper tray had 2-cm 2 holes and the lower one 0.6-cm 2 holes. The lowest level tray was made of plywood and had 1.3 cm clearance from the ground. Trays were designed in such a way that the dried product on the upper levels would fall onto the lower level trays, when unhooked, for subsequent collection. Sun drying is at times unreliable, because it depends on solar radiation. Artificial drying, on the other hand, maintains a consistent environ- ment and may be considered as an alternative. In the present study, artificial drying was carried out on a thermostatically controlled electric hot plate. During drying tests, the moisture content of the chips was determined at regular intervals of 1 or 2 hours. Thermometers were provided to record ambient and contact surface temperatures. Results and Discussion The study was carried out during the hot season (between March and July 1975) when the air temperature varied between 28 and 35 °C. After 24 hours of solar radiation on the cernent floor, the chips contained 15-17% moisture, but the slices (0.1-0.2 cm) contained 14% in 12 hours. An increase in moisture was noted between 2000 and 0800 hours due to the absorption of condensation caused by cooling of the night air. During daylight, the difference between the floor temper- ature and that of the ambient air was about 6-7 C0 • Table I. Shapes and sizes of cassava chips . Shape Diam(D) Circle CRI 4.5 CR 2 4.5 Rectangle RT 1 RT2 RT3 RT4 Cube CU 1 eu, Strip, ST Slice, SL Size (cm) Length (L) 8 8 8 8 1 2 6 Oicken w~e Tm~ 2 cm d10_ Holes - Width(W) Thickness (T) 0.5 1 2.5 0.5 5 0.5 2.5 5 1 1 2 2 0.5 0.5 0.1 - 0.2 b) Fig. 1. A trial load 011 a shelf-trav drier, a); a cross-section, b) . On the black concrete surface, the chips and strips contained 14% moisture after 9 hours of drying. The cubes (1 cm3) also approached 14%. No improvement or deterioration occurred be- tween 1800 and 0800 hours; however, a slight decrease in moisture was noted on the 2nd day of drying. The chips drying on the trays were better looking and more uniformly dried than those drying on concrete floors. The moisture content measured in the slices and strips after 14 hours was 14% or less. A hot plate maintained at 70 °C reduced moisture content to 14% within 4-5 hours for ail the chip sizes. 23 Cost Considerations Although artificial drying is more reliable than sun drying, it requires higher initial investment and may not be feasible for many cassava processors. Concrete drying and tray drying. on the other hand, may mean only limited increases in expenditures - for example, the concrete slabs used by starch manufacturers in Chonburi Pro- vince, Thailand, could be used at limes for chip drying. ln addition, the operating costs for concrete and trays are quite low and, for the latter, may be offset by the land that is freed for other purposes. Chip Form and Size A second investigation was carried out during the rainy season, September-October 1975, this time focusing on sun drying chips in slices and strips produced using a knife, an ice-shaver, and a Malaysian cutter. The residual-moisture content versus time-of-drying was recorded. Tempera- tures varied between 28 and 31 °C. Manually eut strips and slices dried very rapidly on the black concrete floor, and the acceptable level of moisture content ( 12-14%) was achieved in about 10-12 hours. The thin chips also reached 14% moisture content within 12-14 hours on a conventional drying floor. The same remarks apply to the drying performance of strips and slices produced commercially using a Malaysian cutting machine, although the chips were larger than th ose that were manually eut. A 13% moisture content was attained in strips after 14, 13, and 12 hours when dried on a simple cernent floor, the shelf drier, and a black-painted floor, respectively. During the 1 st day of drying, the moisture content in strips was reduced to 30, 26, and 20% respectively. During the night, the moisture content increased by about 2% in most cases and the acceptable level of moisture content (14%) was reached on the 2nd day between 0800 and 1200. Slices required a longer drying time than strips, as previously observed, but the difference was not substantial. The same level of moisture content (13%) in slices was attained after 16, 15, and 13 hours on a plain cernent floor, the shelf drier, and a blacktopped floor, respectively. Statistical Analysis The general trend of the data showed that a polynomial of the form y = a - b1X - b2X2- ... - b0 X0 could predict the behaviour. Computer programs were thus developed to fit a polynomial equation of any order and at the same time to plot the original and the estimated data from the mode!. The computer program was run in IBM 370/145. The regression coefficients were tested for their significance at 95% by making analysis of variance and then performing the F-test. Floor temperature (T r) was highly correlated to the ambient temperature (Ta). A second degree polynomial represented the relationship between ambient and floor temperatures for ail the drying techniques except for shelf drier (middle shelt) for which a third-order polynomial was found rep- resentative. The relations proved to be: Cernent Floor Ta = li. 71 + 0.632 Tr - 0.00256 T 2r Blacktopped Cernent Floor Ta = 19.15 + 0.289 Tr + 0.0007 T21 ShelfDrier Upper Shelf (chicken wire) Ta= -38.9 + 3.56 Tr- 0.042 T2r Middle Shelf (bamboo-net) Ta= -393.95 + 34.85 T1-0.946 T21 + 0.0085 T31 Lower Floor (wooden) Ta= -26.57 + 2.83 Tr- 0.0325 T31 It may be observed from Fig. 2 that the floor temperatures of cernent floor, blacktopped floor, and shelf driers (upper shelt) are respectively 33.5, 35, and 30.2 °C when the ambient tempera- ture is 30 °C. The middle and lower shelf of the shelf drier at the same ambient temperature only reached temperatures of 29. 5 and 30.4 °C, respectively, even though the shelf drier outper- formed the unpainted concrete floor. The superior- ity of the shelf drier is due to the circulation of the ambient air through layers of the chips. Other results from the equations support the experimen- tal findings. The length of time needed to dry the chips is quite important for producers and may be calculated by using regression ·equations. The equations for the chips of various shapes and sizes and for different drying techniques have been developed and may be obtained by writing to the authors. Conclusions Sorne conclusions can be drawn from the study: • Chip drying time can be shortened to a large extent using a blacktopped drying floor or a perforated shelf drier; however, the shelf drier may not be feasible for large-scale use. At present, it appears that the black-floor drying technique is the most promising. • Drying duration ·is greatly influenced by the shapes and sizes of cassava chips. It has been demonstrated that slices and chips produced by a Malaysian cutting machine are excellent in terms of drying efficiency. • This cassava study, which was conducted during the two major seasons of the year, did not indicate any noticeable difference in drying efficiency between the rainy and hot seasons in Thailand. Heat transfer by convection in the rainy season seemed to compensate for heat transfer by conduction in the hot season. 24 • The efficiency of conventional floor drying could be improved by chopping the cassava into thin strips or slices. • Regression equations that were developed from the study show a significant relationship between ambient and floor temperatures for different types of drying media. Also polynomial 45 ! (al 40 (.) 0 .. ~ 35 La... - c Cl) E Cl) (.) 30 25 25 30 35 Ambient, 0 c regression models for cassava drying can be used to relate moisture content with hours of drying. 50 (b (.) 0 45 8 G:: "'C Cl) 40 Q. Q. 0 - .... 0 0 iii 35 ,,. . 30 25 30 35 Ambient, 0 c Note : Not all the experimental points are plotted for Fig.. (a) and (b) Legend: • Experimental Data Fitted Regression Line 45 (cl (.) 0 (.) 0 ..... ~ 40 Ql .c ~ ..... (/) Ql Cl) .c 'i5 (/) :!:! Q. Equation(3l c 35 == ~.. .. Cl) . 9:1 ·= .. 0 0 ..... ..... âl 30 Cl) .c ! .c (/) (/) 25 25 30 35 40 45 50 Ambient, 0 c 45 (dl 40 35 Equation (4l 30 25 25 30 35 40 45 50 Ambient, 0 c (.) 0 ..... Ql .c (/) E ,g 0 CD .. Cl) ·;::: 0 ~ Cl) .c (/) 45 (e Equation(5l 25..._~.._~..._~..._~..._ ....... 25 30 35 40 45 50 Ambient, 0c Fig. 2. Ambient versusfloor temperaturesfor cementfloor, blacktopped cernent, and shelf drier. The authors acknowledge the support of the Interna- tional Development Research Centre. Zahid Mahmud and Golam Mustafa contributed significantly to this study as research associates, and Prof. M. B. Pescod, 25 former chairman of the Environmental Engineering Division, AIT, contributed especially valuable advice and suggestions. Small-Scale Production of Sweet and Sour Starch in Colombia Teresa Salazar de Buckle, Luis Eduardo Zapata M., Olga Sofia Cardenas, and Elizabeth Cabra Instituto de Investigaciones Tecnologicas, Bogota, Colombia Abstract. Small-scale starch extraction in Colombian rural areas is discussed from the technical and economic points of view. A description of the processes used for producing sweet and sour starches is given together with data on possible mechanisms for fermentation in sour-starch production. It is shown that the fermentation step produces surface modifications on the starch granules and molecular breakdown that seem to be essential for use in bread baking. Sweet starch could be upgraded to meet user specifications on ash and moisture content by modifying the washing-peeling and drying steps. The proposed modifications would not affect the profitability of the process and would open new markets for small-scale sweet starch. Sorne recommendations are given. Small-scale cassava starch extraction m rural Colombian areas probably has much in common with that in other countries. lt comprises two processes - sour and sweet - that supply two noncompetitive markets. Sour starch, obtained by fermentation following extraction, is used exclu- sively in the food industry, and sweet starch competes with cornstarch in the textile, paper, and adhesive industries. Sour cassava starch is used in the preparation of pan de yuca, a traditional bread that is made of starch; hard, salted unfermented cheeses; eggs; and water. The functional properties of the two starches differ. When viewed under the microscope using polarized light, the granules of starch are similar in size and shape, although the sour starch granules show a partial Joss of birefringence and a marked tendency to aggregate. Under the scan- ning electron microscope (SEM), the two starches show significant differences. Ali the granules are round or oval in shape, some with truncated concave edges, but the sweet starch granules appear smooth and homogeneous and those of sour, or laboratory acid-treated starches 1 resemble dented balls (Fig. 1). Other properties of the three types of starches (sweet, sour, and acid-treated, Table 1) indicate that fermentation involves more than a surface 1The mechanisms involved in the modification of the starch were studied by acid treatment of sweet starch. attack on the granules. 2 Although the sour and acid-treated starches look similar, there are .substantial differences in the average molecular weight and alkali number (30 000 and 8.2 and 136 000 and 3.5 respectively). Acid treatment produces a viscosity similar to that of the sour starch (Fig. 2) but does not reduce molecular weight sufficiently to be suitable for use in pan de yuca baking (Table 2). lt would appear that the starch molecules break down internally through enzymatic action, probably of microbial origin, produced during fermentation. Quality specifications of starch as currently used by several industrial groups in Colombia are shown in Table 3. They are generally applied to cornstarch, which accounts for a high proportion of the total market, but are also commonly extrapolated to other starches. They include some notable inconsistencies that suggest a Jack of knowledge on the part of starch users - for example: • Regulations for some products insist on the remov al of crude fat or fibre, although it is commercially impossible, and in the case of sausages, makes no sense; 26 • The specifications given for bakery products probably correspond to sour starch, whereas the 2Surface differences between sweet and sour starch can be observed under the SEM, but acid-treated and sour starch appear similar. Table l. Sorne characteristics of sweet, saur, and acid-treated cassava starch. Viscosity' pH (20°C (BU) 10% water Starch Alkali no. a Specific Mol. wtb suspension) (%) (ml/g) vol (g/mol) 90°C 63°C Sweet starch 6.0-6.5 97 l.2 2.0 215.000 l.300 500 Sour starch 3.5-4.0 96-99 8.2 4.2 30.000 560 360 Acid-treatedd 3.5 97 4.8 2.2 136.000 680 200 Acid-treatede 3.6 97 5.1 2.3 550 200 "Reducing end groups determination by the alkali number according to Schoch ( 1967). bPotenciometric method, according to Ceh ( 1976). '5.5% water suspension. ct20 days at 37 °C with a mixture of acetic, butyric, lactic 2: l: 1 acids (pH 3.6). ew days at 37 °C with acetic acid (pH 3.5). Table 2. Functional properties of sweet, sour, and acid-treated starch in pan de yuca making. a Specific Crumb Starch vol. structure Other properties Sour starch 4.2 Loose structure, Thin and crispy crust large alveola Acid-treated b 2.2 Dense structure, Thick crust, characteristic small alveola flavour diminished Acid-treated' 2.3 Dense structure, Thick crust, characteristic small alveola flavour diminished Sweet starch <2.0 Very poor Very light cheese flavour 50°C 800 140 280 300 "Baked product (200 °C) made from sour cassava starch, hard, salted unfermented cheese ( l: l), l egg per pound of starch, and water; no leavening agent is added. Final weight is 22 g. b20 days at 37 °C with a mixture of acetic, butyric, and lactic acids. 'îO days at 37 °C with acetic acid (pH 3.5). Table 3. Quality specifications for starch in Colombia. Characteristic Cardboard Paper Bakery Moisture (% range) 7.0-14.0 l l.0-12.0 14.0 Fat(% maximum) 0.04 absent 0.7 Crude fibre(% maximum) absent Crude protein, Nx6.25 (%maximum) 0.35 0.5 0.6 Ash (%maximum) 0. lO 0.40 0.2 Colour White White Light yellow pH (aqueous suspension) 5.0 7.0 4.2-5.5 Scott viscosity (cold) 80-100 Scott viscosity (hot) 75 Gelatinization temp (0 C) 74 70-75 27 Sausages l l.0-13.0 absent O.l 0.4 0.2 Lightyellow 6.0 90-lOO 80-82 Fig. J. Pho10111icrof?raphs of starch granules: s1\'eet starch. a); sour starch, b); a11d starch tha1 lws bee11 1reated with /actic acid, 10 dm•s, a11d has a pH 3 .6, c ). 1600 CONSTANT TEMP ZONE 90•c - U) 1- z 1400 ::> a: 1200 LLJ c z LLJ 1000 al cr a: BOO al >- 600 1- - U) 400 0 u U) > 200 TIME (min) 0 20 40 60 80 100 Fig. 2. Amvlof?Y<1phs of sweet, a); sour. c); and acid-treated - acetic-b1avric-lactic. 2: I: I 20 davs. pH 3.6. b); <1ceric . 10 da\'s, 37 °C, pH 3 .5 . d) - cassava starches at 5% s11spe11sio11 . other specifications refer exclusively to sweet starch; • Gelatinization tempcratures for sausage use are abnormally high; • Sorne important characteristics, such as speck count and cleanliness. are lacking . No malter how irrational the specitïcations may seem, the starch producers must attempt to comply. At present, cassava starch obtained by small-scale rural processes seldom fulfills user specifications. A typical product may contain 17% moisture, 0.3% crude protein (N X 6.25), 0.4% crude fibre. 0.2% ash. and 0.06% crude fat, its pH ranging between 3.1 and 4 .0 . A detailed look at the steps in starch production brings to light some instances where improve- ments might be introduced. The initial steps (washing. peeling, grating, screening, and settl- 28 ing) are exactly the same for sweet and sour starch . Washing and Grating The roots are received in the factory within 24 hours after harvesting. They have been packed in jute sacks together with some leaves that are said to protect them against mechanical damage during transportation. The raw material is stored for a maximum of 3 days bcfore processing (Fig. 3). During peeling, the workers reject dark mots or cuts of mots as well as any softened or otherwise damaged material. In the large-capacity factories, washing-peeling is mechanized, but generally it is carried out by hand with the help of ordinary knives. Sometimes, it is necessary to follow mechanical washing-peeling by a hand operation. After peeling, the roots are washed, although in many instances they do not become completely clean. The soi! strongly adheres to the inner skin and to the pulp and is doubtless the cause of the high ash content in the finished product. A marked improvement would be possible if the roots were washed before and after peeling. In fact. experi- ments have shown that washing-peeling-washing can eut ash content in half. The peeled roots are fed to a motor-powered grating machine that has a rotating cylinder with sharp protrusions. The roots are pressed against the moving cylinder and reduced to pulp, releasing most of the starch granules. At times, especially using homemade equipment, large portions of roots can go through the machines without being crushed. thus reducing final yield. The grating or rasping machines are, in general, only operated at selected intervals because they have a higher capacity than the equipment for screening. Screening, Settling, and Refining The pulp is fed into a revolving metal cylinder (1 m diameter x 0.80 m heighl) where it is mixed with water. The inner part of the cylinder is equipped ·with buckets that aid in the mixing action and in later discharging the waste pulp. The laierai surface of the cylinder, which has 1-cm openings and a fil ter of cotton cloth inside, acts as a sieve. As the starch granules are set free and suspended in water. they flow through the sieve, leaving the pulp behind. Water is continuously added to the revolving cylinder until a completely clear liquid cornes out. Screening is performed only once. and the screen openings. which approxima le 100-mesh size, are so large that they do not satisfactorily reduce the fibre content. In some less-mechanized processes. a piece of wool cloth is stretched over a container. and when the pulp is fed onto the cloth, an operator mixes it with water by hand. Fig. 3. In this sma/1-scale starchfactory, the roofs are peeled by hand but not washed b~forehand. The ash conte111. therefore, is likely to be high. 29 The starch milk goes to rectangular brick tanks that are covered by glazed tile. The dimensions and number of the tanks vary according to the size of the factory. The starch is allowed to settle in tanks for 3-7 days; then the supernatant water is drawn off to the level of the upper layer of settled material. This layer is called mancha (literally "stain ") and is composed of starch and prote in. It is scraped from the surface of the white starch and discarded. This operation is generally the only refining step conducted, and it is not repeated. Thus, the resulting starch still contains significant quantities of proteinaceous materials. After the mancha has been removed, the product is sweet starch and can be dried directly or allowed to ferment and become sour starch. In the latter process, the starch is transferred to tanks to ferment. In this step, the starch is resuspended in water and left to stand 8-20 days. The settled starch is covered by a thin layer of water, and sometimes a small layer of waste pulp is added. Fermentation Fermentation is produced by several micro- organisms that comprise lactic acid bacteria together with lesser amounts of gram-positive rods (probably butyric acid bacteria), yeast, and fungi. The fermentation lasts for close to 20 days under ambient conditions in the tropical areas (25 °C and 80% relative humidity). Within a few days, the pH drops from 6.5 to 3.5 or even lower and remains stable. Samples taken from three sour starch factories indicated that, after fermentation, lactic acid predominates in the supernatant with acetic - and sometimes butyric - acid also present. After fermentation, the excess water is removed and the product dried. Drying Drying is the same for both sweet and sour starch. The starch is broken into small lumps (1-3 cm) and spread out in thin layers (less than 3 cm) on large open areas for sun drying. It is normally deposited on concrete yards, wooden trays placed on wood supports 1 m high, or on the roof of the factory (some roofs are equipped with sliding lids that can be pulled over the starch in foui weather). Drying generally takes between 24 and 120 hours, during which time dirt contamination is a real problem. The operators move the starch fre- quently to speed up the process, but sometimes 30 during the rainy season, drying is so slow that the starch is spoiled by extended microbial attack. The workers usually judge the dryness of the starch by feeling it. Thus, the moisture content fluctuates and is often too high to meet user specifications. The dry starch is packed in kraft paper bags or in cotton sacks without additional grinding or sieving. Improvement of the quality of the starch 1s obtained with mechanized drying (50 °C, 6 hours), which lowers ash content from 0.20 to 0.14%. Artificial drying is rare, possibly because many people believe that the sour starch cannot be dried at temperatures above ambient. Our studies indicate, however, that drying at 50 °C does not adversely affect the quality of standard pan de yuca. Economies of Starch Production The processing, structure, and uses of sweet and sour starch differ, so it would follow that the economics are also different, as a look at the required investment, production costs, and pro- fitability proves. In calculations presented here, a hypothetical capacity of 500 kg/hour, based on fresh cassava roots, has been assumed, because this capacity corresponds to a large rural starch plant. A typical yield of 20%, 300 days/year, 10 hours/day has also been assumed. The cost/t of sweet starch is approximately U.S. $335.20 and U.S. $340.00 for sour star ch. Capital investment is higher for the production of sour starch (U.S. $30 500) than for the production of sweet starch (U.S. $20 500). Extra equipment (fermentation tanks) and in-process material account for the difference. Machinery constitutes 24.6% of fixed capital in sweet-starch and 45.5% in sour-starch production. Product inventories and credit to customers account for 80-90% of the working capital and for 24-30% of total investment (Fig. 4 and 5). Raw materials constitute 84-85% of the total production costs (U.S. $100 600 for sweet starch and U.S. $102 100 for sour starch), whereas capital charges account for only 1.7-3.2% (Fig. 4a and 5a). The introduction of mechanized drying would increase the fixed capital by 38% and would bring the total capital investment to 24.5%. However, it would increase the total cost of production of sour starch only 3. 9%, be cause the capital charges represent only 3.2% of the total cost. The figures are similar for the sweet-starch operation. RAW MATERIAL PAOOUCTIDN COSTS CAPITAL INVESTMENT Fig. 4. Production of sweet cassava starch (percen- tage distribution of production costs and capital investment). ,, ,. ,,nl rondit1ons Fig. 6. Production of sweet cassava starch (return on investment, Col. $/t). 31 PRODUCTION OOSTS CAPITAL 1 NVESTMENT Fig. 5. Production of sour cassava starch (percentage distribution of production costs and capital investment). 160 140 120 1 OO 80 Ë < ê 60 40 20 16000 17000 18000 19000 20000 21 000 ~<·11111~ pi 1( ni( Fig. 7. Production of sour cassava starch (return on investment, Col. $/t). Selling Price and Profitability Profitability is based on return on investment (Fig. 6 and 7). Operating at full capacity, the manufacturers' return on fixed capital is 59.8% for sweet starch and 133.8% for sour starch. The interrelationships between starch price, fresh cassava roots' cost, and profitability are very important. For example, a selling price of Col. $14 000/t of sweet starch based on Col. $2200/t for fresh roots nets a profit of 40%, whereas at Col. $1900/t for fresh roots, the profit is increased to 95%. A sour starch price of Col. $1700/t and the same cost of raw material means a profit of 107%, going up to 147% for the lower cassava price. The present raw-material costs and selling prices correspond to acceptable levels of profita- bility. Conclusions and Recommendations The raw materials in starch production repre- sent 84-85% of total costs, i.e., the economy of the process is dependent on a constant supply of cassava roots. Thus, efforts to improve agricul- tural yields are necessary if sweet cassava starch is ever to compete with cornstarch for industrial markets. lt will also be important to rationalize the industrial specifications for different cassava starch applications, and it would be convenient to study the possibility of creating agroindustrial complexes in which the agricultural production, the starch processing, and the marketing of the product could be integrated without excluding existing small factories. Studies also need to be oriented toward improving the efficiency of the different opera- tions within cassava starch production, focusing on technology appropriate to the rural processor. The rural cassava starch industry is important enough in tropical areas of Colombia to warrant both technical assistance and financial support. The former should include research into appro- priate designs for solar or conventional starch driers, and the latter should take the form of credit for working capital and for the purchase of additional equipment. 32 Large-Scale Cassava Starch Extraction Processes Bengt Dahlberg Alfa-Laval AB, Tumba, Sweden Abstract. Toda y, efficient systems exist for large-scale cassa va starch production. Based on technology and equipment developed in various starch industries, they make full use of raw materials and produce a minimum of wastewater. Their main problem, which is largely beyond their control, is the suppl y of raw materials, which rarely exceeds 50 t/hour. Starch production today is mainly based on four different raw materials - corn, wheat, potato, and cassava. Ali of the corresponding processes have their own characteristics and problems, although the potato and cassava processes are similar. In one way, however, the cassava process is unique: it is applied in very small rural production units as well as large industrial plants, although the technology is quite different in the two. Big plants in the cassava starch industry are themselves small compared with cornstarch plants, for which a production of 4 t/hour is considered small. In contras!, a cassava starch production of 2 t/hour is already rather big. In the following, I will refer to large-scale cassava plants as those that grind roots at 6 t/hour or more. At this capacity and above, ail the factories use basically the same technology, but small changes can be made to introduce more efficient running procedures and use of the raw materials. Large cassava starch plants must deal effectively with three major problems: ensuring a constant supply of roots; utilizing the by-products; and controlling wastewater. The most important problem is ensuring the supply of roots. Because the roots should be processed within 24-48 hours of harvesting, transportation from the field is a major considera- tion and must be well organized. The factory must work in close cooperation with the farmers or have its own estate, so that planning for growing, transportation, and production can be centralized. At best, the supply of roots to the factory will in most cases not exceed 50 t/hour. The second problem is to devise a satisfactory use for the by-products, which account for about 33 30% of the dry substance and are wasted by most starch producers. The starch is only about 25% of the roots; 65% is water, and the remaining 10% other components. The third major problem is factory effluents, which become a headache sooner or later, independent of location. It is, therefore, advisable to design the process with wastewater contrai in mind. This involves mainly recycling and reusing process water in the system, thereby reducing effluent volumes as well as freshwater require- ments. Process Description The process can best be explained by examining the black diagram in Fig. 1. The fresh roots arrive at the factory in most instances by trucks and should be received in an organized manner. The capacity of the receiving department should be two to three times the average capacity of the factory because roots normally are not delivered more than 8-12 hours every day. Weighing and sampling of the roots are the basis for paying the supplier and can be done in many ways. The roots may need to be dry cleaned before they are weighed because of large amounts of soi! and small rocks. The cleanings should, if possible, be sent back to the fields directly, and the roots should be placed in storage in sufficient quantities to caver that part of the day when deliveries are not made. With a proper design of storage, feeding into the plant is no problem. The roots are then washed and peeled in two steps. The washing is separated from the peeling to utilize the water more efficiently. The water in FRESH ROOTS -----. WEIGHING SOIL GRINDING SLUDGE FERMENTATION DEWATERING DRYING CATTLE FEED STARCH Fig. 1. Cassava starch processing. the washing section picks up soil and dirt and must be continually clarified. At clarification, a sedi- ment, coarse particles, and an effluent carrying solubles and very fine particles are obtained. The effluent is the only wastewater stream from the system and should be taken to a biological treatment plant for reduction of the BOD (biologi- cal oxygen demand). When washed, the roots are peeled, i.e., the outer layer of cork is removed. The peelings are screened off and coarsely ground. The peeled roots are chopped and funneled through a metering device, such as a hopper with a screw conveyer. The level of roots in the hopper, or funnel, indicates when too man y or too few roots are being fed into the system. A simple device can be set up to signal the operator at the root storage to increase or decrease the flow. The next step is disintegration, which frees the starch particles from the fibre. The starch is then extracted, or washed out and separated from the fibre. At disintegration, it is important to separate the starch without creating too many fine fibres, 34 which make extraction more difficult and Jess efficient. Although complete extraction is the ideal, it may not be economical because of the power it consumes. After starch extraction, the pulp is a by-product that can be mixed with the ground peelings and allowed to ferment in a tank to be later dewatered and dried for use as a cattle feed. The chemical reaction in fermentation reduces the toxicity and makes dewatering possible. The extracted starch is concentrated and refined in a separation section, whereafter the soluble components are removed through washing, and the refined product is mechanically dewatered and dried. Although the process is not completely bottled up, it does not let much material go to waste. If the effluent produced at biological waste treatment plants and the soil are discounted, the dry substance recovery is about 94% (Fig. 2). As always in wet processing, a good dry substance recovery is intimately linked to a low freshwater consumption. In the process presented here, Jess than 1 m3 of fresh water is used per ton of roots (Fig. 3). Fresh water is used only in washing so that the starch can be given a very thorough cleaning to remove ail solubles. The water is then circulated into the separation section, where ail the fibres, protein, and most other impurities are removed. From there, it can be used in the extraction, disintegration, peeling, and washing sections. The water that goes to extraction will be purified in the separation process and recirculated, ensuring enough washwater for efficient extraction without large amounts of fresh water. Only small amounts of water are needed in disintegration, and the water used in peeling flows to the washing section and can be regulated to move rapidly enough to be reasonably clean. From the washing section, it flows to the wastewater treatment plant. Plant Description A plant implementing the process concepts discussed above can, of course, be designed in more than one way. The following description is based on well-proven equipment and practical experience. It should also compare favourably with alternatives regarding investments (Fig. 4). When the trucks arrive at the plant, they first pass a weigh bridge. Afterwards, they dump their loads onto a conveyer belt that delivers the roots to a reel for dry cleaning before storing. The soil collected during cleaning is weighed for each FRESH ROOTS (CLEANEDJ 1000 KG 35"/.D.S. • ~ • SLUOGE STARCH CATTLE FEED 120 KG 252 KG 114 KG 10~0.S. Bb"/. O.S. 851.0.s. PROTEIN•35% PROTEIN•D.21. PROTEIN•251. ASH -0.151. CARBOHYDR.•301. PH 4.5-5.5 VISCOSITY Fig. 2. Starch and by-products producedfrom 1000 kg ofroots. truckload and is subtracted from the original weight. The difference is the weight of the cassa va roots, which in the meantime have been moved onto conveyer belts to be deposited in big storage bins. The bins open at the bottom and drop the roots onto another conveyer belt that brings them to the washer. Through this system, labour is kept to a minimum, and the first-in-first-out concept can be strictly applied. The washer is a trough in which the roots are cleaned but not peeled. The water in the washer is continuously recycled over a screen and a hydrocyclone, which take out the solids. As new water is added to the washer, the excess is drawn off and sent to biological treatment. The roots are lifted over a dividing wall to the peeler that agitates them-roughly enough to remove the outer layer. The water in the peeler is sent through a screen, leaving the peelings, which are ground coarsely and sent to the fermentation vesse!. The cleaned and peeled roots then go to a chopper, which breaks them up into pieces of 30-50 mm. The chopped material is collected in a hopper with a screw conveyer that feeds the disintegrators. Although in the past disintegration took two steps, it is now accomplished in a single trip through sawblade rasps. After disintegration, the starch is extracted from the fibres in a six-stage system. The first five 35 stages are static screens and the last stage is a rotating conical screen. The pulp goes to the fermentation vesse!, and is finally dewatered with a belt press - equipment that bas proven itself for this application. The dewatered material is mixed with recycled dry material and moves to a dryer. FRESH liOOTS WASTEWATER DEWATERING FRESH WATER DRYING STAR CH Fig. 3. Wastewater contrai measures for starch production. ]" Fig. 4. Large-scale cassava starch plant. The starch milk from the first screening enters a tank that feeds a centrifugai nozzle separator. It should be noted that this tank is the only one in the process. In contras!, most large factories use a series of tanks through which the starch milk travels. The more tanks there are, the greater the risk of biological degradation of the starch. Operating without tanks has been made possible by pumps that are specifically designed for starch processes. Even without tanks, or rather because of the absence of tanks, the system is very easy to control and operate. A unique automatic control 36 on the centrifugai separator regulates the amount of starch drawn from the tanks, and the level of starch milk within the tank is a measure of the inflow, i.e., whether the feed from disintegration is in step with refining. If not, the screw conveyer to the rasps can be adjusted. The final cleaning of the starch is done by hydrocyclones in four to eight stages, and then the starch is collected and fed through a peeler centrifuge for dewatering before drying. Vacuum filters may be used instead of the centrifuge but are not economical for big plants. Cassava Flours and Starches: Sorne Considerations Friedrich Meuser TUB Insrirur fur Lebens111irre/rech110/ogic Gerreidetechnologic, Berlin, West Gennany Abstract. The main questions in the production of starch and flour from cassava are how to extract the linamarin from the roots, whether or not to ferment the cassava during the processing, and how to dry the product. A few of the possible answers are reviewed in this paper, and the analytic compositions and granular structures of fcrmented and nonfermented cassa va products are discussed. Cassava "flour" is a term that is used inter- changeably with cassava "starch"; for this paper, however, it refers only to cassava meal,farinha de mandioca, or gari. None of these are processed so as to extract the starch. Cassava meal is produced when roots are peeled, chipped, dried, and milled to a fine me al; farinha de mandioca is made by peeling and rasping the cassava roots, then pressing out the water and roasting the moisi mash in copper pans; gari is made by crushing the roots, FARINHA GROSSA BRAS IL which are then left to ferment before drying. Cassava starch is obtained after an extraction process that scparates the starch from the other constituents. After extraction, the starch may be dricd or allowed to ferment to produce almidon agrio or sour starch. This latter process is described in detail in the article by T. de Buckle (p. 26). Fermenting the cassa va starch or flour increases the yield of dry malter by about 20%. ln Fig. J. Samp/es offive cassava products. 37 Table 1. Analytical composition of five cassa va products. Farinha Cassava lngredients gros sa starch (%) (Brazil) (Berlin) Water 9.1 12.0 Starch 87.6 99.3 Sucrase 1. 1 n.d. Glucose 0.2 n.d. Fructose 0.2 n.d. Lactate n.d. n.d. Acetate 0.03 n.d. Protein 1. 9 0.2 Minerais 1. 1 0.2 Dietary fibre 4.6 n.d. HCN(ppm) 2.3 n.d. n.d. = not detectable fermentation, fructose increases rapidly at first (due to hydrolysis of the sucrase), then is converted to lactic acid. The process takes about 3 days after which there is only a small amount of glucose remaining. The formation of lactic and acetic acid lowers the pH and helps preserve the mash. Composition Samples of cassava meal (produced in Ger- many), farinha grossa (produced in Brazil), cassava starch (produced in Germany), and saur starch (produced in Colombia) (Fig. 1) were compared in a limited study to ascertain the differences in fermented and nonfermented cas- sava products. They showed very similar analyti- cal composition (Table !), containing starch and small amounts of lower polymer carbohydrates, minerais, and prote in. The fermented products could be recognized very easily, however, because of their lactate content. Under the electron microscope, greater differences were apparent. For example, many starch granules in the farinha grossa were partially decomposed by amylolytic enzymes and the viscosity of the product was low. Much of the starch was gelatinized. In contrast, the gari had a high viscosity, and, in the sample viewed, the starch granules had been slightly gelatinized by the heat during drying. The cassava meal contained fibres as well as starch, and the residual solubles appeared on the surface of the granules. The saur starch from Colombia had a few fibres and other impurities, but the cassava starch from Germany had none. 38 Cassava Cassava flour starch "Hein" Gari (Colombia) (Germany) (Nigeria) 12.4 8.6 11.7 95.8 81. 1 90.8 n.d. 3.9 0.3 n.d. 1. 7 0.1 n.d. 0.8 0.1 0.4 n.d. n.d. 0.06 0.03 n.d. 0.5 2.8 1. 1 0.4 1. 2 0.8 0.5 5.4 4.0 1.8 436 2.5 Producing Starch and Flour The processes for flour and starch production share two overall problems: how to eliminate linamarin and how to dry the product. The linamarin is the source of hydrocyanic acid (HCN) and must be removed before the product can be consumed. It is commonly removed by extracting the water that contains it, i.e., by mashing and washing the roots. It may also be removed by sun drying, during which the linamarin and linamarase in the roots react and produce HCN. The HCN volatizes and evaporates with the water. Fermen- tation does not remove the linamarin; hence washing is necessary whether the cassava mash is fermented or not. Removing the Water In large-scale operations, decanters may be used to remove the cassava pulp from the fruit water. Composed of a screw-conveyer and a solid bowl centrifuge, they separate the different mgredients in the fruit water through centrifugai force, depositing the components along the walls of the bowl (Fig. 2). The process is continuous - the fruit water and the solids moving counter currently - and is called dewatering. It can easily be combined with washing (removal of linamarin) before drying. Drying is the final step in bath starch and flour production. In the past, it was weather-dependent, with the sun providing the heat. Today, there are several mechanical methods that are suitable for drying starch and flour. They include fluid-bed driers, tray driers, and flash driers. In fluid-bed Fig. 2. One of the 111a11y types of centrifuges availab/c for /arge-scale processi11g . - l Filter 2 W'an • • 3 Gasheatt'r 4 nuid bed dryer 5 Cyclone , ~r.. , 6 Mixer 7 Product recycltnq . - Fig. 3. F/uid-bed drier. 1 tray mov;ng dev1ce 2 tiltable tray 3 tray lifting frame 4 operating stand 5 drying chamber 6 heating chamber 7 main battery. of tieaters 8 intermediate battery of heaters 9 fresh-air inlet 10 exhaust air 2- - 4 5 -6 7 Feed hopper Drymg duct T op·bend classifier Aecirculation duel Cyclone separator Cyclone dus! coltector Fan Heat generator Cold air entry Fig. 5. Flash drier for gritty prod11ct.1'. 10 9 (/) z 0 10 (.) lJJ z :J 0 (/) 0 0 0:: a. ...J 0 I 0 (.) ...J