Establishment of a cassava starch factory

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The following economic study is for the establishment of a modern cassava starch factory with a capacity of 24 tons of dry starch per day. The study includes the estimated required investment and working capital for the establishment and the operation of the factory as well as the estimated operating costs and the expected profitability of the project (see Tables 6-9).

The factory is supposed to be established in a tropical region where all basic industrial requirements such as water, power, transportation facilities and raw materials are available.

The total investment in such a factory is estimated at $736 340 and the working capital is estimated at $142 000 for the operation of the factory for a period of three months. The project is expected to give annual profits of $108970, which is equivalent to 14.8 percent of the estimated invested capital.

TABLE 6. - ESTIMATED TOTAL CAPITAL INVESTMENT FOR THE ESTABLISHMENT OF A CASSAVA STARCH FACTORY (24 TONS PER DAY)

The factory is supposed to be supplied with modern equipment known to have the highest production efficiency. Together with the use of suitable cassava varieties, the industrial yield of starch extraction exceeds 24 percent. In this study, however, a moderate rate of extraction of 23 percent is used.

The cost estimates for equipment and other materials are based on previous studies (e.g.: Grace, Wabby & Eriksen, 1970; Little, 1964) and on quotes from some equipment suppliers. The cost of fresh cassava roots at $9.35 per ton represents the average price in Malaysia in 1969. The estimated wages are based on the highest levels paid in some tropical countries and include all prerequisites, such as annual leave, and medical and social contingencies.

TABLE 7. - ESTIMATED REQUIREMENTS OF LABOUR, SALARIES AND WAGES¹ FOR A CASSAVA STARCH FACTORY (24 TONS PER DAY)

¹Includes fringe benefits.

TABLE 8. - ESTIMATED OPERATING COST AND WORKING CAPITAL FOR THE PRODUCTION OF CASSAVA STARCH (24 TONS PER DAY)

TABLE 9. - ESTIMATED PROFITABILITY OF A CASSAVA STARCH FACTORY (24 TONS PER DAY)

The sales price of cassava starch and refuse is estimated at $78 per ton for starch (f.o.b. price for export) and $35 per ton for refuse, as was reported in 1967 in Thailand. Refuse is extensively used, in the dry or wet state, as animal feed.

OPERATIONAL FIGURES

The factory is designed to operate continuously, three shifts per 24 hours, for 300 days per year. The total capacity is 24 tons per day or 7 200 tons per year of high-grade cassava starch with a moisture content of 10-12 percent.

6. Utilization of cassava products

Cassava in the human diet

Cassava is sometimes classified as a crop for developing countries and for consumption only by rural people, whereas the large crop of cassava grown annually in the tropics is actually consumed in all its forms at nearly all income levels. Originally the cassava tuber was a main food crop only in South America. Nowadays, however, it is grown as a substitute for rice or alternately with rice on extensive acreages in regions where, for centuries, rice has been the sole food crop.

In many tropical countries cassava as the principal source of carbohydrates occupies much the same position in the diet as potatoes in parts of the temperate zones. The cassava tuber is not a balanced food, consisting as it does largely of starch (Table 10); nonetheless, it is the most remunerative of crop plants in the hot climates, yielding perhaps more starch per hectare than any other cultivated crop with a minimum of labour.

During the Second World War, cassava assumed tremendous importance as a famine crop in many parts of the world, especially when rice supplies were cut off. Leaves and lender shoots are used in many tropical areas as a cooked vegetable or in sauces, as they are rich in vitamins and have a high protein count.

MAIN CONSTITUENTS AND NUTRITIONAL VALUE

A comparison of the chemical composition of cassava tubers and some products derived from it (gaplek and tapioca flour) with that of potatoes and rice, as presented in Table 10, may convey an impression of the relative nutritional value of cassava. (It should be borne in mind that only the peeled root is edible.)

As cassava is inferior in protein and fat content to both rice and potatoes, animal protein or products such as soybeans are often used to balance the diet in cassava-consuming lands.

TABLE 10. - NUTRIENTS IN CASSAVA ROOTS COMPARED WITH OTHER FOOD PRODUCTS

Cassava also compares rather unfavourably in vitamin content with other food products, as is shown in Table 11.

Besides starch, the cassava tuber contains some soluble carbohydrates, i.e., glucose and sugar, which can be inverted. These convey a pleasant sweet taste to the tubers of the nonpoisonous strains. The amount in the peeled root is 1-3 percent of total dry matter only, but it rises notably at the age of 16-18 months when the starch content is beginning to decline. The soluble carbohydrate content of the peel is larger - 5-10 percent of the dry matter - and it eventually makes up one fifth of the total carbohydrate content.

TABLE 11. - VITAMINS IN CASSAVA ROOTS COMPARED WITH OTHER FOOD PRODUCTS

These soluble carbohydrates naturally are lost in processing the tubers for starch; they may play an important role, however, in the preparation of fermented food products from cassava.

The nutritive deficiencies of cassava need not be a cause for concern when it is consumed with other supplementary foods. However, the so-called "cassava problem" as related to the "kwashiokor disease" means that persons with low incomes are prone to consume it in excessive quantities because it supplies sufficient calories and gives a feeling of satiety in their diet; therefore, many suffer from a deficiency of protein and/or of vitamins.

Although the cassava tuber may be consumed in the raw state, it usually needs preparing in order to become palatable and digestible and, above all, to eliminate the poisonous prussic acid. This may be accomplished in several ways, thus obtaining various products which are traditional food items in the areas where cassava has long been well known. Some of these have to be consumed immediately; others may be kept for a considerable time and constitute a valuable food reserve.

RAW AND COOKED CASSAVA FOR IMMEDIATE CONSUMPTION

In the raw state the roots of the sweet varieties are used as a forage without being peeled. In the Philippines their suitability in hog feeding has been amply demonstrated in experiments.

The fresh, peeled root of the same varieties is suitable for human consumption, provided it is no more than a few months old, but it is seldom used as such. It cannot be kept for more than a day. The roots of the sweetest varieties are sometimes eaten raw as a between-meals snack or thirst quencher.

With simple cooking the root becomes equivalent to potatoes, though its taste is considered "heavier." Prussic acid in the fresh root is destroyed by slowly cooking the sliced roots, starting with ample cold water so that gradual heating ensures hydrolysis of the toxic principle. If the roots are submitted to fierce heat, thereby destroying enzyme action, a possibility of the retention of bound prussic acid exists, which in the bitter varieties may be dangerous. With the same reservation, steaming and especially frying in oil are recommended, as both these methods produce palatable foods.

In Indonesia, roots are often wrapped in leaves after covering them with a yeast preparation; fermentation for 24 hours suffices to produce a soft and slightly alcoholic side-dish.

Many food dishes using cassava, boiled or baked, as the basic ingredient to which is added meat, fish, soybean cake, shrimps or other protein source are prepared in various countries (e.g.: Krubub, Ketela and fish or prawn crackers in the Far East; Sancochado, Escabeche, Seco de Carnero, Sebiche and Pachananca in South America).

CONSERVED CASSAVA PRODUCTS

Gaplek

The simplest method of conservation consists of drying the sliced root in the sun; in the tropics this takes two or three days. Once dry, gaplek is sufficiently durable; during drying, however, it is particularly liable to mould, making it unsuitable for human consumption. Before the Second World War, the milled product (gaplek meal) was an important export from Indonesia to Europe for animal fodder.

Gaplek meal finds some application in those starch-using industries where the high content of moulds, fibre, and other constituents of the whole root can raise no serious objection, as in textile finishing and the manufacture of alcohol. As it is easy to maintain a large stock of gaplek, there would therefore be obvious advantages in using it as a basic material for the production of pure cassava starch. In Indonesia this use has presented no serious technical difficulties; however, it has never been applied on an important scale.

Farinha and cassava bread (couac)

A somewhat more elaborate treatment of the root than is needed for the production of gaplek leads to conservable food products which seem to be known only in Latin America and play an important role in nutrition there. It is interesting that this mode of preparation is usually combined with the traditional manufacture of crude cassava flour at the domestic level.

The roots, cleaned superficially, are first peeled with a knife and then grated. The most primitive grater, used by South American Indians, consists of a board upon which a number of little flints are embedded in a thin layer of wax. Graters consisting of a wooden board with wooden teeth are also in use. In somewhat more developed areas this work is done with a rotating rasp, usually hand-driven, which does not differ very much from the raspers in rural mills elsewhere.

When a sufficient amount of the rasped material has been collected, it is packed in leaves and pressed under a heavy stone, sometimes with the aid of pole leverage, or in a wooden screw-press. The traditional instrument in

Latin America for this purpose, however, is a basketwork cylinder known as the tipiti, which is specially woven so that it can take both a long and thin as well as a short and bulky form. In the latter form the basket is packed with fresh cassava pulp and hung from the bough of a tree, the "sock" being pulled until it is long and thin. This operation subjects the pulp to considerable pressure, thus extracting the greater part of the possibly poisonous juice.

The pulp obtained may be worked in two ways. In the preparation of farinha it is mixed for better quality with a little pulp which has been left to ferment for three days. The whole is then pounded and rubbed through a sieve, producing a slightly damp meal.

It is then heated, in the open air, in a pan on a flat oven with a top consisting of granite slabs which guarantee even heat without burning. The pulp is turned continuously with a wooden rake during 3 to 4 hours of baking, which produces a granular, only slightly roasted product. If dry, farinha will keep indefinitely. It is an excellent cereal, usually eaten like rice in combination with other foods, especially meat and gravy, but it is also very useful as an emergency ration for travellers. It is known as farinha de mandioca or farinha de mesa.

By heating the pulp more intensively, without stirring, until the mass is slightly brown on one side, it sets into a solid slab. After baking on both sides, the cakes are further dried in the sun, and in this state will keep indefinitely. This cassava bread, or couac, is very hard, but it has an excellent flavour: it is usually eaten after being dipped in gravy.

In rural factories producing farinha or couac, generally only part of the pressed cake of cassava pulp is worked up to produce these products. The rest, in portions, is washed out in a cloth above a wooden bowl, each portion being stirred with successive amounts of water until most of the starch has been extracted. The bowl containing the starch milk is put aside for settling. After some time the water is decanted, and the starch spread in the sun on reed matting. In two days it is dry. The flour obtained, of low to medium grade, is commonly used in Brazil for making cakes.

In Brazil also, the peeled roots are cut into large chunks and dried. The dried product is ground, sifted and the flour, known as farinha de raspa, is mixed with wheat flour in the making of bread, macaroni, crackers, etc.

Gari

A popular food among the low-income groups in west Africa and Nigeria, it is made by fermenting grated cassava tubers, semidextrinizing the mash by heat and finally drying the product to a type of meal. In rural areas, the roots are peeled and grated, and the pulp is put into a large cloth bag and set in the sun to drain and to ferment. When the pulp is sufficiently dry, it is removed from the sack for final drying on a low fire. Fermentation liberates the hydrocyanic acid at low pH and develops the characteristic flavour of gari. It is carried out first by cassava bacteria (Corynebacrerium manihot) that attack the starch with the production of lactic and formic acids, and then by a fungus (Geotricium candida) that acts when the pH has fallen to about 4.2, increasing the acidification and producing the characteristic aroma. Hydrogen cyanide is liberated during fermentation through the spontaneous hydrolysis of the cyanogenic glucoside of cassava at a low pH value. Many attempts are being made in Nigeria to mechanize gari production under hygienic conditions as well as to fortify this low-nutrition food with a protein additive.

Cassava rice (landang)

Similar in properties to these products is landang, or cassava rice, a popular food in the Philippines. Landang retains much of the protein of the cassava root. It is used in the Philippines as a substitute for rice or maize. It may be kept for six months before being attacked by moulds.

This product is prepared by shredding the tubers and pressing the grated mass in a cloth until most of the juice is squeezed out. By whirling the mass in a winnowing basket, pellets are formed, their size determined by the speed of the motion and the moisture content. Pellets of more or less uniform size are isolated by sifting, steamed and then dried in the sun for some days. Alternatively, the tubers are soaked in water in earthenware jars (contact with metal should be avoided) until after five to seven days they begin to soften. Then they are macerated, the fibre is removed by hand and the mass is air dried before being made into pellets in the way just mentioned.

In India the production of a synthetic rice based on cassava has recently been started.

Cassaripo or tucupay

Nowadays the squeezed juice obtained during the preparations mentioned above is mostly thrown away. In South America, however, there is an ancient belief that the juice contains many valuable nutrients.

The method used is to concentrate the juice by means of evaporation, and then add various spices, including chilliest The resulting sauce, which is very similar to a soybean sauce, is called cassaripo or caslup in the West Indies and tucupay in Brazil. If sufficiently concentrated, it may be kept indefinitely. In the cooking process any content of prussic acid is destroyed; in fact, the bitter varieties of cassava give the best cassaripo. In the West Indies, cassaripo (West Indian pepper pot) is used in the conservation of fish or meat, in which case, however, it should be reboiled daily. It is to be regretted that this preparation is out of use now and even totally unknown in countries which are in great need of nutritional condiments.

Pastes

Various forms of heavy cassava pastes are made by pounding the fresh or boiled roots into a very smooth mass which is eaten as a vegetable loaf with an oily sauce. Examples of these products are the fufu of Ghana, the dumbot of Liberia, the atieké of Ivory Coast, the bami of other areas.

New vegetable cheese product

The relative absence in cassava of essential food components, particularly protein, which makes it a cause of malnutrition, has led to the investigation of various methods of adding protein and other nutrients to this basic food. The Tropical Products Institute in London has undertaken studies of yeast culture on cassava and a vegetable cheese is made by the nutritional enrichment of cassava through fermentation. The process consists of fermentation of a cake of extruded cassava dough to which mineral salts are added with a spore inoculum of a selected strain of Rhizopus stolonifer. Crude protein levels have been raised from 0.1 to 4.0 percent, and the vegetable cheese product is acceptable for direct use in cooking.

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