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Cassava (Manihot esculenta Crantz), also known as yuca, manioc, mandioca or tapioca, differs from the other major root crops in that its edible roots are not organs of dormancy and do not appear to have a natural function in the preservation of the plant through the dry season. Thus, the roots are not inherently adapted for survival and once harvested they deteriorate rapidly, developing a vascular discoloration within a few days which renders the roots unpalatable and also unsuitable for subsequent processing (Averre, 1967; Booth, 1976; Montaldo, 1973; Noon and Booth, 1977) .
Traditionally, the problem of storage has usually been overcome by leaving the roots in the ground until needed and once harvested to process immediately into a dry form with a longer storage life (Ingram and Humphries, 1972; Rickard and Coursey, 1981) . The roots can be left in the ground for several months after reaching maturity but a disadvantage of this system is that large areas of land are occupied by a crop which is already mature and is thus unavailable for further use. Also the roots become more fibrous and woody and their starch content and palatability declines (Greenstreet and Lambourne, 1933; Jones, 1959) and in addition, susceptibility to pathogenic losses increases (Doku, 1969) .
One means of storing fresh cassava roots which has been used since ancient times by the Amerindians of Amazonia (Edmondson, 1922), is to bury the harvested roots in pits or trenches, a technique probably derived from the common practice of leaving the cassava unharvested. Similar techniques have also been reported in other areas of the world (Affran, 1968; Irvine, 1969). For a short period cassava roots can be kept fresh by being heaped and watered daily (Affran, 1968) and a coating of paste made from earth or mud is said to preserve the roots for four to six days (Hiranandani and Advani, 1955; H.A.G. Rao, 1951).
Improved storage techniques, not used traditionally and, therefore, not described in this publication, have recently been reviewed by Rickard and Coursey (1981) . Such techniques range from the simple methods of storing the roots in clamps or boxes to the more advanced techniques of cold storage or freezing.
In general, most cassava, if not used immediately after harvest, is processed into a more durable form and a wide variety of food products and beverages are traditionally prepared from the root using a large number of often very complex processes (Lancaster et al., 1982). However, the need to produce a storable product, although clearly important, has not been the only reason for the development of these processes, an additional stimulus having been the need to reduce the toxicity of the root.
Cassava contains two cyanogenic glycosides, linamarin and lotaustralin, which hydrolyse in the presence of the enzyme linamarase, also found in cassava plant tissue, to release hydrogen cyanide (HCN) (Nartey, 1978). Contact between the cyanogenic glycosides and the enzyme occurs only when the tissues are mechanically damaged or there is a loss of physiological integrity, as for example during post-harvest deterioration or wilting of the leaves (Coursey, 1973a). Many of the traditional techniques appear to be designed specifically to bring about the contact between substrate and enzyme by cell rupture, for example, by grating or pounding and elimination of the released HCN is then achieved by volatization or solution in water (Coursey, 1973a).
Studies on the effectiveness of traditional cassava processing techniques in reducing the HCN levels in the roots have been carried out and have been reviewed by Coursey (1973a). This work has shown that the techniques do reduce the total cyanide content of the roots, although the results are often of questionable reliability, due in part to the analytical methods used (Cooke and Coursey, 1981). Recently, however, a new more reliable and sensitive assay for cyanide has been developed which distinguishes between free and bound cyanogenic glycoside (Cooke, 1978) and using this technique it has been shown that while free cyanide is reduced considerably, substantial amounts of bound cyanide may remain in the processed roots (Cooke and Maduagwu, 1978). Using roots with an average initial HCN content of 63 mg HCN/kg, of which 8-12% was free cyanide, the effectiveness of drying, boiling and steeping cassava chips in water was tested. Boiling for 25 minutes removed over 90% of the free cyanide and 55% of the borend. Air drying at 46-50°C removed 82.5% of the free cyanide and 29% of the borend cyanide, with smaller losses in borend cyanide at higher temperatures. Stirring in cold water for short periods was ineffective in reducing cyanide levels but over a period of 18 hours, during which time fermentation set in, a 50% loss of borend cyanide occurred (Cooke and Maduagwu, 1978).
Cases of acute poisoning from ingestion of cassava are occasionally reported (Hanlon, 1981) and high incidences of chronic degenerative diseases, goitre and cretinism have been linked with the consumption of a cassava diet (Oshuntokun 1972; Delange et al., 1982). However, the cases of poisoning are comparatively rare considering the millions of people who regularly consume cassava, suggesting that the traditional detoxification techniques are generally effective (Coursey, 1973a). Both chronic and especially acute cassava poisoning appear generally to be associated with diets that are grossly deficient in sulphur-containing amino acids such as methionine and cysteine which are necessary for the detoxification of cyanide in the body.
Cassava cultivars are frequently referred to as either "sweet" or "bitter", bitterness being associated with higher toxicity, but while this forms a rough guideline there is no exact correlation between HCN content and degree of perceived bitterness (Sinha and Nair, 1968). However, using this terminology it is the "bitter" varieties which are generally subjected to the more complex processes such as are involved in the preparation of farinha or gari in order to reduce the HCN levels, while the sweet varieties are often eaten after more simple preparation methods such as boiling or roasting, or occasionally even raw although they are also processed by more complex methods. The widespread myth that "bitter" varieties have higher dry matter contents and are thus more suitable for processing, has no foundation in fact.
Cassava is believed to have originated as a cultivated plant either in south Mexico and Central America or in northern South America (Rogers, 1963; Renvoize, 1972); it spread in cultivation throughout tropical America before European contact in 1492, and was later introduced to other tropical regions of the world. A great diversity of processing techniques has developed in different regions. Some of the processes are used in all areas either because they are standard methods for preparing starchy food, such as boiling or roasting or because they were introduced with the cassava when it was introduced from South America. Other techniques are unique to particular localities having been developed independently, sometimes based on methods used to prepare indigenous staples (Jones, 1959).
The simplest techniques used to prepare cassava for immediate consumption are boiling, roasting or baking. Peeled roots are boiled whole or sliced and served in a variety of ways. For example, in African countries they are popularly eaten as a vegetable served in a sauce (Affran, 1968; Doku, 1969; Dovlo, 1973; Ekandem, 1961; Favier et al., 1971; Goode, 1974; Whitby, 1972), while in India boiled slices are often incorporated into curries (N.S. Rao, 1951) or grated and mixed with shredded coconut into a product known as puttu (H.A.G. Rao, 1951; Subrahmanyan, 1951). Slices of cassava root are commonly added to stews of other vegetables and meat such as the sancocho popular almost throughout South America (Alba, 1963; Schwerin, 1971). Roasting the roots is less popular with the Amerindians than boiling and generally only resorted to when no cooking utensils are available. Frying is believed not to have been used traditionally but to have been introduced by Europeans (Schwerin, 1971). In contrast, both techniques are widely practiced in Africa both East and West (Alberto, 1958; Doku, 1969; Goode, 1974; Leitao, 1971; Whitby, 1972). Roots are roasted by placing them whole in the ashes of a fire or slices of peeled root are fried in oils of various kinds according to availability and taste. In Vanuatu grated cassava is wrapped in banana leaves and baked in an oven (Massal and Barrau, 1955a).
The more complex technique involving pounding of the cassava roots into a paste is particularly popular on the African continent where it is a very widespread method, also applied to other starchy staples such as cocoyams, yams and plantains (see appropriate sections). The resulting paste from all these crops is generally known in West Africa as fufu, also foofoo, fuifai, foufou, foutou and vou-vou depending on the locality. The term futu or one of its variants is also applied to pastes prepared from cassava starch, flour and grated roots.
Fufu can be prepared by boiling or steaming peeled cassava roots and then pounding them in a wooden pestle and mortar until a homogeneous paste is obtained which is eaten with soups or stews of meat or fish (Affran, 1968; Anasanwo, 1942, Collins, 1911; Ekandem, 1961). An alternative method is to soak the unpeeled roots in water to soften them for pounding, soaking normally being done in running water, i.e. streams, although stagnant water can also be used, for 3 to 4 days, during which time some fermentation may occur. When soft, the roots are removed from the water, peeled and pounded into a paste either to be boiled or steamed and eaten immediately or stored for about a week, often in baskets until needed for cooking or until sold in the market (Ekandem, 1961; Favier et al., 1971; Joseph, 1973; PFL/GAB/001, FAO Technical Report). In Cameroun the paste is made into long stick-like shapes (30-60 cm long and 2-4 cm in diameter) known as batonde-manioc or balls known as chickwangue. These are wrapped in banana or Colocasia leaves and tied firmly for cooking or sale (Favier et al., 1971).
A fermented paste (attieke) popular in the Ivory Coast is prepared by steeping peeled roots in water and then grinding them to a paste which is left for two days in a jute sack under heavy stones to ferment. The paste is removed from the sacks, crumbled by hand and steamed to be consumed with milk or with meat and vegetables (Leloussey, 1970).
The main means of preserving cassava roots for storage is to produce some form of dried product, the end product generally being a flour although the dried roots are often stored in some other form. Many different methods are used for producing flour from cassava around the world, some techniques being used in most cassava growing areas, others being more localized in use.
A technique widely used in Africa to prepare cassava flour is to first prepare a fufu paste as described above and then to dry this either by sun-drying or over a fire. For smokedrying, a method used for example in the forest zones of Cameroun, the paste is made into balls or chickwangue, wrapped in leaves and placed on a screen over the hearth for about 15 days although it can be left longer until needed. After removing the leaves and scraping off the black coating which forms during drying, the dry paste is ground into a flour (Favier et al., 1971; Joseph, 1973). If sun-dried, the paste is simply spread out onto mats for 2-3 days and then ground into a flour (Anasanwo, 1942; Adriaens, 1951; Favier et al., 1981; Joseph, 1973; Whitby, 1972).
In Zambia, cassava roots (either soaked or unsoaked according to taste and the necessity to eliminate cyanide) are mixed with a fermentation starter known as kapapa which consists of partially dried cassava slices that have been allowed to develop a coating of mould. The mixture is left to ferment for 1-6 days, then sun-dried, pounded and sifted into a flour (Whitby, 1972) .
The simplest method used and probably the most widespread certainly in Africa or Asia, for preparing flour from cassava is by sun-drying slices or chips of peeled roots which can then be stored as dried chips and ground into a flour when needed (Alberto, 1958; Anonymous, 1919; Anonymous, 1941; Doku, 1969; Dovlo, 1973; Godfrey-Sam-Aggrey and Bundu, 1979; Tallantire and Goode, 1975; Velcich, 1963) or stored in the form of flour. The sun-dried pieces are known, for example, as gaplek in Indonesia (Anonymous, 1919; Anonymous, 1941) and kokonte in Ghana (Doku, 1969; Dovlo, 1973). Drying generally takes 3-10 days although only 1 or 2 days is sufficient in ideal conditions and once dry, the chips can be stored for 3-6 months, the main problems being attack by moulds predominantly Aspergillus and Penicillium spp., infection generally beginning during the drying stage (Clerk and Caurie, 1968; Rawnsley, 1969) and insects (Ingram and Humphries, 1972 ; Parker et al., 1981; Parker and Booth, 1979) . A method for extending the storage life of chips to up to 12 months and also speeding up the drying process is by parboiling them before drying, a technique often used in India and West Africa (Hiranandani and Advani, 1955; Doku, 1969; Ingram and Humphries, 1972) .
In some areas the roots may be soaked, unpeeled, for about 5 days before drying. For example, in Nigeria a flour known as lafun, an important staple foodstuff amongst the Yoruba of Western Nigeria (Oke, 1965), is prepared in this way and in Angola, bombo or makessu are dried chips prepared from soaked roots which are stored and ground into flour known as fuba (Alberto, 1958).
In East Africa, particularly Uganda and Kenya, the cassava roots are encouraged to develop moulds, before being completely dried ready for storage, by placing the roots either fresh or only partially dried in the dark for several days (Anderson, 1944; Goode, 1974; Tallantire and Goode, 1975).
A variety of methods are used traditionally for storing dried chips. For example, a common method in Zaire is storage in baskets over the hearths where the smoke probably serves to inhibit insect attack (Jones, 1959) while in contrast, in Uganda, storage near a smokey fire is said to make the chips unpalatable and dried chips there are stored in ridded baskets, sealed by plastering with cow dung and standing on stilts (Kerr, 1941).
Dried Cassava chips are sometimes cooked, as for example in India, by boiling or frying (Anonymous, 1952; Subrahmanyan, 1951) but more often they are ground into flour and generally elsewhere flour is the end product. In Africa, the flour is most often mixed with water to form a thick sticky mass or porridge similar to fufu and called by a variety of different names including fufu or one of its variants (Adriaens, 1951; Alberto, 1958; Dovlo, 1973; Ekandem, 1961; Favier et al., 1971; Whitby, 1972). Cassava flour is also made into a sort of porridge in South India (Subrahmanyan, 1951) but more often it is used to make one of the traditional Indian foods such as chappatis (Anonymous, 1952; Hiranandani and Advani, 1955). Cassava flour is sometimes mixed with flours from other crops such as millet and made into a porridge (Tallantire and Goode, 1975) or bread (Ekandem, 1961; Jones, 1959).
Amongst the most important products from Cassava roots are the coarse meals known as gari in West Africa and farinha de mandioca (also called farinha seca, farinha surahy) in Brazil and which are again storable products. The techniques used in the preparation of gari and farinha are very similar, the basic technology having been introduced into West Africa by settlers from Brazil in the early 1800's (Affran, 1968; Jones, 1959). Peeled cassava roots are grated, squeezed or pressed to remove the juice and then sifted and "garified" by roasting on a metal plate. The essential difference between gari and farinha de mandioca lies in the degree of fermentation which occurs before or during the squeezing or pressing stage, gari being left for longer so that a greater degree of fermentation occurs giving it its characteristic sour flavour which distinguishes it from the farinha, and which is preferred by the West African palate.
In South America, once grated, the cassava was traditionally squeezed in a long cylindrical basketry press or tipiti which is suspended from a house beam or tree branch by a loop. It is so constructed by diagonal weaving that when stretched lengthwise by hanging a weight on it or by using a lever at the lower end, its diameter decreases, so compressing the contents (Dole, 1956; Lowie, 1963). Less sophisticated devices are traditionally used in West Africa and the pressing stage takes longer, 3-5 days generally, compared to just overnight using the tipiti. The grated Cassava mash is placed in jute sacks or cloth bags and squeezed by a variety of techniques, often by simply placing heavy stones or logs on top of the sacks for 35 days (Affran, 1968; Anasanwo, 1942; Doku, 1969; Dovlo, 1973; Jones, 1959; Oke, 1968; Vignoli and Cristau, 1950).
After this stage the processes again converge in the two localities, the partially dried cassava being sifted to remove any coarse fibres and heated over a fire in a wide shallow pan with continuous stirring to prevent the formation of lumps, resulting in a free flowing granular meal (Doku, 1969; Jones, 1959; Schwerin, 1971). Gari and farinha can be stored for several months if properly dried during manufacture and kept dry during storage (Jones, 1959; Schwerin, 1971).
Most commonly gari and farinha de mandioca are eaten as a gruel prepared by mixing the meal with water or mixed with less water as a dough, accompanied by soup or stew. The gruel may be sweetened with sugar or accompanied by groundnuts or grated coconut. In Brazil, farinha is often sprinkled as a condiment on a variety of foods and is known by the name farofa when used in this way (Affran, 1968; Doku, 1969; Ekandem, 1961; Schwerin, 1971; Jones, 1959) .
Farinha can also be prepared from roots which have been soaked for 3-8 days in water before grating and is then known as farinha d'agua or farinha puba (Anonymous, 1971; Goldman, 1963; Lecointe, 1922; Metraux, 1963; Schwerin, 1971 ; Tastevin, 1954).
In South America a second popular product is made from grated and pressed cassava roots, a "bread" known variously as cassave, casabe, beiju or couac depending on the locality (Jones, 1959; Lecointe, 1922; Lowie, 1963; Metraux, 1963; Montaldo, 1979; Reynavaan and Vos, 1954; Schwerin, 1971; Tastevin, 1954). When heating the partially dried cassava pulp on a griddle, instead of stirring continuously as for farinha the pulp is pressed into a thin layer and toasted on each side forming a large flat circular cake. This can be eaten fresh while still soft inside (Goldman, 1963) but is more commonly sun-dried several days until hard all through in which state it can be stored for several months (Schwerin, 1971).
The extraction of starch from cassava roots is a technique used widely throughout the cassava producing regions and basically the same process is used everywhere. Grated cassava roots are washed with water and the starchy liquid strained through a cloth into a container where the starch is allowed to settle out. The water is decanted off and the starch dried and used for baking, for boiling as dumplings or stored until needed (de la Cruz, 1970; Doku, 1969; Ekandem, 1961; Hiranandani and Advani, 1955; Sturtevant, 1969). In South America starch is traditionally obtained as a by-product of the manufacture of farinha, the starch being allowed to settle out from the juice squeezed out of the grated cassava in the tipiti (Schwerin, 1971) . Starch is generally baked into cakes, called sipipa by the Caribs of tropical America (Schwerin, 1971), roskete in the Trust Territories of the Pacific Islands (de la Cruz, 1970) or pot bamie in Jamaica (Sturtevant, 1969). In parts of Nigeria, starch is collected from roots that have been soaked several days, then rubbed through a sieve into water in which the starch settles out, the water being decanted off and the starch boiled, pounded, reboiled and made into a dough known as fufu or other products (C.K. Coursey, 1973).
In many parts of the world cassava starch is further processed into what is known as tapioca in world trade. Wet starch is heated in a pan while stirred continuously until the grains burst and gelatinise into globules. This is generally consumed as a sort of porridge mixed with milk or water and it can also be stored (Affran, 1968; Anonymous, 1933; Hanson, 1939; Lecointe, 1922; Oke, 1966; Schwerin, 1971). This product is, however, little used in traditional societies.
Another dried product which should be mentioned is the traditional Philippine product known as cassava rice or landang (Cedillo, 1952). This is made either from roots which have been peeled and soaked in water for 5-7 days and then macerated and air-dried, or from freshly grated roots which have been pressed to squeeze out the juice. The pulp from either method is placed into a winnowing basket and whirled until pellets are formed. These are then dried on a mat and steamed in a coconut shell or on screen mesh placed over a vat of boiling water, after which they are sun-dried for 3-5 days and stored until needed. They are said to keep for 3-6 months in a cool, dry place before going mouldy. Landang can be eaten without further cooking but if preferred it is soaked, boiled, re-soaked, mixed with coconut milk and reboiled.
In tropical America, particularly the Amazon lowlands, cassava beers are an important product and these are also prepared in parts of Africa but on a much more limited scale. In South America, fermented cassava beverages are commonly called kashiri or chica (the term chica is also applied to maize beers) and are prepared by a number of different techniques often involving mastication of the cassava root or one of its products. Mastication has the effect of speeding up fermentation due to the action of the salivary enzymes which initiate a conversion of starch to sugar. Cassava bread is often used as a basis for the preparation of beverages; left to ferment for several days after first moistening in water or masticating and sometimes toasting and then mixing with water it produces an intoxicating drink (von Hagen, 1949; Montaldo, 1979; Schwerin, 1971). Alcoholic beverages are also made from roots which have been soaked in a flowing stream for a week during which time they ferment (Schwerin, 1971), from grated cassava left to ferment under leaves (Montaldo, 1979) and from boiled pieces of cassava which are first chewed, mixed with water, heated and left to ferment in jars half buried in the ground for 2-3 days (Metraux, 1963). Both alcoholic and non-alcoholic beverages are also made from the cassava juice or yard collected during the processing of farinha (Schwerin, 1971) .
In Uganda cassava beer is made from cassava flour which is mixed with water and left to ferment for a week, after which time it is roasted over a fire, put into a container with water and yeast and left for another week. The liquid is then drained off, sugar added and left for a further 4 days before drinking (Goode, 1974).
Another important use of the cassava juice or yari squeezed out of grated cassava is in the preparation of a spiced sauce known as cassareep in the West Indies, tucupy in Brazil and kasiripo in Surinam (Anonymous, 1933; Hanson, 1939; Lecointe, 1922; Reynvaan and Vos, 1954). The yard is seasoned with peppers, pimento, garlic, herbs, etc. and boiled to a thick syrupy consistency. In the Caribbean cassareep forms the basis of the "pepper pot" in which meat, fish and vegetables are cooked and maintained for years by boiling each day and adding further ingredients as necessary (Anonymous, 1918).
In the South Pacific the fermented product known as ma is normally made from breadfruit and sometimes from banana or taro (see sections below). However, on the Solomon Islands of Anuta and Tikopia cassava forms the basis of this product which is known here as ma manioka or masi manioka (Yen, 1973b; 1978). The roots are soaked in water for a few days on Tikopia and when soft, peeled, squeezed and ensiled in pits lined with leaves. On Anuta there is no suitable surface water for soaking and so the roots are placed in pits and left for a few weeks, then recovered, peeled and returned to the pits for a further period. To prepare for consumption, ma is baked alone or with freshly pounded starchy roots or fruits.
There are numerous other products prepared from the cassava roots in various countries of the world and these have been catalogued more fully in a recent review (Lancaster et al., 1982). However, the products discussed here are among the most important in terms of their contribution to world diets, and serve to indicate the range of traditional processing techniques and also the range of storable products that can be prepared from the cassava root.
The processing of cassava by the traditional techniques is often a very laborious and timeconsuming occupation and is invariable carried out by women. A survey of several villages in Nigeria showed that it takes an average of 90 hours to produce a 103 kg bag of gari, the whole process from uprooting the cassava and transporting it from the field through to the "gasifying" being done by women alone or in groups. The most unpleasant part of the process was considered by the women to be the "gasifying" as during this they are exposed to steam for many hours at a time (Williams, 1979). Similarly, in South America, the women of many Amerindian groups spend a large proportion of their time both in the cultivation and processing of cassava. For example, the daily preparation of foods such as cassava bread, which involves arduous tasks such as grating the raw roots by hand, may take up to 75% of a woman's working time and during festivals her whole time may be devoted to the preparation of special alcoholic beverages from cassava (Goldman, 1963).
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