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Cassava

Agronomic Characteristics

Cassava is a very hardy crop that will adapt to a wide range of growing conditions, soil types, and fertility levels. It is particularly noted for its ability to yield on soils of extremely low fertility, and is often grown where all other crops have failed. Cassava cultivation is relatively simple with very little necessary land preparation and a simple planting technique of merely inserting stems into the soil. However, demanding labour is required at harvest time in digging the deeply embedded roots from the soil. Cassava is very popular with many subsistence farmers because of its ability to yield more calories of food per unit input of labour than probably any other crop. A growing season of 6-10 months is usually needed for maturing

Antinutritional Factors

Raw cassava contains cyanogenic glucosides, particularly linamarin and lotaustralin, which are converted to prussic acid (hydrogen cyanide, HCN) when they come in contact with linamarase, an enzyme that is released when the cells of cassava roots are ruptured. Good processing and cooking methods reduce the cyanide levels, and acute cyanide toxicity rarely occurs. Chronic cyanide toxicity occurs when cassava consumption is very high (7 kg or more of fresh roots per day over long periods), especially where iodine and/or protein consumption is very low.

Utilisation and Processing

Cassava roots are rich in energy and contain mainly starch and some soluble carbohydrates, although poor in protein. It has been estimated that people eat more than 60% of all cassava produced, and about a third of the harvest is fed to animals, while the rest is transformed into secondary products. It can be processed into gari (West Africa) , fufu (Ghana) , chikwangue (Central Africa), flour for bread, etc.

Drying of cassava roots is an important step in reducing weight and microbial spoilage. The chips are spread on mats, cement floors and roofs of houses to sun-dry. After that they are milled by pounding with a pestle in a wooden mortar or by using a grindstone, followed by sieving through a screen. Mechanical mills are also used sometimes for efficiency.

Fermentation is another important process in making cassava products. The importance of the fermentation stage in cassava processing is linked to the reduction of cyanogenic glucosides, the introduction of flavours and the lowering of the pH in the fermented product.

Gari: Roots are peeled, washed and grated. The mash is placed in bags and squeezed (either by tying it up with sticks and continuously tightening the ropes or by a variety of screw or hydraulic presses) for a minimum of 48 hours to allow detoxification by fermentation. The dough is fried dry and stored in bags and sealed plastic packages, to be rehydrated and eaten with soups, sauces, and sometimes sugar.

Fufu: The root is peeled (sometimes after soaking in water) and boiled or steamed, followed by pounding with a pestle in a mortar into fufu, which is eaten with a soup containing fish, meat and/or vegetables.

Chikwangue: The cassava is soaked in water for several days until it softens; the root is then peeled, macerated and sieved to remove fibres. The paste or dough is wrapped in banana leaves and eaten usually after boiling.

Industrial products such as starch, glues, cassava beer, cassava alcohol and cassava vinegar are obtained from various processing operations using cassava.

Starch is obtained when the roots are peeled, washed and finely grated. The starch is filtered from the fibre and then collected either by sedimentation or centrifugation, dried and milled into fine powder. Starch is used in textiles, foods such as bread, and in the fructose syrup industry. Cassava starch is a substrate for dextrins used in the manufacture of glues. Cassava flour is used as an adjunct in the beer-brewing industry. Cassava alcohol is distilled after the alcoholic fermentation of cassava. The use of bacterial acetic acid (Acetobacter spp.) in the fermentation of boiled ground cassava after fermenting with starter rice yeast and cellulase enzyme leads to the production of cassava vinegar.