Cassava is a staple crop and is particularly
important in Africa and South America. It is a
perennial shrub that grows to approximately 2
metres tall and has the ability to grow on marginal
lands in low-nutrient soils where other crops do not
grow well. It is also fairly drought tolerant.
It is grown for its enlarged starch-rich tuberous
roots. The amount of carbohydrates contained in
dry cassava root is higher than other staple crops,
such as maize or cereals but, by contrast, the
protein content is very low.
Figure 1: The cassava root
Although cassava is a staple it is poisonous in its
Illustration: Neil Noble/Practical Action
raw state as the plant contains cyanogenic
glucosides. These glucosides are converted to hydrogen cyanide (HCN) by an enzyme called
linamarase, which is also present in cassava and acts on the glucosides when the plant cells are
ruptured either when it is eaten or during processing.
The amount of cyanide present depends on the variety. There are two main types of cassava,
bitter and sweet. While, in general, bitter varieties have higher levels of cyanide it must not be
assumed that all sweet varieties have low cyanide levels. The cyanide levels range from 10 to 450
mg/kg of fresh root. The poison tends to be more concentrated in the skin of the root.
The cyanide is readily removed during processing, resulting in a safe and versatile product that
can be made into many different foods and non-food products. After proper processing a final
residue of hydrogen cyanide will remain at very low concentrations but it does not cause any
problem regarding the consumption of cassava products.
Versatility of cassava
Traditionally cassava has been regarded as a subsistence crop for low-income families - providing
high levels of carbohydrates during shortages of other crops because of its tolerance to drought
and ability to grow in poor soils. Recently the view of cassava as simply a subsistence crop has
begun to change and there is growing interest in developing its commercial potential through
improved varieties, increased productivity, harvesting and processing technologies. Along with the
increased production of cassava, new markets and uses for the crop are being developed.
Cassava roots are processed in many different ways to make it edible, to change its
properties, remove cyanide and improve its storage capacity.
Cassava is made into flour, commonly known as gari in West Africa and Farinha in Latin America,
which is an ingredient in many recipes and used to make cassava bread or to replace up to 10%
wheat flour in conventional bread. In many cassava-producing countries there is interest in
reducing the wheat flour importations. Brazil incorporates 2% of cassava flour in wheat flour
bread and Nigeria has recently made it a requirement to have 10% cassava flour in its bread.
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