7. Harvest, post-harvest and value addition
Food for the household, feed for livestock, and raw material for a wide array of value-added products, from coarse flour to high-tech starch gels – cassava is a truly multipurpose crop.
In Central Africa, tender young cassava leaves are comsumed as a vegetable
Cassava roots may be harvested at any time between 6 and 18 months after planting. During food shortages, they can be harvested as needed, often one plant – or even one root – at a time. Once harvested, roots are consumed directly by the farm household, fed to livestock or sold for processing into a wide array of value-added products. However, harvested roots deteriorate rapidly and processing must begin within 48 hours.
The root is not the only part of the plant that can be put to good use. Cassava leaves can be cooked as a vegetable or used for raising silkworms. The green part of the upper stem is fed to cattle and buffaloes, and the leaf-blades to pigs and chickens. Stumps are burned as fuelwood, and woody stems are ground-up and used as substrate for growing mushrooms.
Food for direct consumption. Young cassava leaves are regularly picked and cooked for human consumption in Central Africa. The tender leaves contain up to 25 percent protein and are a valuable source of iron, calcium, and vitamins A and C. The market value of cassava leaves in areas where they are consumed is often higher than that of the roots.
Cassava roots are washed and peeled before being boiled, steamed or roasted. In West Africa, grated roots are fermented, then roasted to produce a granulated flour called gari, or sun-dried, milled and mixed with water to make a stiff dough called fufu. In Indonesia, thinly sliced roots are fried, covered with spices and sold in local markets.
High quality cassava flour (or HQCF) is not fermented and can be used as substitute for wheat flour in bread and confectionary. Native starch extracted from the roots is used in many food products. Starch extraction can be done at almost any scale – in backyard artisanal production units and in large-scale fully mechanized factories. Many artisanal starch production units operate in Cambodia, India, Indonesia and Viet Nam, with daily output of 60 kg per worker. Semi-mechanized processing can yield up to 10 tonnes a day.
Industrial uses. Modified cassava starch is produced, mainly in Asia, for use as feedstock for production of sweeteners, fructose, alcohol and monosodium glutamate, and in plywood, paper and textiles. In modern starch extraction plants, daily output is as high as 300 tonnes.
Increasingly, cassava is also being used for production of fuel ethanol; in 2012, China produced 780 million litres of bio-ethanol from 6 million tonnes of dried cassava. Two recent cassava mutations could expand considerably cassava’s use in industry: an induced mutation with very small starch granules, which offer a faster rate of hydrolysis than other starches, and a spontaneous mutation with amylosefree starch that rivals premium “waxy” maize starch.
Animal feed. Both the roots and leaves of the cassava plant can be used as on-farm animal feed or as an ingredient in commercial animal feed. In Asia, small farmers and their marketing partners provide large amounts of cassava chips for the animal feed export industry. Sundried chips are milled into a powder that can be mixed with vegetable protein sources to make a nutritious animal feed. Animals raised on cassava diets have generally good health, good disease resistance and a low mortality rate, and require few if any antibiotics in their feed.
Dry cassava leaf meal (or “cassava hay”) is usually obtained by cutting the plant tops at 2.5 to 3-month intervals during the cassava growth cycle. Research has shown how supplementation with 1 to 2 kg of cassava hay per animal per day increases the milk yields of dairy cows and may enhance milk quality and storability.
Leaf silage is made from chopped leaves mixed with small amounts of cassava root meal or rice bran. Sealed in air-tight containers, the leaves ferment and after about 90 days are ready to be fed to pigs and cattle. In experiments in Viet Nam, a diet containing 15 percent ensiled cassava leaves improved the daily weight gain of pigs and reduced their feed costs by 25 percent.
Save and Grow: Cassava (FAO, 2013) can be purchased from email@example.com