CASSAVA. Cassava, or manioc (Manihot esculenta ), is a root crop native to tropical America that is now consumed by millions of people throughout the tropics, and is used in food preparation in many industrialized processes. Although it is not well known outside the tropics, cassava now accounts for about 30 percent of the world production of roots and tubers. It is an exceptional producer of carbohydrates and a plant better able to tolerate seasonal drought than other major food crops.
The cassava plant is a perennial woody shrub that grows from about one to three meters in height. The leaves are palmate (hand-shaped) and dark green in color. The cone-shaped roots are starch storage organs covered with a papery bark and a pink to white cortex. The flesh ranges from bright white to soft yellow. Over five thousand varieties of cassava are known, each of which has its own distinctive qualities and is adapted to different environmental conditions.
The cassava plant is hardy and better able to tolerate drought and poor soil conditions than most other food plants. It can grow in extremely poor, acidic soils because it forms a symbiotic association with soil fungi (mycorrhizae). It is also one of the most productive food plants in terms of carbohydrate production per unit of land, and unequalled in its ability to recover when foliage is lost or damaged by diseases or pests.
The cassava plant is somewhat unusual, and even infamous, because both the roots and leaves can be toxic to consume. The toxicity of cassava is due to the presence of cyanogenic glucosides (compounds of cyanide and glucose) which liberate hydrogen cyanide (HCN) ), a potent toxin, when the plant tissue is damaged. Cyanogenic glucosides are found throughout the plant and in all varieties of cassava. Varieties referred to as "sweet," or low-cyanide, have low levels of cyanogenic glucosides in the flesh of the root and can be peeled and cooked like other root vegetables. Those referred to as "bitter," or high-cyanide, have higher levels of cyanogenic glucosides throughout the root (peel and flesh) and require more extensive processing before they are safe to consume. A number of different processing techniques are used (grating, fermenting, sun drying), all of which serve to damage the plant tissue and hence cause the liberation and volitalization of HCN. The potential toxicity of cassava foods depends on the effectiveness of processing and preparation techniques; high-cyanide roots can be processed to remove all most all traces of cyanide-containing compounds. Many farmers prefer to cultivate the high-cyanide varieties for reasons that are not entirely clear.
Cassava was domesticated sometime in the distant past, maybe five thousand years ago. Exactly where is not known, but the current consensus is that domestication took place somewhere in Central or South America, perhaps along the southern border of Brazil, where wild relatives of cassava are currently found.
Cassava was the staple crop of the Amerindians of South America when the Portuguese arrived in 1500 just south of what is known as Bahia, Brazil. The Amerindians living in the area were the Tupinamba, who relied on cassava as a dietary staple, processing it into bread and meal using techniques similar to those still used by Amerindians in the twenty-first century.
When the Portuguese began to import slaves from Africa in about 1550, they used cassava in the form of meal (farinha) to provision their ships and began cultivating cassava at their stations along the coast of West Africa soon afterward. From their stations near the mouth of the Congo River, cassava diffused to all of central Africa. The Portuguese were also responsible for introducing cassava to East Africa, Madagascar, India, Ceylon, Malaya, and Indonesia by the 1700s.
Cassava was probably first introduced into Asia during Spanish occupation of the Philippines and was distributed throughout tropical Asia by the beginning of the nineteenth century. Expansion of cassava cultivation was pushed by colonial administrators who saw cassava as a famine reserve (especially the Dutch in Java, and the British in India), and as an export commodity (Malaya and Java in the 1850s).
Procurement and Production
Cassava is typically grown by small-scale farmers using traditional methods, and farming on marginal lands not well suited to other crops. It is propagated by planting stakes cut from the woody stems of mature plants. These plantings require adequate moisture during the first two to three months, but after that they are relatively drought resistant. Cassava roots mature to harvestable size in six to twelve months depending on variety and ecological conditions, and can be harvested at any time in the following two years, a harvest window that provides farmers an unusual degree of flexibility. To harvest the plants, farmers typically cut off the top three-quarters of the plant, and then pull up the roots and separate them from one another. Mechanical harvesting is still relatively rare.
Because fresh cassava roots deteriorate rapidly (within three to four days) after harvesting, they are usually consumed immediately or processed into a form that has better storage characteristics. Fresh roots (low-cyanide) destined for distant markets can be sealed in wax, packaged in plastic bags, or frozen to prevent deterioration. Leaves can be harvested at any stage of the growth of the plant, but typically only the youngest leaves are picked. The leaves deteriorate rapidly after harvesting and so are generally cooked the same day.
Cassava roots are prepared into an amazing variety of foods. Traditional preparation techniques vary by region, and by ethnic group within a given region.
South America. For Amerindians, the most common ways of preparing high-cyanide cassava were as a bread (casabe, cazabe, beiju ), a roasted granular meal (fariña, farinha), and as a beer (chicha ). In the northwest Amazon the bread is a large, thick (one inch or more) flat bread made by peeling and grating the roots, and then sieving the grated mash with water to separate the liquids and starch from the more fibrous portion. The starch is allowed to settle, and the liquids decanted off the top, then boiled to make a drink (manicuera ). The starch and fibrous portion of the roots are stored separately and allowed to ferment for forty-eight hours before being dewatered, and then recombined and baked on a large clay griddle. In Venezuela and Guyana the bread is a thinner, hardtack-like bread made without the starch extraction step.
Farinha is made by soaking the roots of yellow-fleshed, high-cyanide varieties in water until they ferment. The roots are then peeled, grated, mixed with fresh grated roots and the mixture allowed to ferment for a week or more. The mash is then dewatered, sprinkled onto a hot griddle, and roasted while being stirred. The resulting product is a dry granular meal that can be stored almost indefinitely. It is most commonly consumed as chive, a drink that is made by putting a handful of meal in water and swirling to mix. Well-made meal can expand five times in volume and results in a full feeling.
Chicha, a mildly alcoholic beer, is made from both low-cyanide and high-cyanide cassava. With low-cyanide varieties it is prepared by peeling, cooking, and mashing the roots, then adding water and some masticated roots and allowing the mixture to ferment. With high-cyanide varieties it is prepared from manicuera (the cooked juices) and a very thin bread, some of which is masticated, and other cooked roots or tubers.
In the national cuisines of South America, low-cyanide cassava is used as a vegetable (boiled, or boiled and fried). In Brazil, farinha is part of a number of traditional dishes, and in Colombia several breads are made with the fermented starch of high-cyanide cassava.
Africa. Cassava is the second most important food crop in sub-Saharan Africa. The majority of the cassava-based foods made in Africa rely on fermentation in one form or another. Two common products are gari, a granular meal similar to farinha, and fufu, a sticky dough made by pounding cooked or fermented roots into a paste. Other products include chikwange or baton de manioc, a steamed/boiled paste made from soaked roots, and lafun, a flour made from soaked roots.
Asia. Cassava roots are prepared in most Asian countries by boiling, baking, and frying. Another widespread practice is to peel, slice, and sun dry the roots and then grind them into a flour. The flour is then used to make porridge, or other traditional foods like chappatis and dosas (India), bibingka (Philippines), and a rice-like product called landong (Philippines). Commercially produced cassava starch is exported as tapioca.
South Pacific. Boiling and baking are the most common techniques for preparing cassava roots. On some islands cassava is also used to prepare ma, a traditional fermented product typically made from breadfruit.
North America and Europe. The pure starch, or tapioca, extracted from cassava roots is commercially available as a flour, flakes, or pellets (pearls) and is used to thicken a wide variety of food products such as sauces, gravies, pie fillings, pudding, and baby foods. The well-known dessert tapioca pudding is made with the pearls, which become gelatinous, semi-transparent balls in the finished product, affectionately referred to as "frog spawn" by British schoolchildren.
Relations to Human Biology
Fresh peeled cassava roots are rich in carbohydrate (30–35 percent), and low in protein (1–2 percent) and fat (less than 1 percent). They have nutritionally significant amounts of calcium (50 mg/100g), phosphorous (40 mg/ 100g) and vitamin C (25 mg/100g). The quality of the protein is relatively good, and the starch is highly digestible. Fresh cassava leaves are a good source of protein (23 percent), vitamins, and minerals.
The cyanide-generating potential of cassava roots and leaves has been of considerable concern. Although traditional methods of processing are effective in reducing cyanide content to innocuous levels, inadequate processing, as sometimes occurs during famine and periods of social upheaval, or the rush to market, can lead to health problems, particularly cyanide poisoning.
In South America there is no evidence of acute or chronic cyanide toxicity associated with cassava consumption by Amerindians for whom cassava is a traditional dietary staple, even though some groups rely on varieties of cassava with a very high cyanide content. In other parts of the world, however, cassava consumption has been associated with cyanide toxicity and other disorders. Acute cyanide poisonings are relatively rare, but can be fatal. The cases typically involve the consumption of raw or inadequately processed cassava. The symptoms are dizziness, headache, nausea, vomiting, and diarrhea.
In Africa, cassava-based diets have been associated with two neurological disorders: tropical ataxic neuropathy (TAN) and konzo. Both occur among the rural poor on diets largely restricted to high-cyanide cassava. TAN is a disease characterized by ataxia (muscular incoordination), reduced sensory perception, and deafness. The onset is slow and the course progressive, and it is found primarily in adults over the age of forty. Konzo is a disease characterized by the sudden onset of spastic paralysis in both legs, which results in a slightly spastic gait in mild cases and a complete inability to walk in severe cases. It primarily affects children and women under forty, and tends to occur in areas under conditions of famine or near-famine when people have nothing to eat but cassava and their nutritional status is poor. Both of these disorders are relatively rare given the millions of people on cassava-based diets in Africa.
The cyanide found in cassava-based diets is metabolically detoxified to thiocyanate and therefore cassava consumers have higher than normal levels of thiocyanate in body fluids. This is thought to be beneficial in areas of West Africa where sickle-cell anemia is present because thiocyanate inhibits the tendency of hemoglobin molecules to sickle. It is problematic in areas of Africa where the dietary iodine intake is low because thiocyante blocks iodine uptake by the thyroid gland. In these areas, cassava consumption is associated with iodine deficiency disorders including goiter, cretinism, mild mental disorders, and other related conditions.
Cassava as a Symbol of Identity
Important food plants like cassava tend to be powerful symbols of social and cultural identity. These symbolic associations can be clearly seen in South America.
For the native people like the Tukanoan, cassava is one of the most important and highly valued foods, and is consumed with meals and most snacks. They believe that cassava was the first food; it was planted by the first woman to make bread for the first man. They consider the extracted starch, weta, to be the purest, whitest, and more nourishing of foods. The term weta also means the essence of something. For non-Indian subsistence farmers in the Amazon, farinha is an essential component of everyday meals and snacks, as well as an ingredient in special dishes. People will go to considerable trouble and expense to obtain it from the market when home-produced supplies run out because cassava is part of the fabric of everyday life, and consuming it part of their identity. In contrast, for Brazil's urban elite, farinha is only occasionally consumed as part of certain traditional dishes, and the everyday consumption of farinha is seen as a marker of lower class status and poverty.
Global and Contemporary
Cassava now provides about 30 percent of worldwide production of roots and tubers, and is the staple crop of over 200 million people in Africa alone. World production increased more than four-fold in the last two decades of the twentieth century, with most of this increase being in Africa. Cassava is a crop with enormous potential to provide food energy, and a crop that will play a particularly important role in areas like Africa where the production of adequate food is a serious challenge.
It is also a crop that has received relatively little attention from researchers in comparison to the dominant food crops of the green revolution—wheat, rice, and maize. However, efforts are underway to rectify the situation, and find ways to capitalize on cassava's strengths (high productivity, tolerance of poor soils and low rainfall, and relatively good resistance to pests and disease) and to improve its major shortcomings (rapid postharvest deterioration), and address its cyanide content. The following areas are particularly promising:
- The use of microbial biotechnologies (technologies that utilize organisms like fungi and bacteria) to improve production and the processing of traditional products and to develop new products. Cassava production depends on soil mycorrhiza (fungi), and processing technologies depend on a variety of fungi (Aspergillus, Saccharomyces, and others), and bacteria (mostly Lactobacillus and Corynebacterium ) to reduce toxicity, improve storage qualities, and achieve the desired taste and texture of cassava foods.
- The use of micropropagation (culturing of tiny masses of dividing cells) for the exchange of varieties. This is particularly important for cassava because the plant is traditionally propagated from vegetative stakes that can transmit disease.
- The use of genetic biotechnology for inserting new genetic material (DNA) into cassava varieties in order to improve quality and disease resistance.
See also Africa; Brazil; South America.
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Darna L. Dufour
Cassava root contains cyanide, and before it can be eaten it must be grated and left in the open to allow the cyanide to evaporate. The leaves can be eaten as a vegetable, and the tuber is the source of tapioca. See also cassareep.
cas·sa·va / kəˈsävə/ • n. 1. the starchy tuberous root of a tropical tree, used as food in tropical countries. Also called manioc. ∎ a starch or flour obtained from such a root. 2. the shrubby tree (genus Manihot) of the spurge family from which this root is obtained, native to tropical America.