Cassava, manioc, mandioca, yuca, tapioca, sagu (Manihot esculenta)
EUPHORBIACEAE, Spurge Family
Cassava (Manihot esculenta) is a short-lived perennial, 1 to 5 meters tall. The origin of cassava is in South America, presumably eastern Brazil. From stem cuttings, the plant produces 5 to 10 very fleshy adventitious roots up to 15 centimeters in diameter. Young roots may have 30-35% starch by weight but very little protein or fat. As many as 300 million people in the tropics consume cassava daily. After planting a stem cutting, the crop does not have to be tended, and the roots are harvested 6 to 8 months later before they become woody. Cassava has the greatest yield of starch per acre of any crop in the world--often exceeding 20 tons of roots per acre!
Cassava was used in early pre-Columbian times in Colombia and Venezuela (3000 year B.P.) and Peru (2800 B.P.). This is remarkable, because cassava roots are bitter and deadly poisonous if eaten raw (bitter cassava, kii). The bitter principal is a glycoside of hydrocyanic acid (HCN), which occurs in the white, yellow, or red flesh. Very poisonous forms have greater than 100 ppm of cyanide. If ingested, HCN inhibits a respiratory enzyme and in a series of actions ultimately causes asphyxiation. The lethal concentration of HCN is 150 milligrams for a 50 kilogram adult. Native Americans learned that the deadly bitter principal could be removed by boiling or squeezing. Some cultivars lack HCN (sweet cassava, makasera; less than 50 ppm of cyanide), but this is highly variable and unreliable. Remarkably, there are certain cultures that show very strong preference for the most bitter, i.e., lethal, forms, and even intentionally use the most toxic tissues; in the end, the most poisonous forms often detoxify more completely than the milder forms, because there is more of the hydrolytic enzyme linarmarase to cause release of the hydrogen cyanide gas.
Sweet cassava is widely used and requires no special detoxification process; it can be eaten raw, sun-dried, kiln-dried, or cooked. For bitter forms, a common method of fixing peeled cassava is boiling pieces of the root for a long time--this drives off the poison as a gas. Some African and Amazonian cultures express the poison by squeezing the roots in a "tipitipi" or by pressing and pounding grated root with heavy stones or logs. Soaking roots is another technique. Once the cassava is detoxified, the root may be eaten warm, made into a past ("fufu" in West Africa), or prepared as a flour or meal ("farinha" or "gari") that can be made into bread, flat bread, biscuits, or tapioca. Tapioca is made by gently heating the pulp over an open fire until the starch agglutinates into small, translucent spheres. Tapioca is eaten dry or in puddings and sauces. This is the food of many impoverished people, who can barely afford to purchase a pound of tapioca for a few cents. In northern South America crude cassava meal (catevia) is grilled and baked into flattened bread, also called casave, which can be kept without spoiling for more than a year.
Starch from cassava can be used for producing sugar, acetone, and alcohol. Some people believe that Brazil can produce 20% of the alcohol its needs for motor fuel from cassava.