Tapioca. Bitter cassava, Manihot utilissima. Sweet cassava, Manihot palmata.
Tapioca.—Under this name the U. S. P. formerly recognized the starch grains obtained from the bitter cassava (Manihot utilissima Pohl), and the sweet cassava (M. palmata var. Aipi Pohl) (Fam. Euphorbiaceae). The starch is extracted from the thickened root and is known in commerce by the names of Cassava, Tapioca or Manioca Starch, and as Bahia, Rio or Para Arrowroot. The plant is cultivated in Brazil and other parts of tropical America. It is also grown in Florida and other of the Southern States. In the production of the starch from the bitter cassava the hydrocyanic acid which is present in fresh roots is entirely eliminated by the process of washing and drying.
The root of the sweet cassava may be eaten with impunity; that of the bitter, which is the most extensively cultivated, abounds in an acrid, milky juice, which renders it highly poisonous if eaten in the recent state. Henry and Boutron Chalard affirm that the bitter cassava contains hydrocyanic acid (J. P. G., xxii, 119), but Peckholt claims that its poisonous effects are due to manihotoxine (Ph. Rund., iv, 1890).
The preparation of tapioca in Malacca is thus described by James Collins: The fresh root-stocks are thoroughly washed in tubs in a constant stream of water by the Chinese, and then peeled like turnips; they are then sliced in one machine and pulped in another, the pulp being removed in cane baskets to large wooden frames, with calico bottoms; a powerful stream of water is allowed to fall upon the pulp, a sifting motion being communicated to the strainer; as the starch is washed out, it is received into inclined troughs, and, while in a state of suspension, run into settling vats. There it is stirred and washed, and, while moist, it is removed to the drying room. Two kinds of tapioca are prepared. The flour is made by heating slightly by fires placed underneath; it is constantly stirred and turned over with iron shovels, to prevent agglutination and insure equal drying. Granular tapioca is made as follows: A long range of quallies, or small, shallow iron pans, are slightly tilted forward on ledges of brickwork, and heated with a wood fire. Each operator has a quallie and fire to himself. Taking a quantity of damp starch, he stirs it round and round with an iron shovel, and the heat is sufficient to cause the tapioca to become agglutinated together in small masses, and coated with dextrin. The drying is done with great skill over an open fire. (C. D., 1884.)
Tapioca is in irregular, hard, white, rough grains, possessing little taste, partially soluble in cold water, and affording a fine blue color when iodine is added to its filtered solution. The partial solubility in cold water is owing to the rupture of the starch granules by heat. Examined under the microscope, the granules appear somewhat plano-convex or bell-shaped and more or less compound. The individual grains vary from 0.006 to 0.030 mm. in diameter and have a distinct central circular or radiating cleft. They polarize light strongly, showing a distinct cross. Tapioca meal, called sometimes Brazilian arrow-root, and by the French moussache, is the fecula dried without heat. Its granules are identical with those already described. Being nutritious, and the same time easy of digestion and destitute of irritating properties, tapioca forms an excellent diet for the sick and convalescent. It is prepared for use by boiling it in water. Lemon juice and sugar are usually grateful additions, and in low states of disease or cases of debility it may be impregnated with wine and nutmeg or other aromatic.
A factitious tapioca is found in commerce, consisting of very small, smooth, spherical grains, and supposed to be prepared from potato starch. It is sold under the name of pearl tapioca.
Cassaripe is the thickened gum obtained from the root of the bitter cassava, which is said to be innocuous and so actively antiseptic as to be habitually used in Brazil for the preservation of meat. According to S. D. Risley (Phila. Med. Journ., 1899), the 10 per cent. ointment of cassaripe is useful in suppurating conjunctivitis and ulcers of the cornea, applied with gentle massage three or four times a day.