Starch

Lentils .... . . . . .

Arrowroot (Maranta arundinacea) . 26-39 158 Tapioca (Jatropha manihot) . . . 25-40 156 Yams (Batata edulis) . . . • 25-35 Sago ...... . . . . 158 The storehouse, or starch-containing part of the plant, consists of a network of cells, within the walls of which the starch granules are closely packed together. The process of manufacture involves the rupturing of the enveloping cell walls and separation of the starch from the associated material by levigation.

Manufacture.

The manufacture of starch from roots and tubers is usually carried on in the locality in which they are grown ; that from potatoes on the continent of Europe, principally in Germany, France and Holland ; arrowroot, cassava and tapioca are prepared from the roots and tubers of the maranta and manioc plants in the West Indies and South America ; sago is manu factured from the pith of the sago palm and also from the yams or sweet potatoes in the East Indies and Borneo. Cereals can be more readily transported and stored, so locality is a matter of convenience ; thus rice is used as a raw material in England, France, Germany and Italy and other parts of Europe, while maize is used very extensively in North America, and in England, France and Germany. Wheat is not now largely employed.

The purposes for which starch is manufactured can be classified under three heads: (a) Industrial. These include sizing yarn and cloth in the tex tile industries ; dressing cloth ; thickening mordants and colours in calico printing; the preparation of British gums and dextrin, confectioners' glucose or corn syrups, and sugars for use in the fermentation industries.

(b) Food. Used alone in the form of cornflour, arrowroot, tapi oca, sago, etc., or in conjunction with other substances in the preparation of custard and blanc mange powders, macaroni, semo linas, sauces, cocoa, confectionery, etc.

(c) Laundry. In pipe or crystal form and powders, both "thick" and "thin boiling" preparations.

The suitability of starches from various sources for these pur poses depends on their cost, purity, the stiffness or viscosity of the paste they make with hot water and the size of the granules.

Potato, maize, rice and wheat starches are those chiefly used for industrial purposes; rice, maize, arrowroot, cassava and sago for foodstuffs; and the small granuled starches, rice and maize, are used extensively in the laundry owing to the fact that the granules are required to enter the texture of the linen or cloth before becoming gelatinized by the hot iron.

The general principles for dealing with all types of roots and tubers are substantially the same, but of course vary in their elaboration and efficiency in different parts of the world, and they also only differ to some extent in detail when cereals are being treated. They are briefly as follows :—The tubers first go through washing machines where earth, stones, sand and grit are removed; they then pass to a rasping machine where all the cells are com pletely ruptured. The resulting pulp is washed in a fine stream of water on fine-mesh brass sieves, which separate the starch from vegetable fibre, etc. ; the resulting milky starch liquor is run into vats to separate fine sand and grit by settlement, through fine silk sieves for further purification, and is finally allowed to run very slowly over long, shallow, wood troughs, runs or tables, where the pure starch settles out and the impurities pass off at the ends with the water. The pure white starch is washed from the runs by a jet of water and is pumped to either filter presses or hydro extractors, which remove all except about 40--45% of the water, leaving the starch in the form of a damp cake.

The cereals contain varying proportions of protein or gluten material associated with the starch, and special methods have to be employed in their preliminary treatment. The protein con tained in rice is found to be rendered soluble by very weak caustic soda solution, and advantage is taken of this in the production of starch from the raw material.