Tbe bruising is very simply performed in a roller mill, the iron rods being adjustable, and a smaller roll revolving above, and serving to regulate the feed. The mill must be set so that it will bruise every grain without crushing the starch granules.
The bruised grain is conveyed for fermentation to largo oaken cisterns, which, when new, require to be filled with boiling water for three days to extract the tannic acid. For fermentation, the grain is stirred up with pure water in summer, or soured water iu winter, the temperature is maintained at about 20° (68° F.), and the operation lasts some 11 days. Daring its contiuuance, the mass is well stirred up. Finally the scurn subsides, the surface becomes covered with a fungus (Penicillium glaucum), aud the mass is " ripe." The result of the fermentation is that the gluten has been so far decomposed as to liberate the starch granules; care must be taken to prevent its over stepping this limit, and affecting the starch granules themselves.
The impure liquor is drawn off from th,o starch mass, and the latter is transferred to washing drums (Fig. 1290) for evaporating the starch from the associated impurities. The side-walls b of the drurn aro of wood with iron spokes, the drum itself being a perforated copper plate ; a per forated pipe c passes through the stuffing boxes of the drum, and is surrounded by a seeond easing d, also perforated. The drum is emptied and filled by the door a. The starch-milk flows from the drum into the box f, whieh runs on rollers, and thence into the depositing-tank g.
Here the gradual separation of the starch takes place under the influence of agitation and subsequent rest. All but the starch, whieh forms the lowermost layer, is removed. The starch is then passed through very fiue hair sieves, and again stirred up v, ith pure water, and again allowed to deposit after some agitation. It is more convenient to effect the sifting under water. The final deposition takes place in oblong troughs, with convenient taps for letting off the liquids. The refining is not carried beyond the point when the starch
ceases to show an acid reaction on litmus-paper. The washing is frequently done in centrifugal machines. Lastly, the starch is dried, first partially by laying the cakes under bricks or gypsum slabs, or by means of air-pumps, and completely in a drying-room at 60° (140° F.).
Iu prepariog wheat-starch without fertnentation, thc grain is steeped, bruised, and washed, the last operation being best done in a centrifugal machine. The process is not a general one, in spite of its affording the gluten as a by-produet.
The preparation of starch from wheat-flour (Martin's method) has many advantages over the ordinary plan. The flour is kneaded into a stiff dough with water, and, after one or two hours, the dough is washed in a flue sieve under a jet of water till all the starch has escaped as a milky fluid. The washing is best effected by a machine such as is shown in Fig. 1291.
The troughs a contain water, and are replaced at b by wire cloth drawn over a wooden frame. Grooved wooden rollers are made to move across the bottom of the troughs, while constant jets of water play upon the dough. About one hour suffices for liberating the starch from 2 lb. of dough. The starch-milk flows off by a pipe into a receiver. The gluten is freed from surplus water by kneading under the rollers, and is then removed for utilization as food.
Bibliography.—J. Wiesner, ' Die Roltstoffe des Pflanzen reiches ' (Leipzig: 1873); R. J. Bernardin, 'Classification de 250 Fecules ' (Ghent : 1870); P. L. Simmends, Tropical Agriculture ' (London : 1877) ; C. Seheibler, Starkemehl Industrie ' (in A. W. Hofmann's Cheraische Industrie,' III. Heft, Brunswick : 1877); Fltickiger & Hanbury, Pharnlaeographia ' (London : 2nd ed., 1879); Frankel & Hatter, Starch, Glucose, &c.' (Phila delphia: 1881); F. Rehwald, Stiirke-Fabrikatien, &c.' (Leipzig) ; Bentley &' Trimen, Medicinal Plants,' pp. 265,266,278 (Lond.: 1875-80); Pereira's Materia Medica,' 5th ed., Vol. ii., part 1.