CORNFLOUR. The starch of maize (Indian corn) refined for use as a foodstuff . A grain of maize has a complicated struc ture, consisting mainly of an em bryo plant and starchy food to sustain its early growth. The endosperm or store of food is a mass of minute granules of starch, corn gluten and protein. Each granule is a unit of definite shape and size, and the cell in which it lies might be compared to the cells of a honeycomb, only in finitely smaller; this is the common characteristic of the grass family.
The main problems of the manufacture of cornflour are : the separation of the starch granules from the germs, hull, and gluten; (2) the purifying of these granules; and (3) the selection of those granules which possess in the highest degree purity and strength, i.e., the quality of forming a stiff paste when boiled with water or milk. To obtain the best result, the grain used must be carefully selected. Maize is now grown in many parts of the world. The chief exporting countries in the past have been the United States, the Danubian provinces, and Argentina. More re cently maize has been shipped from South Africa and Rhodesia, West and East Africa, and to a lesser extent Rangoon, Egypt, and elsewhere.
The grain first undergoes dry cleaning, all dirt and dust being removed. It is then scoured in water to remove the last traces of foreign matter. The clean grain is carried by elevators and con veyors to steeping tuns. Steeping is done with a dilute solution of sulphuric dioxide gas. This prevents fermentation and helps to soften the kernels so that the germs are easily separated and the hull loosened. The steep water is evaporated and valuable solu bles recovered. The time of steeping and the temperature are important factors. The grains, brought to the right degree of soft ness, are ground and split, to free the germ from the rest of the grain. The broken mass passes into a germ separator, where the germ, being lighter, is floated off. The germ, which contains about 4o% of oil, is then dried and sent to the oil mill for the extraction of the oil. This oil, which in its crude state is not fit for human food, can by careful refining be made suitable for edible purposes, and is largely used for cooking, baking and as salad oil. After the extraction of the oil, the residue of the germ is made into a cake which is of special value for fattening cattle and sheep and is sold under the name "maize germ cake." The germ eliminated. the corn is finely ground in a wet state, and the starch granules separated from the coarser constituents, which form a valuable cattle food. The milky starch thus ob tained is further refined by passing over a long series of inclined "runs" or tables. The starch granules, being heavier than water, fall and settle on the smooth surface of the runs. There is, how ever, in the liquid, along with the comparatively pure starch gran ules, a certain quantity of yellow starch matter or corn gluten (with other impurities) which, being lighter than the starch, is kept in suspension, and eventually flows over the tail end of the runs and is collected to be mixed into cattle food. Thus a further separation has been effected, but the pure starch required for cornflour has not yet been obtained. Periodically the flow over the run is stopped, and the settled starch is cut out from the runs into vats, which have a central stirrer. When a sufficient quantity has been collected in a tun, clean fresh water is run in, along with caustic soda liquor, and the stirrer is set in motion, so that by degrees the starch is lifted into suspension. Certain of the nitro genous elements of the grain, which are intimately mixed with the starch in its present state, are now dissolved away by the caustic liquor. After stirring, the starch is pumped to another tun in the washing house, where it is allowed to settle, the solid starch gran ules slowly falling to the bottom, and forming a hard compact mass, on the surface of which there settles out a small quantity of softer yellow matter (called "the tops"). This settling takes from two to four days. The "tops" are removed, and the fine residuum washed several times. Next comes drying, and when this is done, the flour is raked down into hoppers, from which it is drawn off into bags. This is now finished cornflour in the "crisp" state, and all that remains to be done is to pulverize it. This is done in a special mill, but even here care has to be taken to eliminate any foreign particles. A careful sieving therefore forms the actual final operation.