Page:The New International Encyclopædia 1st ed. v. 07.djvu/843

FLOUR. century, and is still so common, especially in small ‘customs’ mills, that a brief description of this process of milling is given. The millstones are made of buhr-stone, a form of silica as hard as flint but not so brittle. They are usually from four to six feet in diameter, and each consists of a number of pieces strongly cemented and bound together with iron hoops. The grinding surface of each stone is furrowed or grooved, one side of each groove being cut perpendicularly and the other side being inclined to the surface of the stone. The grooves on each stone are furrowed exactly alike: thus the sharp edges of the grooves on the one come against those on the other, and so cut the grain to pieces.

Fig. 1 shows a section of a flour-mill. The millstones are at a, the lower of which is firmly fixed, and the upper is made to revolve, on a shaft which passes up through the lower one, at a speed of one hundred revolutions per minute, more or less. Motion is communicated by the spur-wheel b, which is driven by a water-wheel or other power. The grain, previously cleaned, is supplied to the millstones by means of the hopper, c, connected with which there is a valve, d, for regulating the supply. Passing through a hole in the centre of the upper millstone, it comes in between the two, where it is ground, and thrown out on all sides by means of the centrifugal force. The millstones are, of course, inclosed, and the flour passes down through the spout, e, to the worm at f, which carries it along to elevators, g. These raise it up to the floor, on which the dressing-machine, h, is placed. This is a cylinder, which was formerly made of wire-cloth of various degrees of fineness, and consequently separated the flour into different qualities, but no part of it large enough in the openings to let through the bran, which passed out at the end. Silk is now preferred to wire-cloth for dressing the flour. Hoppers, i, are placed below the dressing-machine, by means of which the flour and bran are filled into sacks; No. 1 being fine flour; No. 2, seconds; and No. 3, bran.

The third and final step in the development of milling processes was taken when rollers were substituted for stones to perform the grinding process. Iron rollers were generally used at Pest to grind wheat before 1840, and, under the name of the Hungarian system, rapidly spread throughout Europe. As early as 1810 Ignes Paur of Austria invented a middlings purifier which

is described below. It is claimed that in 1868-70 E. N. LaCroix, a French miller, independently invented a system of roller-milling similar to the Hungarian system, and installed it in one of the great flour-mills of Minneapolis. Its introduction marked an epoch in the production of American flour. The essence of this new process is the substitution for a single grinding between millstones of a succession of grindings between several sets of iron or porcelain rollers. The wheat is gradually reduced by running it through six or seven different sets of rollers, a thorough process of winnowing or sifting intervening between the grindings. As a musty odor and dark color are given to flour if it is heated during the process of manufacture, the rollers are kept cool.

Wheat is made up of a central portion of starchy cells, A in Fig. 3, surrounded by gluten cells, B, containing nitrogenous or proteid matter, which builds up tissue. The germinal portion shown at C contains phosphates, which possess great food value, as do the inner layers of the husk, D. The exterior coatings, which are of a fibrous or woody nature, are, on the other hand, quite indigestible while passing through the alimentary canal of a human being. That portion of the wheat between the central starchy portion and the husk is called the middlings. This is the most valuable portion of the wheat for making not only a nutritious but also a light bread.

Two grades of wheat are known to the miller: Winter wheat, or that sowed in the fall and coming up in the early spring; and spring wheat, which grows during the summer, and is harvested in the fall. The winter wheat, whose