Modern machinery has taken the place of the old-time stones in the grinding of flour, although the two main divisions of the process remain the same, these being the crushing of the grain and the sifting out of the coarse portion. Milling now includes many stages in the process not possible with the cruder machinery of former times, and the present effects a greater number of separations and permits the miller to make a greater variety of products.
Figure 53 shows a dissected kernel of wheat, with its five layers of bran. Within these at B is a shell of glutinous matter, yellowish and of flinty hardness, and within this, but not sharply divided from it, lie the starch granules in a network of woody fiber, the germ lying at A. The milling process must remove the bran coats and the germ, and crush and roll the remaining portions to the necessary fineness. The germ if allowed to remain affects the color and keeping properties. The breaking and rolling are accomplished by steel machinery, and the final sifting is done through silk bolting cloth. By the new machinery about 70 per cent of the wheat is saved for food, 30 per cent being bran, "shorts," and other by-products used chiefly for cattle feeding.
Courtesy of Washburn Crosby Co.
Fig. 53. - A dissected grain of wheat.
Figure 54 shows the vertical section of a mill, simplified in the drawing that all the steps of the process may be clear. The diagram does not, of course, show the actual arrangement of the mill.1
The typical parts in a modern flour mill are as follows: (1) Scales, for weighing wheat as it is received. (2) Receiving separator, for separating other kinds of seeds from wheat. (3) Storage bins, for reserve supply of wheat in advance of mill requirements. (4) Mill separator, for further separating foreign seeds from wheat. (5) Scourer, for removing dust from wheat kernels. (6) Cockle cylinder, for removing all round seeds. (7) Wheat washer, for thoroughly cleansing the wheat. (8) Wheat dryer, for drying wheat after washing. (9) 1st break rolls, for rupturing bran, enabling bran and germ to be separated from interior. (10) 1st break scalper, for sifting middlings through bolting cloth to separate from bran. (11) 2d break rolls, for further loosening the middlings from bran. (12) 2d break scalper, for separating more middlings from bran. (13) 3d break rolls, for further loosening middlings from bran. (14) 3d break scalper, for final separation of middlings from bran. (15) Bran duster, for dusting low grade flour from bran. (16) Bran bin, for packing bran for shipment. (17) Grading reel, for separating middlings by sifting through various sizes of bolting cloth. (18) Dust collector and purifier, for cleaning and purifying middlings by air and sifting. (19) Smooth rolls, for grinding purified middlings very fine to flour. (20) Flour bolter, for sifting flour from purified middlings. (21) 2d reduction rolls, for further grinding of purified middlings. (22) Flour bolter, for separating flour from purified middlings of second grading. (23) Flour bin and packer, for packing flour for shipment. (24) Elevator, for raising products to the various machines.
1 Several of the large firms manufacturing flour issue pamphlets descriptive of the whole process, to be mailed free on application.
Courtesy of the Washburn Crosby Co. Fig. 54. - Simplified diagram of a flour mill.