Grinding is accomplished by one of four systems: (1) low milling; (2) Hungarian system, or high milling; (3) roller-milling; and (4) by a machine known as disintegrator.
In low milling process, grooved stones are employed for grinding. The stones are enclosed in a metal case, and provision is made within case for passage of air to prevent wheat from becoming overheated. The lower stone being permanently fixed, the upper stone being so balanced above it that grooves may exactly correspond, when upper stone rotates, sharp edges of grooves meet each other, and operate like a pair of scissors. By this process flour is made ready for bolting by one grinding.
In high milling process, grooved stones are employed, but are kept so far apart that at first the wheat is only bruised, and a series of grindings and siftings is necessary. This process is applicable only to the hardest wheats, and is partially supplanted by roller-milling.
In roller-milling, wheat is subjected to action of a pair of steel or chilled-iron horizontal rollers, having toothed surfaces. They revolve in opposite directions, at different rates of speed, and have a cutting action.
Porcelain rollers, with rough surfaces, are sometimes employed. In this system, grinding is accomplished by cutting rather than crushing.
“The disintegrator consists of a pair of circular metal disks, set face to face, studded with circles of projecting bars so arranged that circles of bars on one disk alternate with those of the other. The disks are mounted on the same centre, and so closely set to one another that projecting bars of one disk come quite close to plane surface of the other. They are enclosed within an external casing. The disks are caused to rotate in opposite directions with great rapidity, and the grain is almost instantaneously reduced to a powder.”
After grinding comes bolting, by which process the different grades of flour are obtained. The ground wheat is placed in octagonal cylinders (covered with silk or linen bolting-cloth of different degrees of fineness), which are allowed to rotate, thus forcing the wheat through. The flour from first siftings contains the largest percentage of gluten.
Flour is branded under different names to suit manufacturer or dealer. In consequence, the same wheat, milled by the same process, makes flour which is sold under different names.
In buying flour, whether bread or pastry, select the best kept by your grocer. Some of the well-known brands of bread flour are King Arthur, Swan’s Down, Bridal Veil, Columbia, Washburn’s Extra, and Pillbury’s Best; of pastry, Best St. Louis. Bread flour should be used in all cases where yeast is called for, with few exceptions; in other cases, pastry flour. The difference between bread and pastry flour may be readily determined. Take bread flour in the hand, close hand tightly, then open, and flour will not keep in shape; if allowed to pass through fingers it will feel slightly granular. Take pastry flour in the hand, close hand tightly, open, and flour will be in shape, having impression of the lines of the hand, and feeling soft and velvety to touch. Flour should always be sifted before measuring.
Entire wheat flour differs from ordinary flour inasmuch as it contains all the gluten found in wheat, the outer husk of kernels only being removed, the remainder ground to different degrees of fineness and left unbolted. Such flours are sold by the different health food companies, who have agencies in the large cities. Franklin Mills, Old Grist Mill, and Health Food flours are included in this class.