Rodney Norquist, age 12, of Casper, Wyo., for his question:
HOW IS FLOUR MADE?
Flour is the finely ground meal of grains of wheat. It is made by a process called milling. In the earliest milling process back in ancient times, the job was accomplished by a bowl shaped cavity called a mortar in which wheat was crushed by a rod called a pestle.
The earliest refined device for producing flour consisted of two roughened grinding surfaces, called millstones, between which grain was reduced to powder. Until the substitution of rollers for stones in the grinding process, the adoption of newly discovered sources of power constituted the only significant change in milling.
Present day milling processes start with the cleaning of kernels. Wheat arriving at a mill is generally mixed with such matter as straw, chaff, pebbles, earth and seeds of various kinds. Coarse and fine material is removed by passing the wheat through sieves, but seeds and other objects that approximate wheat grains in size must be extracted by special means.
Cylinders and disks that have perforations of various sizes not only separate remaining foreign particles but also segregate wheat kernels by size.
Next the wheat is scoured by being passed through an emery lined cylinder. Tempering, a process by which the moisture content is adjusted for easier separation of kernel from husk, is the last step in preparing the grain for grinding.
Because of the development of wheat varieties that do not require heavy friction provided by millstones, most grinding is done in roller mills. Corrugated rollers gradually reduce the wheat kernels to powder.
Initial rolling takes place in three to six stages, the last stage of which yields bran, middlings and flour. Finished flour consists almost entirely of endosperm, or nutritive tissue. Middlings are composed of fragments of endosperm, fragments of husk and husk fragments with adhering particles and endosperm. Bran is the broken husk of the grain.
Between each stage of rolling, the ground product is sifted, a process referred to by millers as bolting.
The finest grades of flour are obtained from the middlings that are left over from the bolting process. The flour is extracted by a process called purification. A purification machine is usually a sieve through which a stream of air is passed, separating the flour particles by passage through the meshes of the sieve and by floating in the air.
The grades of flour removed at successive stages of the milling process vary widely. For commercial purposes the milling grades are blended to produce standard grades or special commercial brands.
Most bread flour sold today is so called enriched flour, which consists of ordinary white flour with added vitamin B 1, niacin, riboflavin and iron, giving it the same vitamin content as whole flour.