The New International Encyclopædia/Flour
FLOUR (formerly a variant of flower, q.v., for etymology). The ground and bolted substance of wheat. The name is also applied to other grains when ground, as rye flour, buckwheat flour; but if the grain from which the flour is made is not specified, the unqualified term, both in common and commercial usage, means wheat flour. The comparative importance of its production is shown from the fact that of the total cereal products milled in the United States in 1900, 62 per cent. were from wheat. Corn-meal, of which 13 per cent. of the total product consisted, ranked next, the remaining 25 per cent. being divided among the other cereals. That the use of wheat flour to the exclusion of all the other grains is not due to its higher nutritive qualities is shown from the accompanying analysis:
|Maize||Rye|| Carolina |
As pointed out in the article Bread, the universal use of wheat flour for bread is due to the presence in the kernel of crude gluten, containing gliadin, a highly tenacious body, which is not present in the same form in other cereal flours. This adhesive or sticky quality of wheat flour enables it to retain the carbonic-acid gas inserted in the form of yeast or baking-powder, and thus produces ‘lightness’ in the bread. For the same reason other flours are used most successfully when combined with wheat flour. In fact, the other flours are rarely used alone for bread, except rye flour, from which the ‘black bread’ of Germany and northern Europe is made. This is a dark-colored, heavy, and sourish bread, very slow to dry, which is itself improved by combining wheat with the rye flour.
Historical Development of Milling Processes. Long before the dawn of history cereals formed an important article of food for the human race, especially for that portion of it inhabiting temperate climates. At first these grains were used in the wild state, without grinding or cooking. But agriculture was one of the earliest arts of civilization to be developed, and the cereals the first of the agricultural products to receive cultivation. It must have been discovered very early that both in ease of mastication and in flavor grain is much improved by grinding, so that the first milling processes came soon after the cultivation of the soil. At first a mere breaking up into coarse fragments by means of a mortar and pestle, or its substitute, was all that was attempted. This primitive form of milling, whose adoption constituted the first step in the art, still survives among certain peoples of rude civilization. The second step in the development of milling processes was taken when for the mortar and pestle were substituted two roughened grinding surfaces, placed close together, between which the grain was reduced to powder. This use of the upper and nether millstone for grinding grain also dates back to prehistoric times. An improvement over this simple device is the quern, or hand-mill, still used among semi-civilized peoples. In the quern the upper stone is pierced and turned on a pin on the nether stone; the upper stone is grasped by a handle consisting of a stick thrust into its edge. The use of animal and then of water power to turn the millstones came much later. The first successful steam flour-mill was erected in London in 1784. The use of millstones for grinding flour was universal until the close of the eighteenth 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 kernels are softer and more starchy, is more easily separated from the husk than the spring wheat, whose kernel is much harder and much richer in gluten. The richer the wheat, the more difficult becomes the process of separating it from the husk, because the gluten is itself the cause of the toughness. Hence winter wheat produces a much whiter flour than spring wheat when both are ground by millstones. But in order to produce a white flour from either kind of wheat a large portion of the middlings, being inseparable from the bran, is lost. Hence the problem how to save and purify the middlings is a vital one with millers. While the old process aimed to avoid middlings as entailing loss of flour, the new process seeks to produce middlings, because out of the middlings comes the high-grade flour and the gluten which gives flour its rising power is saved.
The machines called ‘middlings purifiers,’ for winnowing the wheat between the successive grindings, are of two general types, the gravity and sieve purifiers. In the gravity purifiers, which are used for the larger-sized grains, the middlings pass in a thin stream through a current of air produced by a revolving fan, and so regulated that the bran is blown away while the wheat, being heavier, drops down into a receptacle. The sieve is an oscillating strainer of gauze, through which a current of air passes outward, carrying off the bran, while the wheat passes through the sieve. Many of the middlings purifiers in use are quite complicated in their structure, but the general principles upon which they operate are as described above.
Grades of Flour. Three grades of process flour are on the market: High-grade patent flour, baker's flour, and low-grade flour. One hundred pounds of good wheat produces about 76 pounds of all grades, and of these 72 to 76 per cent. is high grade and 18 to 22 per cent. baker's, the remainder being low grade. The accompanying table, compiled from figures published in the Year Book of the Department of Agriculture (1897), shows the comparative food values contained in different grades of flour, while the ash, fibre, and water represent waste. The four flours given in the table are the high-grade patent flour, baker's flour, common market flour, and flour of small mills, the samples being procured by regular purchase in the markets of Washington:
Food Values of Different Grades of Flour
| Flour |
Various attempts have been made from time to time to produce a flour which should contain all the nutritive elements of the wheat, and still be palatable and digestible. Perhaps the earliest and best-known of these is graham flour, so called introduced by Dr. Graham. This contains not only all the wheat, but the husk as well. It is coarse in texture, and, on account of the large amount of indigestible husk, irritating to some stomachs. Later the so-called whole-wheat or entire-wheat flours were brought upon the market, a much finer product, with more or less of the husk excluded. Gluten flours, from which the starch has been almost entirely excluded, have also been manufactured, and are valuable in certain forms of dyspepsia, where there is an inability to digest starch.
Self-Raising Flour. This is simply a flour into which has been mixed some chemical leavening agent, such as an ordinary baking-powder, or its constituents. This is possible, because bicarbonate of soda and tartaric acid, for instance, do not combine to produce carbonic-acid gas except in the presence of moisture. In the Year Book of the Department of Agriculture for 1897 analyses are given of a typical self-raising flour and of the common brands of flour, as offered for sale in open market at Washington. From these the following comparative table has been prepared:
|Proteids (factor 6.25)||10.10||10.50||12.30|
Now, as the ash represents waste, the significant fact in this table is the relatively large amount of ash in the prepared flour, there being an excess of 3.5 per cent.
Flour Manufacture in the United States. In Colonial days large quantities of wheat were raised and converted into flour in America; but with the Hessian soldiers of the Revolution was imported the Hessian fly, a scourge which literally drove the production of wheat across the Alleghanies. Since that time the centre of wheat and flour production has steadily moved to the Northwest. In 1815 a steam flour-mill, having a capacity of 700 barrels per week, was built at Cincinnati. The first merchant mill in Minneapolis was erected in 1854. During the last half-century the importance of the latter city as a milling centre has increased so rapidly that it now ranks first in the world as a producer of flour. With the new process of flour manufacture came the era of the big flour-mill. This was due partly to the fact that the machinery involved is too complicated and expensive for the small manufacturer, and partly because this change is simply in line with modern industrial development. In the bulletin on flouring and grist-mill products of the U. S. census of 1900 a distinction is made between merchant and customs mills, and from the statistics given it is evident that milling on a small scale is still a flourishing industry. Customs mills are defined in this report as mills grinding wheat, corn, and other grain furnished from farms in the neighborhood, and are usually denominated grist-mills. Merchant mills are large manufacturing establishments supplying the home market, and exporting flour to the principal foreign countries. In mere numbers the customs or exchange mills constitute 59 per cent. of the total number of milling establishments. The largest number of small mills was found in Pennsylvania, and of mills of the greatest capacity in Minnesota, The total number of flour and grist-mills grinding wheat was 13,188, of which 1655 belong to the class producing less than 100 barrels per annum. The growth of the milling industry in general during the last half-century is shown by the following statistics: In 1850 there were 11,891 establishments in the United States engaged in milling cereal products; in 1900 there were 25,258 such establishments, in 1850 the capital thus invested amounted to $54,415,581, and the value of the annual product to $136,056,736; in 1900 the capital invested amounted to $218,714,104, and the annual product to $560,719,063. Of this total product, 18,699,194 barrels of wheat flour, valued at $67,760,886, were exported.
SIDE SECTION OF A MODERN AMERICAN FLOUR MILL
(From plans furnished by the Nordyke and Marmon Company, Indianapolis, Ind.)
END SECTION OF A MODERN AMERICAN FLOUR MILL
(From Plans furnished by the Nordyke and Marmon Company, Indianapolis, Ind.)
Bibliography. The history of flour manufacture in the United States is given in One Hundred Years of American Commerce (New York, 1895). For statistics, together with considerable historical and descriptive matter, consult the United States Census for 1900, vol. ix, “Manufactures,” part iii. A complete description of the mechanical process of milling may be found in the “Report of the Statistics of Agriculture,” U. S. Census of 1880, vol. iii. The chemical composition of the various cereals used as food and of the products evolved by milling, and of the final products formed therefrom by baking and other methods of preparation, are given in part ix., Bulletin 13, “Cereals and Cereal Products,” of the Bureau of Chemistry of the United States Department of Agriculture.
- And fibre.