« AnteriorContinuar »
seems to have come into use in England about 1200. The first milling by steam was in England in 1784.
The earliest mills in the United States were operated byhorse power, and the toll was higher than at those where water
or wind power was used. The first mills of the Red river valley were operated by oxen, or by wind power. In 1870 there were 22 flour mills in South Carolina that were operated by horse
power. In Texas there were 50, and 17 more were driven byoxen, while wind furnished power for five. Many of the primitive forms of mills can still be found in operation in various parts of the world.
Modern Improvements and Processes.—In the first milling, the entire wheat went into the flour. There was no "bolting" or classification of the product by separating it into several grades. Usually not even the bran was separated. The first distinctively modern improvements were in the line of bolting the flour. The primary sieve was an extended bag which was shaken by machinery. Its first introduction was in the power mills at the beginning of the sixteenth century. A German miller seems to have the credit for bringing forth this reel as a flour-dressing device. It was the predecessor of all subsequent bolting apparatus and of all appliances for purifying and separating the various grades of flour.
The old Roman system of cylinder milling, which is similar in principle to an ordinary coffee mill, was developed in Hungary. Elsewhere the system known as "low milling" was more common. In this the grain was ground in one process between two crushers placed as near together as possible.
In the United States the flour making industry was early developed in Pennsylvania, and in connection with this was given the first patent to a citizen of the new world for an invention (1715). A Philadelphia woman invented the device, which was in its essential portion a series of mortars driven by mechanical power. In few industries has there been so much litigation and controversy as in the manufacture of machinery for milling. Many patents for machines with the same object in view were taken out almost simultaneously. In the invention of all kinds of milling machines, competition has been so brisk that it is difficult to determine questions of priority and relative efficiency. New York city and Philadelphia had good bolting facilities even before 1698, but such facilities did not become general until the beginning of the nineteenth century. Oliver Evans (Philadelphia, 1756-1819) invented the elevator, conveyor, drill, descender and hopper-bag, from which "dates the long period of so-called 'American' milling, which produced flour as economically and of as good a grade as that of foreign millers." There was little progress from the days of Evans until the introduction of the "new 'process about 1870. During the time of Evans, wheat was cleaned with rolling screens and blast fans. About the middle of the nineteenth century smutters were introduced, and a little later, separators, by means of which a more thorough system of wheat cleaning became established.
"Low" Milling.—Before 1850, the millstones in the United States were run at a comparatively low speed, and the grinding was slow. By this date the milling industry had assumed such commercial importance that it was necessary to increase the speed of the stones in order to get the work done. From 1850 to 1875, hard, low grinding was the rule, and the prime object was to make the largest possible percentage of flour at the first grinding. The change in process, due to greater speed, increased the output and improved its quality, "the outcome being a white, soft flour that met with favor in all he leading markets of the world where American winter wheat flours were handled." By this process, however, it was impossible to get the flour entirely free from contamination, and some of the bran always remained. There were two parts to this old process, reducing the wheat to flour by passing it through a run of stones, and bolting the resulting material in order to separate the flour from the bran and other undesirable parts of the kernel. The percentage of flour obtained by this single grinding depended on four things: (1) The dress of the millstone; (2) the face of grinding surface; (3) the balancing of upper or runner stones; and (4) the speed of the runner. As there was but one grinding, the making of middlings was avoided as much as possible. By this method of milling, some of the bran was pulverized so that it could not be separated from the flour. This gave the flour a darker color, and caused it to gather more moisture, which injured its keeping qualities, especially in moist or hot climates.
"High" Milling was the next step in advance. In this the speed of the stones was again decreased, and they were set far apart. This advance was made possible by the middlings purifier, which was not invented in the United States much prior to 1870, although its principle had long been known and applied in Europe. It was a machine for separating the dust, fluffy material, particles of bran, and the flour, from the middlings. It was now possible to make an excellent and pure flour from winter wheat, for the middlings thus purified were reground to superfine flour, which brought more per barrel than the best flour formerly in the market. As an indication of its superior grade it was called "patent" flour. The "new" process consisted of four parts, for purifying and regrinding the middlings were added to the "old" process. In the first operation the wheat was "granulated," not ground. These particles, technically known as "middlings," were run through the middlings purifier and then reground. Being of great advantage, the process was further developed by introducing more stages. The grain was now ground very coarsely and the endeavor was to make as little flour as possible at the first grind, and the largest possible amount of middlings.
Ever since the sixteenth century, when good flour began to be manufactured at the mills, and bolting had been introduced, winter wheat at all times and places had commanded a larger price than spring wheat. Spring wheat flour was usually of a dark and inferior grade, valued considerably below winter wheat flour. With the opening of the wheat regions of north central United States, however, spring wheat was produced in enormous quantities, even at the lower price which was paid for it, and there was great need of an improved process of milling which would produce a high grade of flour from spring wheat. Spring wheat proved to be better suited to grinding by the continually improving process of high milling than winter wheat, for being harder, it yielded a greater percentage of middlings. This had been its great disadvantage under the old processes of milling, where the purpose was ta get flour at the first grinding, and not middlings. All unpurified middlings are foul, and when reground they produced a low grade of flour. When the purifier remedied this difficulty, the best grade of flour was that made from the middlings, and almost at a single bound spring wheat took front rank as a flour producer. The winter wheat flour now became second grade instead of being the best.
Roller Milling.—The hard quality of spring wheat and the increasing number of " breaks," or stages in the milling process, necessitated new improvements. Rolls made of porcelain or of chilled iron were now devised to take the place of the timehonored millstone. The "new" process of high milling was first developed in the stone mills of Austria (1820-30). With an extension of principles, it became the Hungarian or gradual reduction process.1 Experiments with roller mills date from 1820 in Switzerland, and rolls were used in Hungary in 1874, although minor experiments date vaguely back to 1861. These Hungarian rolls were 7 inches long, 4Vk inches in diameter, and made from 180 to 200 revolutions per minute. The first complete roller mill was erected at Budapest, and for years the mills of this city produced the leading flour in the world's markets.
In the United States, the principles of the gradual reduction process were taken from Hungarian millwrights, and rolls were first used in 1878. A complete outfit of roller mill machinerywas brought to Minneapolis from Hungary, and Americanized. By 1880 rolls were rapidly coming into use, but it necessitated a change of machinery, and the change was stubbornly fought by the conservative old burr millers of this country. The spring wheat interests were large, however, and it seemed a useless fight. The thousands of small country millers held out longest, for the expense of the change bore most heavily upon them. The larger millers very successfully adopted the new process with all its intricate mechanical details. "Patent" flour had been fully recognized and established in commercial circles some time before 1876. Spring wheat brought 6 cents a bushel more in the market by 1882 than any other sort. Winter wheat formerly sold at from 5 to 30 cents a bushel more than spring wheat.
The Process of Milling wheat by the gradual reduction methods in the early eighties was quite complex. The grain was first passed through separators until it was perfectly free from foreign matter. It was then conveyed to ending stones, made of sandstone slightly harder than that, used for buildings, and having the shape and size of ordinary millstones. These removed the "whisker" and fuzz from the wheat, after which it went to the brush machine—always by machinery. Here the clinging dust was removed, and then it passed through a series of five break rollers, each successive pair being set a little nearer together than the last. The flour and middlings were 1 Smith, Hist, of Milling, Northwestern Miller, March 20. 1907.