The advent of steam power greatly improved the efficiency of flour mills. In 1786, two 37-kW steam engines were connected to drive 20 stone mills (1.5 m in diameter) at the Albion grain mill in London (Fischer 1944), and for the next 100 years, grain was ground mainly in steam-driven querns. A flour mill that used steam-driven querns in the United States in the 1870s is shown in Figure 4.10. Soon afterward, roller mills began to replace the querns.
Both the querns and roller millers were found to be well suited for use in the “gradual reduction process” for making flour (see sidebar), which came to the fore in Hungary in the years from 1840 to 1870. At the time, rapid progress was being made in process engineering in nearby Austria and Germany, including advances in grinding technologies for the cement and ore industries. The intellectual environment of the industrial community has always been a definitive factor in innovation and progress, and industry was particularly progressive in central Europe during that time period. The Hungarian system was
THE GRADUAL REDUCTION PROCESS
Flour milling involves breaking the wheat grain to separate the endosperm from the bran (see Figure 4.11) and grinding the endosperm to flour. The problem is that much of the bran is not easily accessible because it is in the section of the grain that contains the germ, and cutting and peeling cannot remove the bran. Instead, fine grinding is necessary to liberate the bran for removal. The ancient methods of lightly breaking grains in a quern, sieving to free the bran, and grinding the remaining bran and endosperm again produced a fine flour that was edible but discolored and unattractive. Even though whiter flour could be made, more grinding and sieving was required, which drove up the price. Flour milling began to change in response to the growing demand for white flour in more prosperous countries.
By 1820, the continental wars had temporarily ended in Europe, and flour millers were able to invest time and money to improve the technology.
French engineers have introduced many original inventions, chiefly in the sphere
of transportation, cleaning of grain, and dressing of the product One of the
greatest inventions of the French of that time is the cleaner and separator, the most indispensable machine of the grain cleaning department. (Kozmin 1917)
Silk cloth proved to be more efficient for sieving than other materials, and millers used it to improve flour milling by operating querns in series with the first stones set well apart and the second stones closer together. The bran was captured from the ground products by sieving with silk—a system started late in the 18th century by the French miller Pigeaud. The combination of grinding in stages and using sieves to separate the ground products into size fractions became the basis for Hungary’s gradual reduction process. The prospect of producing large quantities of white flour came into view, and the subsequent inventions of purifiers and steel roller mills brought the picture into focus.
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FIGURE 4.11 Schematic view of a wheat grain
introduced in Minneapolis, Minnesota, in the early 1870s. In the years that followed, the gradual reduction process was quickly accepted by new flour-production facilities in the United States, where mechanical development of the roller mills continued.
W. D. Gray, superintendent of the milling machinery department of E. P. Allis & Company (the predecessor of Allis-Chalmers), built and installed roller mills in a flour — production plant in 1878. His mills were so good that they changed little for 50 years and caused the production of flour in the Minneapolis plant to increase from 2 million barrels in 1880 to 16 million in 1910: “It was the roller mill that wrested the milling crown from Budapest in Europe and St. Louis in [the] United States and gave it to Min — neapolis…and was responsible for an agricultural as well as an industrial evolution” (Peterson 1976). The agricultural revolution took place because roller mills were able to grind the hard and nutritious spring wheat more efficiently than querns.
CONCLUSION
The history of size reduction in the grain-milling industry parallels the growth in the development of processes, machinery, and technology, as more sources of energy became available to replace manual energy in driving the machinery. Although size — reduction techniques differ among the various industries, which use the process best suited to the particular needs of each, the pattern of growth in all the industries is the same. By the end of the 19th century, all the elements of modern-day grain milling were in place, and, by 1930, the gradual reduction system was in universal use. In the years that followed, the rolls were continually improved, with, for example, high-pressure hydraulic systems for roll support, better bearings, and special wear-resistant roll surfaces and liners.
Copyright © 2005 by the Society for Mining, Metallurgy, and Exploration.
All rights reserved. Electronic edition published 2009.