WHEAT 115 



Later it became the custom to compel the slaves and crim- 

 inals to grind the flour and bake the bread. Still later 

 cattle furnished the motive power, and following the cattle- 

 mill came the water-mill, first used by the Greeks about 

 50 years b.c. Not until several hundred years later was 

 the windmill invented, and from the time when it first 

 came into use, great improvements were made in it over 

 the original type, and its use was rapidly extended. In 

 1784 we have the invention of the steam-mill in London. 

 In the year 1870 there was introduced in Minnesota a 

 machine which was to revolutionize the milling industry 

 in this country. The purifier, which was a machine for 

 separating middlings and flour, enabled the miller of the 

 Northwest to make acceptable flour from spring wheat, 

 which had hitherto been despised on account of its dark 

 color. During all this time the grinding surfaces of the 

 milling machines had been mill-stones, but in 1878 there 

 was introduced into this country the roller-mill, which 

 marked the greatest of all advances in the milling busi- 

 ness. 



102. Modern milling. — In modern milling there are 

 three fundamental processes, viz. cleaning, tempering, 

 and grinding. Each of these three main processes is com- 

 posed of several minor processes. The object of cleaning 

 is to remove all dust or dirt and foreign seeds. Special 

 machinery is used to rid the wheat of foreign seeds, after 

 which the grain is either dry-cleaned by being run through 

 scourers, or else it is washed and dried. The next process 

 is tempering the grain by the application of heat and mois- 

 ture, in the form of steam or water, or both. This toughens 

 the bran so that it will not crumble into fine particles, but 

 will break off in large pieces. Then comes the milling 

 proper, which is quite a complicated process and cannot 



