USES OF CEREALS 547 



In 1878 a small roller mill was established in Minneapo- 

 lis, said to be the first complete roller mill in the United 

 States. At the close of 1877 there were 197 runs of stone 

 in the 21 Minneapolis mills. In a few years all plants 

 in Minneapolis and all the principal mills elsewhere in this 

 country were roller mills. 



591. The modern roller mill. Rolls cause a gradual 

 crushing and flaking of the kernel, instead of pulveriza- 

 tion, as with stone burrs, and thus allow a more perfect 

 separation of particles afterwards. They were at first 

 made of various materials, chiefly porcelain, but finally 

 the present perfectly formed steel rolls were adopted. 

 These rolls are usually 9 inches by 30 inches in size, and 

 are set in pairs in a cast-iron frame. They revolve toward 

 each other, from above, at a high speed but with a differ- 

 ential motion, that is, one roll revolves much faster than 

 the other. The rolls handling the first stock of wheat and 

 bran are corrugated with light furrows, slightly spiral in 

 direction. This coarse stock goes through 5 processes, 

 called " breaks," the corrugations -increasing in number 

 and diminishing in depth in each succeeding pair of rolls. 

 The finer stock called " sharps," from each break, not 

 used as flour, passes to smooth rolls called " crushes," 

 for further reduction. There are usually 6 or 8 con- 

 secutive reductions on smooth rolls. After each reduc- 

 tion the stock falls into a sifter which separates the mate- 

 rial, some to be re-ground, some to be sacked. There are 

 many kinds of sifters. Where the stock is coarse, angular, 

 and sharp, wire cloth is used; when it gets softer, silk 

 cloths are preferred. 



592. The milling process. The entire milling pro- 

 cess, in detail, is complicated, and entire books are written 

 on the subject. It consists of the following steps : - 



