274 THE BOOK OF WHEAT 



will yield the results which he desires in the final milling. 

 Heating the wheat to a certain temperature is a part of the 

 tempering process, and moisture in some form is always applied. 

 This may be accomplished by one or more applications of water, 

 of steam, or of both water and steam. 



MILLING PROPER. The wheat is passed between corrugated 

 steel rolls, each of which moves at a different speed from its 

 mate. The berry is not crushed, but ruptured and flattened 

 out, so that its interior can be separated from the bran coats 

 in the largest pieces possible. As much of the interior as is 

 thus separated from the bran coats is sifted out, and the resi- 

 due is again passed through steel rolls so that more of the 

 interior may be separated. This is what is meant by gradual 

 reduction. 



The interior of the berry which has been separated from the 

 branny portion is known as "middlings." This material is 

 now passed through the middlings purifier, which removes any 

 particles of bran that may be present, the cellulose structural 

 material of the interior of the berry, and the germ of the grain. 

 The latter would give the flour a yellow appearance, and im- 

 pair its keeping qualities. After the middlings have been puri- 

 fied, they are reground, and again purified. These processes are 

 repeated until the material is of such fineness that it will pass 

 through the finest silk bolting cloth. The material is tested at 

 every stage of the process, and finally the finished flour is again 

 tested before it is shipped to the trade. An expert can deter- 

 mine its quality largely by feel and color. Only the largest mills 

 have facilities for making chemical tests. The smaller millers 

 frequently have their products tested at chemical laboratories. 



The Bleaching of Flour is a process of recent origin, and 

 there has been considerable controversy as to its merits. The 

 most common method employed is to pass air through an elec- 

 tric discharge of high voltage and low amperage. This results 

 in the formation of oxide of nitrogen. The treated air is piped 

 to an agitator or spraying machine, through which the flour is 

 passing in a thin running stream. The latter operation requires 

 from 7 to 10 seconds, and during this time the flour is aged and 

 whitened. It is claimed that the only effect upon the flour is 

 the decolorization of its oil. Bleaching gives whiteness only, 

 and it does not enable the miller to increase the amount of Jlour, 



