MILLING 161 



The middlings from the various breaks, after 

 going through the purifier, are further reduced by 

 being passed between several sets of smooth rolls. 

 The flour product of each reduction is then bolted. 

 This consists of sifting the flour through silk 

 screens of closer and closer texture, until a very 

 fine-grained flour is the product. 



Bleaching the Flour.- -The flour from some 

 wheat as it comes from the bolters is dark. White- 

 ness in flour is as much desired as is whiteness in 

 sugar or yellowness in butter. The demand by 

 buyers for a white flour has brought about the 

 bleaching process. Under the old method the flour 

 had to be stored for about three months in order to 

 whiten it. This was a natural bleaching process, 

 but it was very slow. Flour that was to be sent 

 abroad could be bleached in this way, as it would 

 whiten during the period of transportation, but a 

 method which required a shorter time was deemed 

 a necessity. 



The Alsop process, invented by Alsop in 1904, 

 is the one now generally used in the big mills. In 

 England it is known as the Andrews method. Its 

 advantage is that it prepares the flour for imme- 

 diate use and thus saves the expense of storing. 

 The treatment consists of subjecting the flour to 

 the action of nitrogen peroxide, a gas which is 

 made up of nitrogen and oxygen chemically united. 

 As the flour in a thin stream is emptied into the 



