Scientific Lectui?es. 105 



Flour axd Brax — Gluten and Starch. 



"When this grain is crushed as between the stones of a mill there 

 results a reddish gray powder, the whole meal, which is made up of 

 scales and dust. These two products may be separated by bolting, 

 giving on the one hand bran, divided in England into several grades 

 of toppings, pollard, etc., and in this country into eonnell, shorts, 

 spouts, coarse and fine middlings, etc., and on the other hand, fine 

 flour. If the fine flonr be intimately mixed with a small quantity of 

 water it constitutes the elastic, somewhat tenacious, substance, with 

 which we are familiar in the form of dough. If this dough be 

 kneaded in a gentle stream of water, the water will become milky, and 

 if the water be received in a jar there will settle out a white powder. 

 If the washing be continued at length, the water will cease to be 

 milky and we shall have remaining a tough, higlily elastic body, 

 somewhat like India rubber, known as gluten. The white powder 

 that has been separated is starch. The gluten has been separated by 

 chemists into several bodies vvdiich have very nearly the same consti- 

 tution, but which differ from each other somewhat in properties. 

 These are albumen, mucin, gliadine, conceived to be the particularly 

 elastic constituent, and cerealine, to which Mege Mouries ascribed a 

 special susceptibility to fermentation. For convenience we may 

 regard them as various forms of more or less perfect gluten. All of 

 them contain nitrogen and phosplioric acid, and beside carbon, hydro- 

 gen and oxygen. Starch contains only carbon, hydrogen, and 

 oxygen. Beside the gluten and starch, the wheat contains a little 

 sugar and oil. 



Fermentation — Different Kinds. 

 The chemical properties of these two bodies — gluten and starch — • 

 are in the highest degree unlike. An acid like vinegar or lactic acid 

 (the acid of sour milk), will deprive the gluten of its elasticity, and 

 in time convert it into a fluid. Left to itself, with a small, quantity 

 of water, the gluten goes over spontaneously into a variety of less 

 complex bodies, yielding carbonic acid, phosphate, lactate and acetate 

 of ammonia, and some less familiar bodies, leucin and tyrosin, and 

 some volatile sulphur compounds. In time, indeed, it will become a 

 perfectly transparent fluid. Starch by itself would not change, but in 

 contact with the gluten, as in flour, it would, under certain conditions 

 of temperature and moisture, yield dextrine (gum) which would 

 become sugar, and the sugar alcohol and carbonic acid, and the 



