COMPOSITION OF WHEAT 41 



70. Gluten. — ^Wheat flour has the property in common only 

 with rye flour of forming a dough when mixed with water which 

 on leavening and baking produces a porous bread. This is due 

 to the gluten which imprisons the carbonic acid gas caused 

 by the fermentive action of the yeast. The gas expanding 

 during leavening and during baking causes the bread to become 

 porous. 



Gluten is a mixture of gliadin and glutenin and may be 

 obtained in a crude state from wheat meal or flour, by washing 

 the dough made by kneading the meal with water, which re 

 moves starch and other non-gluten compounds. Moist gluten 

 contains about sixty-six per cent of water and certain other 

 impurities which are in fairly constant proportions in different 

 samples. A good gluten has a light yellow color, is tenacious 

 and elastic, while poor gluten is dark in color, is sticky but not 

 elastic. 



" The gliadin ^^•^th \\ater forms a sticky medium, which by the presence of salts 

 is prevented from becoming ^Yholly soluble. This medium binds together the par- 

 ticles of flour, rendering the dough and gluten tough and coherent. The glutenin 

 imparts solidity to the gluten, evidently forming a nucleus to which the gliadin 

 adheres and from which it is consequently not washed away by water. Gliadin and 

 starch mixed in the proportion of i : 10 form a dough, but yield no gluten, the gliadin 

 being washed away with the starch. The flour freed from gliadin gives no gluten, 

 there being no binding material to hold the particles together so that they may be 

 brought into a coherent mass, 



" Soluble salts are also necessary in forming gluten, as in distilled water gliadin 

 is readily soluble. In water containing salts it forms a very viscid, semi-fluid mass, 

 which has great power to bind together the particles of flour. The mineral con- 

 stituents of the seeds are sufficient to accomplish this purpose, for gluten can be 

 obtained by \\-ashing a dough with distilled water." 



The amount and quality of gluten — especially the latter — is 

 what gives the fl.our its baking qualities. The quality of the 

 gluten is due in part at least to the proportion of gliadin and 

 glutenin. M. E. Fleurent states that the most favorable ratio of 

 glutenin to gliadin is twent}^-five of the former to sevent}^-five 

 of the latter. He gives analyses of two varieties which are in 

 the ratio of 23 : 77 and 30 : 70 respectively, and suggests that 



