52 



Strength in Wheaten Flour 



Shutt, F. T. — "The Influence of Environment on the Composi- 

 tion of Wheat" ("J. Soc. Chem. Ind.," 1909, 28, 336-338). 



Snyder. — ("Minnesota Expt. Station Bulletin," 1904). 



Whymper, R. — " Microscopic Study of Changes occurring- in 

 Starch Granules during Germination of Wheat " (" Int. Congress 

 of Applied Chemistry," London, 1909). 



Wood, T. B.— "The Chemistry of Strength of Wheat Flour" 

 ("J. Agric. Sci.," 1907, 2, 139-161; 267-277). 



Wood, T. B., and W. B. Hardy.— " Electrolytes and Colloids; 

 the Physical State of Gluten" (" Proc. Roy. Soc," 1909, 1381, 



3 8 -43). __________ 



IX. 



AN ANALYSIS OF THE FACTORS CONTRIBUTING TO 

 STRENGTH IN WHEATEN FLOUR. 



By W. B. Hardy, F.R.S. 



Reduced to the simplest terms, the physical properties of dough 

 depend upon the protein complex gluten, starch grains, and 

 water. The greater the water-absorbing power of the gluten, 

 that is the greater its water content, the less will be its tenacity 

 and, within limit, the greater its ductility. 



Colloid bodies such as moist gluten have a sponge structure, 

 and when solid particles are present the bars of the sponge-work 

 may be seen under the microscope to spring from them. Thus 

 solid particles may enter intimately into the framework, and by 

 their size and number modify the thickness and length of the 

 bars and the size of the interspaces. Rubber loaded with solid 

 particles has elastic properties widely different from those of 

 rubber free from particles, and moist gluten loaded with starch 

 grains differs from gluten washed approximately free from them. 

 It is less like elastic, more like putty, in its mechanical properties 

 - — the solid grains of starch act as though they enormously 

 increased the internal friction. 



There has, so far as I know, been no exact work upon the 

 influence of the size and number of the starch grains upon the 

 mechanical properties of dough ; in the absence of such informa- 

 tion it is idle to pursue the point further. This may, however, 

 be said : judging by what is known of the influence of embedded 

 small particles in other cases, the power of the dough to retain 

 its shape may be due in some cases primarily to the nature and 

 number of the starch grains. Whatever the influence of the 

 starch grains may be, they operate as passive agents ; the active 

 mechanical properties of dough, its tenacity and ductility, are 

 due to the protein complex gluten. This is the labile elastic 

 cement of the structure. 



Now gluten, even though it be prepared from the best Fife 

 flour, has of itself neither ductility nor tenacity. In presence of 



