Strength in Wheaten Flour. 



55 



curve gives the concentration of salt and acid needed just to 

 preserve cohesion. It will be seen that as the concentration of 

 acid is increasing, the concentration of salt needed to maintain 

 cohesion rises to a maximum and thence falls until a point is 

 reached where the acid alone is sufficient. The curve encloses 

 an area of no cohesion, while outside it is a region in which acid 

 and salt maintain cohesion. 



Neither of these areas represents uniform states; as is charac- 

 teristic of colloidal matter, they are areas of continuous changes. 

 The curve which limits them is merely an arbitrary line which 

 marks the place at which cohesion is so far reduced that it no 

 longer suffices to maintain shape against the extraneous force 

 of gravity. Any line, starting within the area of no cohesion 

 and passing through it to the area of cohesion, traverses a system 

 which is continuously changing— namely, a colloidal solution 

 containing exceedingly fine particles of gluten which become con- 

 tinuously coarser until finally, at or near the intersection of the 

 curve, they run together into a coherent mass of gluten. Beyond 

 the curve the line, if it be inclined upwards, follows a system 

 in which still further separation of water and gluten is taking 

 place, the two becoming less and less miscible — the water-holding 

 power of the protein less and less, its tenacity growing, its duc- 

 tility diminishing. 



Electrolytes, therefore, do more than confer on gluten its 

 mechanical properties ; they determine also its power of holding 

 water. They also determine the water-holding power of any 

 other colloid matter present in the dough. 



Acids and alkalis destroy cohesion and disperse the particles 

 of gluten just as they produce and stabilise non-settling suspen- 

 sions in many types of colloidal solution — namely, by the develop- 

 ment of a difference of electric potential between the particles 

 and the water. The curve which connects the potential difference 

 with the concentration of acid has the same form as the curve 

 given in Fig. i. 



The foregoing analysis of the factors which control the physical 

 properties of gluten in moist dough lead us to a brief analysis of 

 the source of " strength " in flour. It must be borne in mind 

 that loaf-making includes two distinct operations, the making 

 and incubation of the dough and the fixation of the incubated 

 dough by heat. Every factor which contributes to the rising of 

 the dough — that is, to the size of the loaf — and to the power of 

 the dough to preserve its shape (saving only the vital activities 

 of the yeast plants) intervenes also in the fixation of the dough, 

 where it may undo what it has already done. Successful incuba- 

 tion depends upon : (i) The suitability of the dough for the active 

 growth and production of carbonic acid by the yeast plant, which 



