178 COLLOIDS IN BIOLOGY AND MEDICINE 



Ultimately we obtain a framework of coagulated gluten whose 

 pores are filled with shattered starch grains. 



The crust, which does not swell much, acts as a protection 

 both against the absorption of water and its loss from the interior. 

 A good bread should contain from 35 to 45 per cent of water. 

 Upon keeping, it loses about 1 per cent daily until the loss reaches 

 15 per cent. After that, the water content is dependent on the 

 humidity of the atmosphere; this corresponds to the behavior of an 

 elastic gel. It is interesting to note that the salt content plays a 

 role in the condition of swelling, because unsalted bread dries much 

 more readily than salted bread. 



There is a widespread error that stale bread has lost water and is 

 dessicated. This is not true; the crumbling consistence of stale 

 bread is due to a shifting of the water within the loaf; the starch 

 grains transfer water to the albuminous framework. J. R. KATZ 

 studied this problem and found that bread kept fresh longer at 50 to 

 100 C. as well as below 10 (best in a current of air), in other words, 

 there is a balance of swelling in starch and gluten which corresponds 

 to that of fresh bread. At from 0-25 C. stale bread is the stable 

 form. Staling is a particularly reversible process; dry rolls are made 

 fresh by heating them. This is an old expedient frequently employed . 

 The results of KATZ' research on keeping bread fresh at low tem- 

 peratures deserves the attention of the trade. 



The digestibility and available food value of bread depend par- 

 ticularly upon its " dispersibility " and swelling capacity. 



A perfect wheat bread may be utilized to the extent of 94 per cent 

 a rye bread to 90 per cent. For this purpose, the flour used must 

 be as fine as possible, otherwise the utilization is imperfect. It must 

 also be properly swollen up; fresh bread which is too wet is digestible 

 with difficulty. It packs together and the changes induced by the 

 incorporation with the saliva and other digestive juices are differ- 

 ent from those with old or dry bread. Most difficult to absorb are 

 the proteins (55 to 85 per cent). The great heat (in the inner parts 

 amounting to 110), acting in the presence of a small quantity of 

 water, produces a coagulation which greatly reduces their swelling 

 capacity. 



The grain shortage during the war caused the attempt to make 

 bread from potatoes. Potato flour yields a heavy, indigestible mass 

 when heated in the way usual for ordinary flour. Different attempts 

 were made to overcome this. According to A. FORNET, the Ex- 

 perimental Station for the Utilization of Grain mixes in an unknown 

 gluten substitute. WILHELM OSTWALD recommended blood or 

 casein dissolved in ammonium carbonate as a substitute for gluten. 



