PHYSIOLOGICAL CHEMISTRY 365 



The gluten is formed from two proteins in the flour, gliadiri (a protein 

 soluble in 70 to 80 % alcohol) and glutenin (soluble in alkali). It is to 

 the gliadin portion that gluten owes its viscidity; grains poor in 

 gliadin do not form dough when mixed with water, e.g. rice, oats, etc. 



Good flour does not contain sugar, and if that be present it shows 

 that a certain amount of germination has occurred. 



Wlwle flour is obtained by crushing the entire grain minus the husk 

 and outer portion of the bran. It contains somewhat more protein and 

 fat than does white flour and is accordingly more nutritious, but on 

 account of the admixture of bran which it contains, it is less digestible 

 and acts as a mild laxative on the intestine. 



BREAD AND BREAD MAKING. 



The gluten which is formed when water is added to flour cannot be 

 directly used as a food, for, on account of its soddenness, it is impervious 

 to the digestive juices, and cannot therefore be digested. Before it 

 can be digested it must be aerated, i.e. rendered porous, and in this 

 state it forms bread. The agency employed to aerate the bread is 

 carbon dioxide gas, which is generated in the mass of gluten or " dough" 

 by the action of the yeast plant on sugar. 



The following is a brief account of the process of bread making : The first 

 stage in the process consists in preparing an active culture of the yeast plant. 

 This was originally done by allowing dough to stand exposed to the air, when 

 some of the yeast cells, which appear to be omnipresent in the atmosphere, 

 settled on it, and grew and multiplied there until a fermenting mass or "leaven" 

 was obtained. Unfortunately for this process, however, the atmosphere contains 

 other bacteria which also settle on the dough, and by their growth lead to the 

 production of organic acids, in consequence of which the mass became very sour. 

 To make bread a little of the leaven was added to fresh dough, in which it grew 

 and multiplied until the whole was leavened, the aerated mass being then heated 

 so as to stop the fermentation. Such bread is very sour, and although the 

 process is still carried out in some parts of Germany, it is almost obsolete. 



In the modern process the leaven gives way to the so-called ferment, which is 

 produced by adding some pure yeast obtained from the brewery to a culture 

 medium consisting of a mixture of mashed potatoes and flour, the culture being 

 kept in a warm place for about five hours. By this time the mass is swarming 

 with young actively-growing yeast cells, and, provided that contamination with 

 bacteria has been prevented, none of the sour acids which develop in leaven are 

 present. Besides the yeast, an unorganised ferment called diastase, originally 

 present in the flour, becomes active and hydrolyses some of the starch of the flour 

 into sugar. The yeast cells then act on this to produce alcohol and carbonic acid 

 gas, so that a fermenting mass is obtained. More flour is now added to this, and 

 the process allowed to proceed five or six hours longer, until the developed gas 

 causes the top to burst, after which the remainder of the flour is added. The 

 mass is now called dough. It is thoroughly mixed by machinery, and allowed to 



