ELEMENTARY PHYSIOLOGICAL CHEMISTRY 213 



Grains poor in gluten-forming globulins 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. 



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

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

 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 rezume of the process : 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 ferment- 

 ing 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 s sour acids which 

 develop in leaven are present. Besides the yeast, an unorganised fer- 

 ment called diastase, originally present in the flour, becomes active and 



