FREE INSTITUTE OF SCIENCE 



93 



THE CHEMISTRY OF BREAD-MAKING 



which amounts to a small fraction of one per cent., as a rule, is due to lactic 

 acid with small traces of acetic acid (about ninety-five per cent, lactic and five 

 per cent, acetic); sometimes, but rarely, butyric acid is present if improper 

 fermentations have set in. 



4. Leavening the Dough by the Action of Bacteria. — For many years one of 

 the home methods of making leavened bread practised in many localities was 

 the "salt-rising" process, as it was usually called. In this method of bread- 

 making wheat flour and corn meal are mixed with hot milk and salt and set in 

 a warm place. In the course of a few hours fermentation sets in and the whole 

 mass becomes porous. In this condition it is mixed with flour to make a 

 dough, as in the slack sponge process of wheat-bread making. This dough, 

 when set aside in a warm place, undergoes a fermentation similar in many re- 

 spects to that produced by yeast. The underlying principles of this method 

 were not clearly understood until very recently. Even as late as 1898 the 

 United States Department of Agriculture, in an official publication, stated, 

 regarding this process, that "the fermentation of dough may be secured by 

 enzyms naturally present in flour." 



It has been shown by research work on the subject that the above changes 

 are due to bacteria of certain types. Pure cultures of these bacteria are now 

 furnished for use on the large scale for this method of bread-making. The 

 chemical reactions have not yet been studied sufficiently to be intelKgently 

 described. It is known that no alcohol is produced during the decomposition 

 changes and that carbon dioxid and hydrogen are the gases to which the 

 leavening effect is due. The bacteria act upon the sugar of the flour and upon 

 the sugar and the casein of the milk used in the initial stages of the process. 



Chemical Changes During Baking. — The temperature at which bread is 

 baked ranges from 180° C. (355° F.) to 220° C. (425° F.). The changes pro- 

 duced by the heat are not as numerous nor as marked as might be supposed. 

 The major portion of the starch, which is the most abundant constituent of 

 bread, is not affected chemically, but is altered physically by the combined 

 effects of heat and moisture, so that the individual granules are greatly dis- 

 tended or entirely ruptured. A small proportion of soluble starch is produced 

 by the heat in the interior of the loaf, while the exterior of the loaf has had a 

 large proportion of the starch converted into the isomeric substance dextrin, 

 CeHioOb, from the same cause. It is this constituent which gives the sweet 

 taste to the crust. After baking, the principal change which occurs is the 



