106 TIiAxsACTJO^'S of the A31ERICAN Institute. 



alcohol acetic acid. Besides these there are sometimes produced 

 lactic acid, benzoic acid, formic acid, succinic acid, and glycerine. 

 These changes take place in tlie process which we know as fermen- 

 tation. "Wlien one of them, the change that yields carbonic acid 

 (whicli is a gas) predominates, the mass of moistened flour becomes 

 filled with bubbles. If the quantity of flour is large relatively to the 

 water with which it is mixed, tlie tenacity of the moistened flour — 

 the dough — will restrain the bubble, and so increase the volume of the 

 dough, Now if, in this inflated condition, the dough be placed in a 

 hot oven, so as to arch over the outside M'ith a stifle crust, and heat 

 the mass throughout, we shall have a loaf of raised bread. But it will 

 be very inferior, mainlj' for the reason that too many results of fermen- 

 tation have taken place. It will contain substances objectionable both 

 to taste and smell. We need only one of these results — the ])orons 

 structure. But we have in the dough in question the results of per- 

 haps half-a-dozen difierent kinds. Let me enumerate them. Chemists 

 have recognized the lactic fermentation, which yields more especially 

 lactic acid ; the mucous fermentation, yielding mucilage, or dextrine, 

 or gum ; the saccharine, which yields sugar ; the alcoholic, or vinous, 

 which yields alcohol and carbonic acid ; the acetic, yielding acetic 

 acid or vinegar; the butyric, yielding butyric acid ; and the putrid, 

 yielding offensive products. Besides these, there accompanies the 

 saccharine fermentation in bread what has been called an ammoniacal 

 fermentation, during which the dough is dark colored ; and the vinous 

 yields, beside alcohol and carbonic acid, certain agreeable essential 

 oils known as boquet or aroma. • Lactic acid abounds in putrid 

 fermentation. IS'ow, extraordinary as this must appear, that flour is 

 capable of these changes, there is one thing more extraordinary, if 

 l^ossible, in this connection ; and that is, that each type of fer- 

 mentation is attended by a special organic growth, its particular 

 ferment or yeast organism. In tlio acetic and putrid fermentations 

 there are animal organisms, while in the mucous, saccharine, and 

 alcoholic fermentations the organisms are vegetable. These organ- 

 isms feed on the ingredients of the flour to reproduce themselves, and 

 at the same time there are produced the chemical compounds due to 

 the particular kind of fermentation. Here is a diagram of the 

 ferment that attends tlie production of alcohol and carbonic acid, 

 prepared by tlie late Prof. Mitscherlich, of Berlin. It presents the 

 growtli of the yeast plant from hour to hour. (Diagram A.) 



I have said that each ferment plant reproduces itself. It can do 



