176 X)r. Colquhouns Essd^iv^^ {SkptJ 



poses at least great part of the lactic acid^ and resolves it also 

 LDto the acetic. 



This theory seems to explain satisfactorily all the leading 



Ehaenomena accompanying the progress of fermentation in 

 aker's dough, and also to account for some of its results as 

 appearing in the progress of baking, which do not admit easily 

 of any other solution. Thus it appears that the subject of the 

 bread-fermentation in common practice, is, in every case, exclu- 

 sively the saccharine principle of flour. That the kind of 

 panary fermentation is by no means peculiar, but always in the 

 first instance the common vinous or alcoholic fermentation of 

 sugar, accompanied as usual by a copious evolution of carbonic 

 acid gas. That after this has gone on for a certain length of 

 time, a second process of spontaneous decomposition com- 

 mences ; the alcoholic principle lately extricated ferments, and 

 is resolved into acetic acid, at the same time that, in all probabi- 

 lity, a considerable portion of lactic and acetic acid is generated 

 at the expense of certain other ingredients of the flour, which, 

 at the commencement of the fermentative pix)cess, had remained 

 quiescent ; and it seems not improbable that a contemporaneous 

 formation of ammonia in the dough takes place to a certain 

 extent. It has been already stated to be an ascertained point, 

 that the lactic acid is frequently produced by the spontaneous 

 decomposition of a vegetable substance, when exposed in a state 

 of humidity to a moderately-warm temperature; and besides, 

 the existence of this acid seems proved by the change pro- 

 duced by baking sour dough, in regard to the organs by which 

 its acidity is perceptible before and after baking. 



But if that acescence which always injures so greatly the 

 quality of the bread in which it occurs, be truly the result of a 

 second process of decomposition, the materials for which are 

 only furnished after the first process has been carried on to a 

 considerable extent, it becomes obviously the secret of the 

 baker's art to interfere and check the progress of fermentation 

 in dough, while yet it is confined to the simple process of 

 saccharine decomposition, and before the resolution into acetic 

 acid of the alcoholic principle thereby evolved begins. Indeed 

 that may be defined to be good bread, in which the fermentative 

 process has been so regulated and checked; the art of doing 

 which cannot of course be otherwise acquired than by expe- 

 rience. But there are other methods, and these extremely 

 simple and effectual, for enabling tlie baker to adopt measures 

 either to prevent or to correct the evil of supervening acidity, 

 and to them our attention will now be shortly turned, before 

 concluding this general view of the several operations and 

 changes in the most common system of baking bread. 



We have already spoken of the nature of the process which 

 generates acidity in fermenting doughs, an inconvenience too 



