1826.] on the Art of Baking Bnad. 175 



ginous principles may likewise pass into a state of acescence, 

 and so contribute towards the activity of the acetous fermentei* 



tion. ■ ■■■' ■-■: -iJ-KKj'r; 



It has been universally taken for granted among authorsy ^<f 

 the acid thus developed in dough is exclusively the acetic. And 

 when we reflect on the facility and frequency with which this 

 principle is formed during the decomposition of organized mat- 

 ter, and on the abundance of materials which are in this instance 

 afforded for its production, we must admit that it generally 

 constitutes the chief principle of acidity in sour dough. 

 Perhaps, however, it is rarely the sole cause of this acidity ; for 

 there seem good grounds to conclude that another acid ofi!»t 

 more fixed nature, most probably the lactic, becomes not unfrea- 

 quently associated with it ; particularly when the fermentation 

 of the dough has been more tardy than usual, in consequence 

 either of the imperfection of the yeast, or of the original bad 

 quality of the flour. It has been proved, of late, by the experiit 

 ments of Braconnot, Vogel, and others, that this acid is gene*^ ^ 

 rated with much readiness, and to a considerable amount, during 

 the spontaneous decomposition of a great variety of vegetable 

 substances when in a state of humidity. And the presence of 

 lactic acid would account for a remarkable circumstance coii^ 

 nected with the acescence of dough, of which it is difficult to 

 suggest any other explanation, and which occurs in a most 

 striking manner in those cases, where fermentation has been 

 allowed to run on to great excess. This is the fact, that the- 

 acidity of unbaked dough in this condition is greatly more per- 

 ceptible to the palate than to the olfactory nerves, while the 

 sourness of the same piece of bread after coming out of the 

 oven, is, on the contrary, much more offensive to the smell than 

 to the taste. Now this is precisely what might be expected to 

 happen, if we suppose that lactic acid contributes, in conjuno-» 

 tion with the acetic, to produce the acescence of sour dough. 

 At the ordinary temperature of a bake-house, the former acid, 

 although very perceptible in the mouth, is not distinguishable 

 by the nostrils; but as it is easily decomposed by heat, no 

 sooner is it exposed to the high temperature of the oven, than, 

 as has been proved by the experiments of Berzelius, it is, in a 

 great measure, resolved into the acetic acid, and so becomes 

 more palpable to the sense of smell, and less so to that of taste. 



It would appear, therefore, from what has just been stated, to- 

 be a pretty- well-established point, that in acescent dough, 

 a second decomposition has always come into play ; that this is 

 probably at first of a mixed character, and consists partly of the 

 resolution into acetic acid, of the alcoholic principle previously 

 developed by the saccharine fermentation, and partly of the 

 formation of lactic acid ; while the heat of the oven, which 

 checks the saccharine fermentation, at the same time decom- 



