1826.] on the Art of Baking Bread, 165 



is. done, the mass is said to be leavened, the dough thus added 

 while under fermentation being denominated leaven. The prac- 

 tice of leavening bread is familiar to every one, as havici^ been 

 known at the earliest periods of which we have any authentic 

 records. And, in point of fact, the same system, although 

 another process is superadded to it, forms a leading part of the 

 art of baking in the most civilized countries at the present day ; 

 for it is the almost invariable practice of the baker to induce 

 fermentation, not in the whole dough at once, but in a portion 

 only, with which the rest is afterwards leavened ; and thus it is 

 found, that the tendency to decomposition may be more rapidly 

 communicated to the entire bulk of that dough, which he intends 

 to convert into bread. 



It is no longer, however, by the addition of a Httle leaven that 

 the modern baker produces the commencement of his process of 

 decomposition ; for there is a particular substance which he has 

 discovered to possess the property of exciting fermentation in 

 dough with a still greater degree of rapidity. This is yeast, or 

 the frothy scum which is thrown up to the surface of a brewer's 

 vat, soon after the saccharine infusion has passed into a state of 

 active fermentation. Of this yeast, which is a very complex 

 and impure substance, chemists are not perfectly assured which 

 constituent it is that spreads decomposition among the dough ; 

 although there now seems to be little doubt that this is effected 

 by its glutinous ingredient, which has itself already begun to 

 pass into a state of decomposition. 



When the baker proceeds to the preparation of dough by 

 means of the yeast-fermentation, he at first takes, generally a 

 portion only, but sometimes the whole of the water, which it is 

 his intention to employ in making the required quantity of 

 dough. In this water, which varies in temperature, according 

 to circumstances, from 70° to 100°, there is dissolved a certain 

 portion of salt, the quantity of which, however, is always less 

 than that which will finally be required, in order to communicate 

 the necessary flavour to the bread : yeast is now mixed with the 

 water, and then a portion of flour is added, which is always less 

 than the quantity to be ultimately employed in forming the 

 finished dough. The mixture is next covered up, and set apart 

 in a warm situation ; within an hour after which, signs of com- 

 mencing decomposition make their appearance.* The sponge 

 begins to swell out and to heave up, evidently in consequence 

 of the generation of some internal elastic fluid, which in this 

 instance is always carbonic acid gas. If the sponge be of a 



* The substance thus placed apart is termed, in the language of the bake-house, the 

 sponge; its formation and abandonment to spontaneous decomposition is termed setting 

 the sponge ; and according to the relation which the amount of water in the sponge bears 

 to the whole quantity to be used in the dough, it is called quarter, half, or whoh 

 sponge. 



