184 USE OF YEAST. 



of lactic acid (377), and frequently vinegar likewise; 

 the latter is for the most part driven oiF in the sub- 

 sequent process of baking, but the former remains in 

 the bread. 



446. The baker usually commences by mixing 

 together in a suitable vessel a proper proportion of 

 yeast, warm water, common salt, and flour. The 

 salt is first of all dissolved in warm water, which is 

 then allowed to cool down to about 80° or 90°, after 

 which the yeast and then the flour is added. The 

 quantities taken vary slightly. The third part of a 

 sack of flour, a pailful of warm water, four or five 

 pounds of salt, and three or four pints of yeast, are 

 about the usual proportions. 



447. This mixture, which is called the sponge, is 

 worked up to the consistence of stiff batter, and then 

 left in a small trough for an hour or two, covered 

 over wath a cloth. During this time a tolerably 

 active fermentation is commenced, and as the mix- 

 ture is tenacious and viscid, the carbonic acid gene- 

 rated does not escape in bubbles, but is retained in 

 the dough, causing it to swell up to about twice its 

 original size. 



448. If the sponge is made too thin, the gas thus 

 generated will escape as fast as it is evolved ; if of the 

 right consistence, the whole of it will be retained. 

 If the fermentation is allowed to continue too long, 

 the sponge will become sour, and pass into the state 

 of leaven; the baker, however, does not permit this, 

 but when he judges that the fermentation has pro- 



