182 BREAD-MAKING. 



dough is converted into carbonic acid and spirit, by 

 the action of the yeast or ferment mixed with it ; the 

 carbonic acid thus evolved by dividing the dough, 

 and forming little holes and cavities throughout its 

 mass, renders the bread light and porous. 



439. There are two distinct objects to be attained 

 in the manufacture of bread, the one is the chemical 

 union and transformation of the starch and other 

 components of the grain, the other the formation of 

 a uniformly light, spongy, and easily digestible mass ; 

 the latter is merely a mechanical effect, but both 

 objects are effected by chemical means. 



440. The flour of wheat and other grains used in 

 bread-making, consists chiefly of starch, together 

 with a much smaller proportion of sugar, gum, and 

 azotized matters. These substances may be made to 

 undergo various changes, and these changes may be 

 brought about in many different ways; the most com- 

 mon and convenient, is to excite in them a state of 

 vinous or alcoholical fermentation. 



441. There are two distinct modes by which this is 

 effected, namely, the use of leaven and of yeast or 

 barm. Leaven is dough which has been kept till it 

 has turned sour; when this is mixed with a quantity 

 of fresh dough, it has the power of communicating to 

 the whole of the latter its own state of fermentation. 



442. A quantity of flour is kneaded up into dough 

 with a suitable quantity of water, and then left in a 

 warm place; it will soon become sour, and a greater 

 or less degree of fermentation will be established in 



