266 ECONOMY OF THE HOUSEHOLD. 



a smooth and clastic dough. This dough consists of 

 gluten, so called from its sticky or glutinous character, 

 and starch. These two substances, as we have seen, may 

 be readily separated. 



965. If we add a little yeast to the flour while mixing 

 with water to form dough, and let it stand some hours in 

 a moderately warm place, the dough begins to ferment 

 and rise, increasing considerably in bulk. 



966. In rising, little bubbles of carbonic acid gas are 

 set free throughout the mass of dough, and this it is 

 which makes the bread porous and light, by the stretching 

 or expansion of the tenacious gluten. Set the dough in 

 a hot oven, and the fermentation and rising are first 

 hastened by the elevated temperature. But when the 

 whole is heated up to the point of boiling water, the 

 process is suddenly stopped, and the mass is fixed by the 

 baking in the form it had taken when the rising was 

 suddenly arrested by the heat. 



967. But why is the rising so suddenly checked in the 

 oven ? The yeast we have added to the dough is in 

 reality a living plant, which grows or increases with great 

 activity when it comes in contact with the moisture of the 

 dough, producing what we call fermentation or rising. 



968. During this process, a part or the starch in the 

 flour is changed into sugar, and this sugar into alcohol 

 and carbonic acid gas. This gas cannot escape from the 

 dough as the elastic gluten expands, but it remains in the 

 shape of bubbles. At last the heat becomes great enough 

 to destroy the yeast plant, and the process of rising ceases. 

 The alcohol mostly escapes in the baking. 



969. After the loaf is sufficiently baked, if we cut it 

 through we find it is spongy and full of little cavities, 

 made by the gas bubbles during the rising. It is then 



