PLANTS THAT CHANGE FOOD 



437 



In modern bread making, yeast, which contains the 

 minute yeast plants, is mixed thoroughly into the material 

 which is to compose the bread; and the bread is then put 

 into a warm place to rise or, more exactly, to allow the 

 yeast plants to multiply. If the materials and the tem- 

 perature are right, the yeast plants multiply very rapidly, 

 feeding upon the material of the dough, and changing sugar 

 into carbon dioxide and alcohol. Little bubbles of carbon 

 dioxide gas are developed throughout the dough, making 

 it slightly porous. 



The dough is then kneaded to develop the elasticity of 

 the gluten and to mix the greatly increased number of yeast 



BREAD MAKING IN MEXICO 



plants uniformly through the mass. It is then set aside 

 again so that the uniformly scattered yeast plants may con- 

 tinue their activities. Bubbles of carbon dioxide form 

 throughout the whole mass, and a light spongy dough 

 results. When this is heated in the oven, the tiny bubbles 

 of gas expand, making a more porous sponge, the alcohol 

 evaporates, and the dough bakes, thus forming light bread. 



