WHAT IS BREAD RAISING 



87 



The yeast begins to feed upon the materials in the 

 dough and ferments the sugar, producing carbon dioxide 

 and alcohol. Both of these materials remain for a while 

 in the dough, the alcohor dissolving in the water, and the 

 carbon dioxide accumulating as a gas in small bubbles. 

 The dough is so sticky and heavy that it is not possible 

 for these bubbles to rise up 

 through the dough as it does 

 in ordinary fermented liquids 

 (Fig. 31). The gas, there- 

 fore, simply collects as small 

 bubbles in the midst of the 

 dough, causing the dough 

 to swell. This is the so- 

 called raising of the bread, 

 and the bread maker must 

 learn from experience when 

 it has progressed suffi- 

 ciently. After the dough 

 has been properly "raised" 

 by the yeast, it may be 

 seen to be filled with holes 

 occupied by the gas bub- 

 bles (Fig. 42). Now, after the proper kneading, it is put 

 in the oven for baking. The heat of baking drives off 

 the small amount of alcohol which is contained in the 

 bread. The heat also expands the bubbles of gas so as 

 to enlarge the little holes in the dough, thus causing 

 it to swell still more ; but while this is being done 

 the heat hardens the dough into the firm texture of the 

 baked bread, and the holes previously occupied by the 



Fio. 42. The same dough after 

 yeast has grown and caused the 

 dough to swell up by the accumu- 

 lation of carbon dioxide. 



