560 Introduction to the Study of Science 



kneaded with firm pressure for about fifteen minutes, in order 

 to mix thoroughly the ingredients, until it becomes elastic and 

 blisters of gas form near the surface. The dough is put into a 

 covered bowl and kept at a constant temperature not lower than 

 75 F., until it rises to two and one half times its original volume. 

 It is again kneaded lightly, with just enough flour for handling, 

 in order to break up the large bubbles of gas and make the dough 

 of fine texture. It is shaped into loaves, which are allowed to 

 rise to twice their volume before being placed in the oven. 

 The baking, which requires about one hour at a moderate tem- 

 perature, stops further change in the dough. The heat changes 

 the starch on the surface of the loaf to a brown sweetish sub- 

 stance, called dextrine, which forms the crust. 



The rate at which sponge and dough rise depends upon the 

 amount and kind of yeast, the temperature, and the moisture. 

 These conditions are carefully controlled in the modern bakery. 

 The bakery methods generally are such as to bring about a 

 rapid rate of rising, whiteness and fineness of texture of bread 

 with less frequent kneading. All these results are obtained by 

 using a large amount of relatively pure yeast, with sugar and 

 the right degree of temperature and moisture. 



Bakery bread is usually whiter and finer in texture than the 

 homemade product, but it dries out quickly and has at no time 

 the flavor and keeping qualities of bread made in the slower 

 way. Sometimes certain materials are used to whiten and 

 refine the bakery bread ; these do not as a rule add to the food 

 value and may decrease it, and are therefore undesirable. 



In many parts of this country and in Europe it has long been 

 a practice to keep a small lump of dough from one baking for 

 leavening the next sponge. The bread produced is slightly 

 different from that made with the usual yeast cake. It has a 

 richer flavor and other desirable qualities. But the dough 

 develops an excessive amount of acid because of a certain kind 

 of fermentation which occurs. 



Why dough rises. We have now to inquire into the causes 



