20 NATURE-STUDY REVIEW [12:1— Jan., 1916 



bread. The mineral matters help to accelerate the processes 

 which go on. The ferments and bacteria cause various fermenta- 

 tions, some favorable, like the changing of starch into sugar, 

 mentioned above, and some injurious. Practically all of these 

 flour ingredients affect the taste of the bread and all except the 

 injurious bacteria are or make food. 



Besides flour we may use milk, valuable for its water, sugar, fat 

 and protein; eggs, containing water, fat and protein; and butter or 

 lard, largely fat. All of these are foods and also add flavor. 

 The principal value of salt is its taste. Its great fault is that it 

 retards fermentation by yeast, and so must be put in last. It 

 partly makes up for this bad trait, however, by checking the 

 action of unfavorable ferments. Several of the foods just men- 

 tioned are acted upon by other yeast ferments than zymase. 



In making bread it is necessary to distribute the yeast evenly 

 or the bread will rise unequally. Therefore, we dissolve it in warm 

 water and knead it into the dough. We leave it in a warm place 

 because a temperature of from 77-95 degrees is the best for the 

 action of the yeast. If we leave it too short a time the dough does 

 not rise enough; if too long, the carbonic acid gas passes off and 

 the dough falls. In the morning the bread is full of big bubbles 

 of gas and we knead it again so that they may be broken into 

 smaller ones and scattered through the dough. Thus we try for 

 a bread with many little holes rather than for one with many 

 large ones. 



In baking, the yeast is soon killed by the high temperature; but 

 the gas, expanded by the heat, continues to raise the dough in its 

 effort to escape. Thus we need an oven hot enough to make a 

 crust quickly and so retain the gas until the gluten has hardened 

 sufficiently to hold the spaces. If the oven is too hot the inside 

 of the bread, which heats slowly and to a temperature not much 

 above the boiling point on account of the presence of so much water 

 will be uncooked when the crust is on the point of burning. 



In the meantime the alcohol, which boils at a lower temperature 

 than water, has been helping puff up the dough, has softened the 

 gluten so that it will be better able to hold the gas and has checked 

 the action of the bacteria. This and a few by-products such as 

 glycerine and oxalic acid either are evaporated or else remain 

 in such small amounts as not to be detected. 



Eventually the raw food materials are brought to that stage 



