'Rural School Leaflet. 1059 



sa.tisfy the yeast plant. In feeding on sugar, yeast converts it to 

 alcohol and a gas known as carbon dioxid. This gas causes spoiling 

 fruit to bubble, but is useful in bread-making, for it gets caught in the 

 meshes of the dough and stretches it, causing it to rise. If the crop of 

 yeast plants in bread dough is good and vigorous there is a large yield 

 of carbon dioxid and the bread rises well 

 and is light. 



Yeast cannot stand a great deal of heat, 

 and if it is sowed in a field of very hot 

 liquid it is quickly killed. This is particu- 

 larly true of the cultivated yeasts used in 

 bread-making, for the wild yeasts are likely 

 to be more hardy. If we are canning fruits 



it is very desirable to boil them so as to p^^_ Sg.-Growing yeast cells 

 destroy any wild yeast which may be present, 



for in that case the yeast is a weed because it is growing where it is not 

 wanted. In making bread, howev£r, we must be careful not to have the 

 liquid hot since it is our desire to make the yeast grow. The temperature 

 most favorable to the growth of yeast is 70 to 90. degrees F. It may 

 be lower than this and then the yeast grows slowly, or it may be some- 

 what higher, but this may weaken the yeast and thus make it a prey 

 to its enemies, and if we are using the yeast for any purpose they may 

 spoil our results. 



The enemies of the yeast plant are just as small and invisible as it is, 

 and because we cannot see them we must not take it for granted that 

 they are not there. They may be found on soiled towels and hands or 

 unclean utensils; in milk and water and poor flour; and if they get into 

 our yeast garden, they may choke out the yeast and grow in its place. 

 Then if we are using the yeast to make bread, instead of having sweet, 

 well-risen bread, we shall find a sour poor loaf which is neither good nor 

 wholesome. If the yeast is to grow vigorously and produce new plants, 

 it must have not only food but considerable moisture. It may be kept 

 alive for a long time in a dry state, but will then be quiet and inactive. 

 The dry yeast cake and the compressed yeast cake so familiar to house- 

 keepers are fields of dried-out yeast plants, alive but inactive, and re- 

 quiring only moisture, warmth, and food to start fresh growth. 



In former times bread was made light by setting some dough in a 

 warm place until it began to ferment. That was before anything was 

 known about yeast and no one dreamed then that the fermentation was 

 due to certain little wild plants which had found their way from the 

 air into the dough. In some households is still found a kind of bread 



