CRYPTOGAMS 255 



216. YEAST 



Object. To determine conditions favorable to the 

 growth of yeast. 



Method. Prepare three bottles of sugar and water. Add 

 yeast to each and place one in a cold place, another in a 

 warm room, and the third on a radiator or other hot surface. 



After several hours examine the three preparations and 

 note results. What conclusion can be drawn at this point ? 



Now put all three bottles in a warm place and let them 

 stand for another period. Result? What conditions are 

 most favorable to yeast? How are these conditions ob- 

 served in bread making ? In brewing ? 



217. YEAST 



Object. To discover the effect of extreme heat on yeast. 



Method. Prepare three bottles of sugar and water and 

 treat them as follows: After adding the yeast, heat one 

 bottle scalding hot and then set it away for observation. 

 Place the other two in a warm place until fermentation has 

 begun, then heat the second bottle scalding hot. Allow all 

 three bottles to stand for several hours longer. Then com- 

 pare the results. 



Conclusion. Why does fermentation not continue after 

 bread is baked ? Give reason for your answer. 



218. YEAST 



Object. To find out what substance is necessary to 

 yeast. 



Method. Prepare bottles containing various substances 

 other than sugar and add yeast as before. Do all substances 

 ferment? Try starch paste, salt solution, fruit juice, flour, 



