WHERE DOES YEAST COME FROM? 157 



and tedious investigation that he was able to perfect the com- 

 mercial yeast cakes and yeast brews universally used by bakers 

 and brewers. The well-known compressed yeast cake is simply 

 a mass of live and vigorous yeast plants, embedded in a soft, 

 soggy material, and ready to grow and multiply as soon as they 

 are placed under proper conditions of heat, moisture, and food. 

 Seeds which remain on our shelves do not germinate, but 

 those which are planted in the soil do. So it is with the yeast 

 plants. While in the cake, they are as inactive as the seed ; 

 when placed in dough, or fruit juice, or grain water, they grow 

 and multiply and cause fermentation. 



