DIFFERENT KINDS OF YEAST 79 



DIFFERENT KINDS OF COMMERCIAL YEAST 

 PREPARATIONS 



In the early periods of bread making there were no 

 means of obtaining pure yeast. Gradually, however, we 

 have learned to cultivate the yeasts by themselves, until 

 at the present time there are quite a number of methods 

 for producing tolerably pure masses of yeast. The chief 

 preparations of this sort are given in the following pages 

 and all one species, known as Saccharomyces cerevisice ; but 

 although belonging to one species there are a number of 

 varieties differing in several characters. 



Compressed Yeast. At the present time the yeast most 

 commonly used by the housekeeper is the compressed 

 yeast cake. This well-known commercial article consists 

 of a soft, somewhat soggy material, composed of large 

 quantities of yeast plants mixed together with a certain 

 amount of starch and a varying quantity of other material. 

 This yeast is originally a distillery yeast, which the manu- 

 facturers of certain alcohol products sow in large vats 

 containing materials upon which the plant feeds readily. 

 The yeast grows vigorously and after a time collects as a 

 scum on the surface of the vat. This is removed, washed, 

 and the water partly removed ; then the mass is pressed 

 into cakes and sold to the public. 



This compressed yeast is the most convenient and reli- 

 able type of yeast culture that has been produced. In 

 the fresh cake nearly all of the yeast plants are alive and 

 vigorous, and the results obtained from their use are almost 

 uniformly satisfactory. Compressed yeast has one disad- 

 vantage : it will not keep long, and hence must be used 



