3o6 



PHARMACEUTICAL BACTERIOLOGY 



resulting in an alcoholic drink which is said to have a very peculiar flavor. 

 Pressed yeast cakes for bread making are prepared as follows: 



The iiltered saccharine yeast mash in vats, is inoculated with pure 

 cultures of Saccharomyces cerevisem. Active fermentation takes place in the 

 presence of pure air which is supplied through pipes leading into the vat. 



Fig. 79- — Showing the characteristic stellate cells of the pith of some reed used as 

 filtering material in clarifying sak6. Bundles of the pith are placed in the bottom of 

 a perforated cask, forming a layer a foot or more in depth; through this the sak^ perco- 

 lates. The impurities are caught in the intercellular spaces of the pith. 



The white scum or foam which forms is poured on fine sieves, washed 

 with sterile water, and then centrifugalized to remove most of the water. 

 This partially dry material is then pressed into cakes, thoroughly dried at 

 a low temperature, and wrapped in lead foil to exclude air. Starch is some- 

 times added as a dryer, but this is no longer necessary because of the 

 improved methods of manufacture. Good yeast should be of a yellowish 

 color, easily powdered and should have a pleasant "yeasty" odor. 



The so-called Chinese yeast, concerned in various fermentation proc- 



