CHAPTER V 

 MICROBIOLOGY OF FERMENTED FOODS 



COMPRESSED YEAST* 



It is stated that bread over four thousand years old from the tombs 

 of ancient Egypt has been found to contain dead yeast cells, indicating 

 the antiquity of the use of yeast in bread making. The leavened 

 bread of the ancients doubtless contained yeast in combination with 

 other microorganisms. " Potato yeast starters" for bread making 

 were a later development but antedate the manufacture of compressed 

 yeast as we now know this industry. With the development of brew- 

 ing it was found that the yeast left in the fermentation vats was suitable 

 for bread making. In England a great deal of brewers' yeast is still 

 used for this purpose; housewives, rather than commercial bakers, are 

 the principal users of this yeast. Experience has shown that brewers' 

 yeast is weaker than distillers' yeast and, therefore, less suitable for 

 breadmaking; brewers' yeast also is often very bitter from the presence 

 of hop resins. Because of these facts commercial bakers came to 

 prefer distillers' yeast, which at first was a by-product of the alcohol 

 or potato spirits factory. This by-product yeast varied greatly in 

 strength and general quality and a demand arose for a yeast of more 

 uniform character. As a result of this demand suitable pure strains of 

 yeast were selected and propagated for breadmaking the alcohol in 

 this case itself becoming a by-product and yeast the primary product. 

 The compressed yeast and yeast cake industry has now reached great 

 proportions and represents a very striking example of the successful 

 application of science to industry. 



Although the manufacturing processes are carefully controlled 

 analytically and bacteriologically and although a great deal of valuable 

 research work has been done in recent years, little of the information 

 thus obtained has been made available to microbiologists. However, 

 the Wahl-Henius Baking Institute and others are doing much to dis- 

 seminate and to increase the existing knowledge on the subject. 



* Prepared by W. V. Cruess. 



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