APPLICATION OF THE MICROSCOPE TO THE SELECTION 

 AND CONTROL OF YEAST EMPLOYED FOR BREWING 

 PURPOSES. 



By A. Chaston Chapman. 



The application of the microscope to the selection and control of 

 yeast in the brewery may be said to date from the publication in 

 1876 of Pasteur's " Etudes sur la Biere." In this he made his 

 famous pronouncements *' That every unhealthy change in the quality 

 of beers coincides with the development of micro-organisms foreign to 

 brewer's yeast properly so-called," and that " the absence of change 

 in wort and beer coincides with the absence of foreign micro-organ- 

 isms." 



By " foreign micro-organisms " in the above statements Pasteur 

 referred solely to bacteria, and it w^as some years later (1879) that 

 Hansen outlined his method of making pure cultures of yeast starting 

 from a single cell. As a» result of the application of this method, he 

 showed that some of the yeast species which were frequently present, 

 both in the pitching yeast of the brewery and in the air, were capable 

 of producing " diseases " in beer quite as serious as those produced 

 by bacteria. By a study of ascospore formation and other biological 

 characters of the various species, it was found possible to make a 

 distinction between the culture yeasts and the so-called " wild " 

 yeasts sufficiently definite to enable one cell of the latter to be detected 

 in the presence of at least 100 cells of culture yeast. By means of 

 the microscope, therefore, it is possible to detect the contamination 

 of the pitching yeast, not only with bacteria, but also with other 

 undesirable yeast species, and to take the necessary steps to purify it. 



Lantern slides representing culture yeasts and a number of the 

 " wild " yeasts in illustration of the above statements were shown. 



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