130 



CHAPTER V. 



WHAT IS THE PURE YEAST OF PASTEUR?* 



1892. 



i. IN the physiological experiments which I carried out with 

 Saccharomyces apiculatus in 1879 and 1880, I prepared the 

 necessary pure cultures in accordance with the principles laid 

 down in Pasteur's ' Etudes sur la biere.' The following is the 

 account which I gave of the method.f " Into a large number 

 of flasks containing sterilised wort as nutritive medium, 

 fruits were introduced which were assumed to have Saccharo- 

 myces apiculatus on their surface ; one piece of fruit only 

 was introduced into each flask, and only such were chosen 

 which were fairly clean and free from mould, and with a little 

 practice this can readily be discovered with the naked eye. 

 After a few days, one or several of the flasks, as a rule, contain 

 an abundant and fairly pure growth of the desired yeast 

 fungus. Whether bacteria are present or not is of little im- 

 portance, for the latter can generally be easily suppressed by 

 cultivation in acid liquids. Greater trouble is encountered 



* Although this memoir is mainly of a theoretical nature, I have yet felt that 

 it ought to be introduced into my collected writings relating to the fermentation 

 industry. I decided upon this for two reasons : in the first place, the main 

 question treated of is one of great practical interest, namely, what is to be under- 

 stood by a pure brewery yeast ? and, in the second place, the results of my in- 

 vestigations on the effect of treating brewery yeast with tartaric acid are of 

 direct practical importance. 



t Emil Chr. Hansen : " Sur le Saccharomyces apiculatus et sa circulation dans 

 la nature" (' Compte-rendu des travaux du laboratoire de Carlsberg,' i vol. 

 3livr. 1881). 



