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CHAPTER VI. 



THE PURE CULTURE OF YEAST ON A 

 LARGE SCALE. 



Industrial Application. 



the industrial application of pure cultures of systematically 

 selected yeasts inaugurated by Hansen and the author, it 

 became possible to carry out fermentations with certainty 

 in a way that was impossible so long as an unknown yeast- 

 mass was used containing not only a mixture of culture yeasts, 

 but also wild yeasts, bacteria, and even moulds in certain 

 oases. Such selected races can be preserved by appropriate 

 means for a long time as small cultures which can be developed 

 afresh into mass cultures.* 



One very important result of the adoption of the process 

 was to prove that the visible fermentation phenomena do not 

 in general give any insight into the purity of the fermentation. 

 On the other hand, these phenomena may sometimes give 

 valuable information regarding the condition of the yeast, 

 which is directly connected with the nature of the nutritive 

 liquid. 



A real knowledge of the purity of fermentation can only 

 be gained by a biological analysis combined with a micro- 

 scopical examination. 



Pasteur demonstrated the harm that bacteria can do when 

 they develop in alcoholic fermentation, and at the same time 

 he emphasised the importance of the oxidation of the nutritive 



* The important point in preparing a pure culture is the selection of the right 

 .species ; not the purely mechanical isolation of an individual cell. It demands 

 insight into the particular branch of the industry concerned. The point to bear 

 in mind in preparing such cultures is that a yeast actually in use in the industry 

 must form the starting point. 



