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PURE YEAST CULTURE. 265 



some experiments made with cider must. He made use of 

 seven species of yeast, experimenting partly with each sepa- 

 rately and partly with mixtures, and his experiments were 

 arranged so as to approximate as nearly as possible the 

 conditions obtaining in practice. The yeasts were obtained 

 from different French ciders. It was found that some of 

 them gave a good product whilst others did not, and that 

 good cider could be obtained by the use of a pitching yeast 

 consisting only of a single species. 



Dr. Nathan of Rottweil was, however, the first to under- 

 take experiments in practice in this field. He published his 

 report on these in the journal * Der Obstbau ' (Stuttgart) in 

 1891 and 1892. Nathan is not merely a theorist, but is also 

 a practical man of great experience in this field. His experi- 

 ments are all the more important since they were carried out 

 on a very large scale. They show that the quality and the 

 whole character of the different fruit wines and the cider 

 depends more upon the species of yeast which plays the 

 main part during fermentation than upon the must. In his 

 report of 1892 he writes : "When I examined the 40 vessels 

 which I had filled with the same must, either from berries, 

 apples or pears, and afterwards inoculated, each with one 

 species or race of yeast, the fermentation products differed 

 in some cases to such a remarkable degree that no one would 

 have thought that one and the same material had been 

 dealt with. Whilst certain races of wine yeast, for instance, 

 imparted a vinous taste and odour, it was found that others, 

 again, had very little influence on the taste of the cider. 

 Several imparted to the must a very disagreeable after-taste." 

 Nathan found, further, that his yeasts not only differed from 

 each other in that they imparted a different character to the 

 product, but that when examined by my method of analysis 

 they also showed good biological characters. The must em- 

 ployed in his experiments was to a great extent freed from 

 germs by means of Bergh's centrifugal apparatus. 



