320 MICRO-ORGANISMS AND FERMENTATION. 



formerly groped blindfold, and everything was a matter 

 rational of guess work, a path has now been opened to a 

 technique." 



Hansen is here referring to the two races of yeast that 

 were first isolated and described. 



To what extent individual types display a pronounced 

 character in their practical application depends largely on 

 the nature of the treatment. Thus the degree of fermentation 

 is determined both by the composition of the liquid and by 

 the other conditions of fermentation. A race which gives 

 a vigorous fermentation, can obviously only display this 

 property under certain conditions. On the other hand, 

 typical characters exist which may become noticeable under 

 very different external conditions. Thus it was shown by 

 the author, in the earliest stages of the development of 

 this important reform, that top-fermentation species from 

 the brewery, which have a definite influence on the odour 

 and flavour of the fermented liquor, can be recognised by 

 this fact when they are used in breweries in distant countries, 

 where both the raw materials and the methods of working 

 may be entirely different. The same applies when such 

 species are introduced in absolutely pure cultures, which, 

 beginning on the small scale with one or two litres of thin 

 yeast liquor, are propagated by degrees in brewery wort, and 

 thus adapted to it. 



The two first races obtained as pure cultures, referred to- 

 by Hansen in the above quotation, were Carlsberg No. 1, a 

 yeast applied for many years in the Carlsberg brewery in 

 Copenhagen, and Carlsberg No. 2, which was introduced from 

 a German into a Copenhagen brewery, the fermentation being 

 under the control of the author. After he had drawn attention, 

 to the remarkable fermentation phenomena observed with 

 this yeast, which differ widely from that of Carlsberg No. l y 

 it was introduced into the Carlsberg brewery and isolated as a 

 pure culture by Hansen and the author. 



In 1885 the author had the opportunity of answering the 

 question w r hether different races or species of 8. cerevisice exist, 

 the answer being based upon his own investigations of these 

 two species. 





