26 PURE CULTURES OF 



it is possibly even the rule. What has been stated above 

 explains why in breweries it is at least in many cases advis- 

 able to use wort in which fermentation has just been started 

 as pitching yeast, instead of waiting until the end of the 

 primary fermentation, as is usually done, and using only the 

 sedimentary yeast. It is evident, however, that a true, pure 

 culture cannot be obtained in this way.* In consequence of 

 these observations, I already stated in the first German 

 edition of this book that the sample to be tested for wild 

 yeast is best taken at the end of the primary fermentation, 

 and the sample for the preparation of the pure culture of the 

 brewery yeast at the commencement of the primary fermen- 

 tation, and in both cases from the upper layer of the wort. 

 This point has become of no small practical importance. 



When the brewery yeast, from which it is desired to 

 prepare a pure culture, is moderately pure, the growth taken 

 at an early stage of the fermentation will thus approximate 

 more or less to a pure culture. For our experiments it is 

 therefore advisable to take a sample from the surface of the 

 wort as soon as this has become covered with a slight foam. 

 From this it is comparatively easy to prepare a pure culture 

 of the brewery yeast which predominates, and, in accordance 

 with the foregoing considerations, this is what we require. 



If the brewery is at a distance from the laboratory, it will, 

 as a rule, be best to start with the ordinary sedimentary yeast, 

 and, if this is not enfeebled, it can be used as it is ; otherwise, 

 it is introduced into a flask of sterilised wort, and, as soon as 

 fermentation commences, a little of the liquid is decanted and 

 made use of for the preparation of the pure culture. The 

 object here is not only to obtain a growth in which the 

 desired species preponderates, but also to obtain young and 

 vigorous cells. The latter is of importance in reference to the 

 treatment to which they are subjected in the course of the 



* See also J. Vuylsteke's "Ein Beitrag zur Entwickelungsgeschichte der 

 Mischsaaten von Saccharomyceten," Zeitschr. f. d. ges. Brauwesen, 1889, No. I. 



