56 PURE CULTURES OF 



regulated by the cock above the filter, so that a little air 

 passes out through the bent tube and through the water in 

 d every few minutes. The slow intermittent bubbling of 

 the air through the wort can also be heard when the ear is 

 placed against the cylinder. When the latter is jacketed, 

 the current of air can only be observed by means of the 

 water indicator d ; it is evident that the air may also be 

 passed over the fermenting wort through the tube e. With 

 regard to the influence of aeration, no rules of general applica- 

 tion in practice can as yet be given. 



By means of the windows a previously mentioned, it is 

 possible to observe the surface of the liquid. No sufficient 

 information can, however, be gained in this manner, and as 

 the windows are liable to crack during steaming and may 

 become a source of infection through not being perfectly 

 air-tight, they are preferably omitted altogether. The 

 arrangement of the apparatus readily permits also of the 

 withdrawal of samples for controlling the fermentation, large 

 samples being drawn off at /, and small ones at/. Experience, 

 however, soon teaches how the fermentation is proceeding, 

 and the right time for withdrawing the yeast can then be 

 determined with sufficient precision without the previous 

 examination of samples. We must recollect that our object 

 is merely the cultivation of pitching yeast, and not the pro- 

 duction of beer of a definite character. The resulting beer 

 is, of course, not lost, but is mixed with beer in the brewery. 



When the propagating apparatus was introduced into the 

 Old Carlsberg brewery by Capt. Kiihle and myself, the 

 question at once arose in our minds whether, after long 

 usage of the fermenting cylinder, the beer and the yeast 

 might not gradually assimilate bitter principles as, if such 

 were the case, a frequent cleansing of the apparatus would 

 be necessary. It was found, however, that this did not 

 occur, and an experience extending over several years has 

 since fully confirmed this result. In Old Carlsberg, the 



