94 RESEARCHES ON YEASTS. 



yeast which had been grown in wort aerated in the ordinary 

 manner behaved normally as regards clarification and attenu- 

 ation during the first or the second fermentation in the 

 brewery; on the other hand, the yeast which had been 

 grown in the non-aerated wort hehaved in another manner 

 altogether, and this was especially the case with Carlsberg 

 yeast No. I. Through a number of successive fermentations 

 in the brewery this yeast behaved very unsatisfactorily as 

 regards clarification, and the attenuation was abnormally 

 strong. After a time the yeast certainly improved, but it 

 did not return to its ordinary condition in which it existed 

 at the commencement of the experiment. Carlsberg yeast 

 No. 2, under similar conditions, likewise proved less satis- 

 factory than usual (as regards clarification) at first, but in a 

 short time (after two primary fermentations in the brewery) it 

 returned to its normal condition, and behaved in the manner 

 desired. The influence to which the cells were exposed in 

 the two series of experiments, with aerated and non-aerated 

 wort, thus acted in the same direction in the case of both 

 species of yeast. The cells which were grown in the non- 

 aerated wort lost, at least for a time, the property of acting 

 normally under the conditions obtaining in the brewery. A 

 specific difference was, however, distinctly noticeable, in that 

 the Carlsberg yeast No. 2 very quickly returned to its normal 

 state, whilst the Carlsberg yeast No. I did not. The latter 

 species, in fact, not infrequently causes trouble with respect 

 to the brightening of the beer. 



In order to ensure a good result in the direction men- 

 tioned, it seems to be of considerable importance that the 

 wort should be aerated, and especially at a high temperature. 

 As I have mentioned elsewhere, no rules of general applica- 

 bility can, however, as yet be laid down. My object was 

 merely to show how changes of an undesirable character 

 can occur in brewery yeasts when the wort in which the 

 yeast is grown has not been properly aerated. 



