SYSTEMATICALLY SELECTED YEASTS. 37 



in non-aerated wort was unsatisfactory in this respect and 

 only became normal after several fermentations. Similar 

 observations have also been made by Aubry and A. Jorgensen.* 

 This phenomenon is deserving of further study. In accord- 

 ance with our present experience it is, therefore, advisable to 

 work with aerated wort ; and this is of great importance also 

 for another reason if it is desired to obtain a compact sedi- 

 ment of yeast in the vessel. This applies especially to species 

 like Carlsberg bottom yeast No. I. That the wort in the flasks 

 and metal vessels does take up oxygen from the air on stand- 

 ing at the ordinary room-temperature was very easy to prove. 

 In fact, after four months, the sterilised wort was found to 

 contain more free oxygen than the normally aerated wort from 

 the open coolers. Some experiments with Carlsberg bottom 

 yeast No. I, which under normal conditions is not a good 

 clarifying yeast, have shown that it is of especial importance 

 to thoroughly aerate the wort whilst still hot. 



In most laboratories the Carlsberg vessels are treated in 

 the manner described above, and thus no special arrange- 

 ments are made for the aeration of the wort. In my 

 laboratory it is customary, however, to pass a considerable 

 volume of sterilised air into the wort whilst it is still boiling. 

 This air passes from a holder in which it is contained under 

 a pressure of 3-4 atmospheres, and is purified from all germs 

 by means of the cotton-wool filter described on p. 66. For 

 greater security against infection, the bent tube through 

 which the steam escapes is heated in a flame. A sterile 

 glass tube is inserted into the rubber tube near the bottom 

 of the vessel and is connected with the cotton-wool filter ; 

 the pinch-cock is then opened and the air-cock turned on 

 at the same time. As soon as aeration has thus commenced 

 the flame under the vessel is turned out, and a few minutes 

 later also the lamp employed for heating the bent tube. 

 Aeration is continued until the temperature of the wort has 



* Zeitschr. f. d. ges. Brauwesen 1890. 



