CONSUMPTION OF OXYGEN. 235 



one experiment, to amount to 41.7 and 7 c.c. respectively per 

 litre of wort; but a considerably lower figure (5.7 c.c.) was 

 obtained in the latter case by P. PETIT (III.). A. PETERSEN (II.) 

 detected 2-4 c.c. of oxygen per litre in the worts of the Alt- 

 Carlsburg brewery ; and, finally, CL BLEISCH and R. SCHWEITZER 

 (I.), in investigating the connection between oxygen absorption 

 and the temperature, chemical composition, gravity motion of the 

 wort, determined the amount of the physically dissolved oxygen 

 in wort of 14.4 and 14 Balling, as 2.4 c.c. per litre at 62.5 C. 

 and 4.4 c.c. at 5 C., the chemically combined portion, on the 

 other hand, being 53 c.c. at 85 C. and 4 c.c. at 45 C. The 

 decomposing action of oxygen, whilst very mild at medium tem- 

 perature (15 C.), is nevertheless appreciable when continued for 

 a long time. In this connection reference may be made to the 

 occurrence of formic acid (associated with carbon dioxide) ob- 

 served by EAYMAN and KRUIS (I.) in old, sterile wort exposed to 

 the air. 



The aeration method of yeast manufacture (see vol. ii. p. 184) is 

 based on the observation that cell reproduction is stimulated by 

 powerful aeration, and originated in Sweden, though the first 

 incentive was given by H. HAYDUCK'S experiments (V.), subse- 

 quently followed up by M. DELBRUCK (VI.). Under the stimu- 

 lating influence of oxygen the yield of pressed yeast furnished by 

 this method amounts to 25-30 per cent, of the weight of cereal 

 substances in the mash, as compared with about 12 per cent, in 

 the old method which is now being gradually superseded. 



In the laboratory cultivation of yeast for technical purposes, 

 the aeration of the nutrient medium must not be omitted ; for it 

 has been shown by Hansen, and confirmed by A. JORGENSEN (X.) 

 that beer yeast grown in imperfectly aerated wort gives unsatis- 

 factory results when used in practice, the "break" of the wort 

 especially being defective. 



The influence exerted by oxygen on the progress of alcoholic 

 fermentation will be dealt with in chapter Ixiv. 



