STUDIES ON FERMENTATION. 369 



ration, it is readily obtained by introducing a volume of from 

 100 c.c. to 150 c.c, of wort into a 2-litre or 3-litre flask, and 

 shaking it briskly so as to saturate it with air ; it is then poured 

 into a settling-glass, to separate it from the great quantity of 

 froth formed in the shaking, and then, by means of a graduated 

 pipette, 50 c.c. is taken for examination. 



We have spoken of the influence that oxygen has on the 

 activity of yeast, on its development and, consequently', on the 

 progress of fermentation. Moreover, we know, from experi- 

 ments already mentioned, which we communicated to the 

 Academy and the Chemical Society in 1861, that the rapid 

 development of yeast in contact with air is in reciprocal relation 

 to the disappearance of the oxygen from the air. Knowing 

 the conditions of the aeration of wort from the moment when it 

 arrives on the coolers until the moment when, in the fermenting 

 tun, it is about to be pitched, it would be interesting to ascer- 

 tain what happens to the oxygen dissolved in the wort at the 

 moment of pitching, how yeast is affected when suddenly 

 brought into contact with that oxygen ; what part, in short, 

 that gas plays in fermentation. 



Let us therefore follow up, hour by hour, the degree of satu- 

 ration after pitching, in Tourtel's brewery. On November 4th, 

 1875, some wort at 14° Balling was pumped on to the coolers at 

 7 p.m., and at 4 a.m. went down to a 32-hectolitre (700 gallons) 

 tun, its temperature then being 6° C. (42'8° F.) The pitching, 

 in which about 100 grammes (3*2 oz. troy) of pressed yeast was 

 used per hectolitre (22 gallons), took place at 5 a.m. The 

 following is the curve of the degrees of saturation of the 

 oxygen, as drawn by Messrs. Calmettes and Grenet. 



The abscissae represent the time expressed in hours, and the 

 ordinates give the degrees of saturation of the wort with 

 oxygen. It will be seen that about twelve hours after the 

 pitching, and at a temperature of 6° C, all the oxygen had 

 disappeared, absorbed by the yeast. We shall find that wort 

 by itself, unassociated with yeast, would also have combined 

 with oxygen ; but in the course of twelve hours, at 6° C, this 



B B 



