348 STUDIES ON FERMENTATION. 



it has not been subjected to the action of oxygen during its 

 formation. 



If a great depth of wort, the surface of which alone is in 

 contact with atmospheric air, is left to cool down, it will act in 

 almost exactly the same manner as that which is cooled under 

 an atmosphere of carbonic acid gas, because the oxygen of the 

 air is very slow in pervading wort that is undisturbed. The 

 gas will be taken into solution by the upper layer only, whilst 

 the bulk of the liquid will remain unaffected by it. In some 

 experiments which we conducted in a vessel which contained 

 wort to a depth of 70 centimetres (27'5 inches), and which was 

 provided with a tap that enabled us to draw off some of the 

 liquid every day, until we had reduced the depth to 35 centi- 

 metres, we found, at the end of eight days, that there was not 

 a trace of ox5'gen in solution at the latter depth. It is even 

 probable that, considering the slow diffusion of the oxygen, on 

 the one hand, and the combination that may take place between 

 it and certain components of the malt, on the other hand, it 

 would take a long time for all the wort, if undisturbed and 

 of a certain depth, to become saturated with oxygen. In the 

 vessel represented in Figs. 76 and 77 there is a considerable 

 depth of wort to cool down. Nevertheless, the mere fact of the 

 possibility of an aeration from the surface, whilst the wort is 

 cooling down in contact with pure air, is enough to account for 

 a certain effect that is produced on the yeast, later on, for the 

 more youthful appearance of the yeast of the deposit, compared 

 with that which we find in the case of wort cooled in the 

 presence of carbonic acid gas. The difference between the 

 results is particularly striking if, in both cases, we follow up 

 microscopicallj'- the development of the yeast during the first 

 few davs succeeding the pitching. 



The influence of the air on fermentation is considerable. In 

 the ordinary process of brewing, fermentations would be almost 

 impossible, and in every case most defective, if the wort, before 

 being run into the fermenting vessels, were not aerated by its 

 passage over the "coolers," where the aeration is more or 



