52 PURE CULTURES OF 



is also continued during the process of cooling. Generally, a 

 pressure of from I to 2 atmospheres in the air-holder suffices, 

 It is merely necessary that the sterile air in the cylinder should 

 always exert a slight pressure in excess of the atmospheric 

 pressure, and thus prevent any impure air being drawn in, and 

 ensure the full amount of oxygen being taken up by the wort. 

 It is evident that the operator must not forget to first open 

 the cock n. If this is not done, there is a risk of injuring the 

 apparatus. 



As soon as the wort is ready for cooling, the perforated 

 ring/ is connected with a water tap and the sprinkler allowed 

 to play against the sides of the cylinder until the tempera- 

 ture of the wort is reduced to about 10 C. In an ordinary 

 fermenting cellar this takes about an hour; the further 

 cooling must be effected by means of iced water. The air is 

 passed through the liquid continuously, and in escaping 

 through the bent tube carries some of the wort with it ; the 

 rousing of the wort produces a good deal of foam, but this 

 never gives rise to contamination. The aeration must not, 

 however, be very vigorous or there may be too great a loss of 

 wort. It is only when the wort has cooled to about 11 C. 

 that the foam comes through the tube ; this is rendered less 

 troublesome by introducing warm water into the vessel o. 

 The wort, now ready for undergoing fermentation, is run 

 through the pipe k into the fermenting cylinder. 



In order to avoid rousing the wort by the aeration whilst 

 it is passing into the fermenting cylinder, the filter may be 

 connected with a forked tube, one limb of which is a con- 

 tinuation of the air-tube mentioned above, whilst the other 

 only just passes through the top of the cylinder without 

 coming into contact with the liquid. These two limbs must 

 be so arranged that either can be opened or closed by a cock. 

 The air admitted whilst the wort is being run off has, of course, 

 to pass through the last-mentioned limb. This arrangement 

 is not, however, essential ; some of the cylinders (Fig. 12) 



