STUDIES ON FERMENTATION. 347 



conditions is extremely slow, and the fermentation takes from 

 fifteen to twenty-five days ; whilst, under the same circum- 

 stances, but with an aerated wort, it would be finished in from 

 eight to twelve days. This is a considerable drawback, but, 

 perhaps, a still more serious inconvenience is that the beer 

 takes much longer to clarify, and does so with greater difficulty 

 than those beers which are made with aerated worts. At the 

 same time, this is largely compensated by the superior quality 

 of the beer, which is stronger and has greater fulness on the 

 palate, whilst the aroma of the hops is preserved to an extent 

 never found in beers brewed by the ordinary process. Besides 

 this, the 3'east deposited at the bottom of the fermenting vessel 

 is much less active, and, being of an older type, is revived with 

 greater difficulty than that which forms in aerated worts. This, 

 which might be considered a disadvantage, if we had to employ 

 the yeast afterwards for pitching, has the great advantage ol' 

 giving a beer which, "when racked, undergoes its secondary 

 fermentation only slowly, and with difficulty.* A beer of this 

 kiud is better adapted than ordinary beer to stand a long 

 journey without developing great pressure inside the casks, 

 and, if bottled, it will contain very little deposit, and will not 

 froth violently when uncorked. The reason is, that a yeast is 

 the more active, the more ready to multiply rapidlj', and to 

 work vigorously the more highly aerated the wort was in which 

 it was grown. On the other hand, a yeast formed apart from 

 air readily gets exhausted, and may even perish in the liquid in 

 which it ferments, when that is kept out of contact with air ; 

 in other words, the vital action of yeast is more restricted when 



* It has been observed by brewers that, sometimes, without any- 

 apparent cause, a yeast suddenly becomes inactive and fermentation 

 ceases. Accidents of this kind may probably be explained in the same- 

 manner as the facts of which we are speaking. If a wort has not been 

 aerated, or if it has been deprived of oxygen by a commencing develop- 

 ment of microscopic organisms, the yeast formed in it will be very 

 inferior, and the fermentation may stop at its commencement or soon 

 afterwards. In such a case, an aeration of the yeast and wort would be 

 the best remedy. 



