SYSTEMATICALLY SELECTED YEASTS. 55 



breweries the fermentation is allowed to proceed to the end 

 of the primary fermentation, and the sedimentary yeast is 

 then removed and employed as pitching yeast. It is evident, 

 however, that instead of proceeding as above, a portion of 

 the fermenting wort may be withdrawn as soon as the yeast 

 cells have multiplied to a sufficient extent (which, under the 

 conditions given would take about 40 hours). This is a more 

 rapid method of procedure than the former, and is adopted 

 with good results in some breweries. Whether the sedimen- 

 tary yeast or the fermenting wort should be made use of 

 must be decided by local conditions and by the nature of the 

 yeast* 



The mouths of the cocks / and k are carefully cleaned to 

 remove the beer and wort remaining in them, as otherwise a 

 growth of bacteria, yeast and mould may develop. For this 

 purpose a steam-hose is best made use of, its end being fitted 

 with a tubular nozzle so that it can be used like a spray. 

 The warm water which first comes out after turning on the 

 steam washes the cock, and the steam which follows will 

 effect its sterilisation. When this is done, the mouths of 

 the cocks are closed by means of clean metal caps which 

 are screwed over them. 



Whilst fermentation is proceeding, the carbonic acid which 

 is produced prevents any air from being drawn in, and con- 

 sequently it is not necessary to pass a current of air through 

 the vessel ; fermentation and yeast production also take place 

 satisfactorily without aeration. If, however, it is considered 

 desirable to employ aeration in order to be able to influence 

 the progress of the fermentation, only a small quantity of air 

 is as a rule passed through the liquid. Its admission is 



* Mr. Jos. Peska informs me that during his stay at Melbourne, as 

 director of the low-fermentation brewery of the Foster Company, the pure yeast 

 culture for a long time gave rise to various difficulties, until it occurred to him 

 to let the yeast become very old ; he accordingly took it out of the fermenting 

 cylinder only once a month. All the earlier difficulties then disappeared, and he 

 got a very satisfactory fermentation. 



