394 STUDIES ON FERMENTATION. 



capacity for oxygen, and pitched with a good " low " yeast, taken 

 from the fermentation of a wort aerated in the same way, and 

 that the beers thus obtained not only possess vastly superior 

 keeping properties, but are equal in quality and superior in 

 palate- fulness to beers brewed with the same wort on the existing 

 system. We should be perfectly justified in forming this con- 

 clusion as to the strength * of the beer furnished by the new 

 process, even if on tasting it we found that the new beer M was 

 merely equal in strength to Tourtel's beer brewed in the or- 

 dinary manner, since the wort in the new process, other con- 

 ditions being the same, is weaker than the same wort treated 

 in the usual way, from not having undergone that evaporation 

 on the coolers which concentrates it. If we were to restore to 

 the concentrated wort of ordinary brewing all the water lost by 

 it through evaporation, the beer that we should obtain would 

 be sensibly weakened. f 



One thing, however, is that we must employ good varieties of 

 " low " yeast. We have seen how the employment of certain 

 forms of yeast renders the clarification of beers difficult, as well 

 as extremely slow, and almost prevents their falling bright at 

 the end of fermentation. These yeasts, moreover, frequently 

 impart to beer a peculiar yeast-bitten flavour, which does not 

 disappear even after a prolonged stay in cask. Even repeated 

 growth of these yeasts, whether in closed or in open vessels, 

 and no matter what quantity of air we may supply them with 



* Eefer foot-note, page 354. 



t The evaporation on the coolers varies according to the arrangements 

 in different breweries ; but in no case is it less than several hundredths 

 of the total volume. One special advantage of the new process is that it 

 gives us, ceteris paribus, a volume of beer that is 5, 6, or 7 per cent, 

 greater than that which we should obtain by the old process, without in 

 any way affecting the strength of the beer. It is easy to ascertain the 

 quantity that evaporates on the coolers, by determining the quantity of 

 water that must be added to a known volume of wort coming from the 

 coolers to bring its density back exactly to that of the original wort, both 

 being calculated to the same temperature. Bate's English saccharometer, 

 which shows differences of nearly yo\3oth in density, may be employed 

 with advantage in this determination. 



