PURE YEAST AND BREWING OPERATIONS. 295 



resulting beers were decanted into bottles containing a 

 small quantity of dry hops. Six days after bottling the 

 beer No. 5 was in a violent fermentation ; No. 4 and No. 

 2 showed a very slight secondary fermentation whilst the 

 other beers were flat. After eleven days No. 5 and No. 4 

 were fermenting excessively, No. 2 and No. 3 very slowly 

 and No. 1 was still flat. The fermentation of No. 2 and No. 3 

 became more marked during the following days but did not 

 reach the intensity of No. 5 and No. 4. The beer No. 1 

 only showed a slight fermentation after a month. At this 

 point the rotatory power of the beers was determined and 

 the deposits were microscopically examined with the results 

 shown in the table. 



These and other similar experiments lead Van Laer to 

 the following conclusions : — 



" (a) When dry hops, with a proper diastatic power, are 

 added to a beer at racking, and if the after-fermentation is 

 not opposed by any mechanical cause, it will always show 

 itself after a more or less extended period, irrespective of 

 the number or the nature of the yeasts used at pitching. 



"(d) If the principal yeast is mixed with even very 

 minute quantities of yeast found in the deposits of beers 

 that have undergone an after-fermentation, the latter always 

 shows itself quicker and with a greater intensity than- when 

 the beer has only been fermented with the principal yeast. 



" (c) The intensity of the after-fermentation depends 

 upon the nature of the yeasts mixed with the principal 

 yeast. Some give rise to an excessively violent fermenta- 

 tion, with production of very light cells, which remain a 

 long time in the beer. Others produce a more moderate 

 secondary fermentation ; among the latter Saccharomyces 

 some very heavy caseous yeasts are found, which the carbonic 

 anhydride only raises with difficulty. It is usually these 

 which produce normal secondary fermentations." 



The question of secondary fermentation in beers, to 

 which no dry hops or no diastatic agent has been added, is, 

 however, of greater interest and importance in connection 

 with the employment of pure yeast. It would in fact 

 appear from experiment No. 1, in the above table, that 



