72 MICRO-ORGANISMS AND FERMENTATION. 



capable of developing during fermentation, and thus not only 

 may they utilise the nutritive substances, but also disturb the 

 desired alcoholic fermentation; in the latter respect, the butyric 

 acid bacteria are specially dreaded. With the view of prevent- 

 ing a strong development of germs injurious to the yeast, 

 various acids have been added direct to the mash, or else a lac- 

 tic acid fermentation has been previously carried out in a 

 fraction of the mash. Thus a tenth part may be kept at a 

 temperature of 50 C. till it shows about 2 \ degrees of acidity, 1 

 corresponding to about 1 per cent, of lactic acid. This 

 temperature is the most favourable for the desired species of 

 lactic acid bacteria. The mash is then heated up to 70C. 

 whereby part of these bacteria are killed. After subsequently 

 cooling down to about 20C. the yeast is added. The latter 

 is not affected by this quantity of lactic acid. After the yeast 

 has developed sufficiently, the mixture is employed for pitching 

 the principal mash, putting aside one-tenth of the latter for 

 the next operation. 



The acid thus introduced into the principal mash together 

 with the surviving lactic acid bacteria act as disinfectants, 

 besides exerting an influence on the yeast-cells, both direct and 

 by reacting on the nutritive substances. 



If the whole process is not carried out with due care and 

 regularity, the yield of alcohol will suffer, and infection with 

 foreign ferments may take place. This happens frequently at 

 the beginning of a distilling season, after most of the lactic acid 

 bacteria existing in the fermentation room have died. The 

 attempt has been made to remedy this evil by isolating the 

 bacterium present in an acid mash which had undergone a 

 good normal acidification ; this bacterium was developed into a 

 mass-culture and introduced into the new mash, which was 

 then left for acidification. In this manner LAFAR isolated from 

 the acid mash of a distillery a bacterium which differs from the 

 milk-souring species, and named it Bacillus acidificans longis- 

 simus, on account of its frequent occurrence as long filaments. 

 The experiments hitherto made with this species on the large 

 scale by BEHRENS and LAFAR have yielded good results. LEIGH- 

 MANN and the author have also prepared pure cultures of the 



l i.e., to neutralise 20 c.c. mash 2 c.c. normal caustic soda solution are required. 



