118 MICRO-ORGANISMS AND FERMENTATION. 



in cheese factories to regulate the ripening of cheese. They 

 are always added to raw milk, as it is of importance that other 

 species of bacteria from the milk which play a part in the 

 process should not be suppressed. Attempts have also been 

 made to apply cultures of other bacteria and of moulds in the 

 preparation of cheeses of pronounced character e.g., Roque- 

 fort, Camembert, etc. 



As the mash in distilleries is not allowed to exceed a 

 temperature of 70 C., in order that the diastase may be 

 preserved, many of the germs adhering to the raw materials 

 are not killed, but are capable of developing during fermenta- 

 tion, and thus they may not only utilise the nutritive sub- 

 stances, but also disturb the desired alcoholic fermentation ; 

 in the latter respect, butyric acid bacteria are specially dreaded. 

 With the view of preventing too strong a development of 

 germs injurious to the yeast, various acids have been added 

 direct to the mash, or else a lactic 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- 5 5 C., till 

 it shows about 2| of acidity,* corresponding to about 1 per 

 cent, of lactic acid. At this temperature the desired 

 species of lactic acid bacteria develop, whereas it is too 

 high for the majority of bacteria. An excellent means for 

 maintaining the mash at this temperature is the acid chamber 

 introduced by Kruis into distilleries, a small and well-isolated 

 space in which the air maintains a constant temperature, 

 and in which the mash to be soured is introduced and allowed 

 to stand quietly as soon as it has cooled down to the same 

 temperature. The mash is then heated up to 70-75 C., 

 whereby part of these bacteria are killed. After subsequently 

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

 is not affected by this quantity of lactic acid. After it has 

 developed sufficiently, the mixture is employed for pitching 

 the principal mash. To devise a rational process for pitching 

 the lactic acid mash with bacteria, a part of the mash must be 

 placed on one side before yeast is added, and used to start the 



* i.e., 2i c.c. of normal caustic soda solution are required to neutralise 20 c.c. 

 of mash. 



