On Lactic acid fermentation in milk. 



Proceedings of the Section of Sciences, Kon. Akademie van Wetenschappen, Amster- 

 dam, Vol. X, 1907, p. 17 34. Verscheen onder den titel Over melkzuurgisting in 

 melk in Kon. Akademie van Wetenschappen, Wis-en Natuurk. Afd., Amsterdam, Deel XV, 

 1907, biz. 883 901; en onder den titel Fermentation lactique dans le lait in Archives 

 Neerlandaises des Sciences Exactes et Naturelles, Haarlem, Serie II, Tome XIII, 1908, 



P. 356378. 



In milk left to itself, which in consequence of spontaneous infection, contains the 

 more generally distributed germs with certain regularity some special floras are 

 observed, whose composition is chiefly controlled by two factors: temperature and 

 oxygen pressure. If the latter is very slight, that is, if the microbes of the milk are 

 reduced to more or less anaerobic conditions, the floras become simple of composition 

 and produce certain fermentations. The three principal of these are the Aerobacter-, 

 the Butyric acid- and the Lactic acid fermentations, of which the two first are al- 

 ways characterised by the evolution of hydrogen and carbonic acid, whilst in the 

 lactic acid fermentations, which may occur under different forms, beside the lactic 

 acid, no gas at all, or carbonic acid only is formed. Sometimes this fermentation is ac- 

 companied by a vigorous slime formation, which slime consists of the swollen cell 

 walls of the inferred lactic acid ferments. 



For domestic purposes the lactic acid fermentation should be considered as use- 

 ful; both the others as noxious. 



The fermentation experiment the dairy industry applies to judge of the purity 

 of milk has for its object to determine the commonness or the rarity of the germs of 

 Ae'robacter and of the butyric acid ferment. To this end a high standing glass is 

 filled with milk, placed in a water bath of 40 C. and it is observed whether any fer- 

 mentation gas is evolved, and if so, after how much time. In good milk this produc- 

 tion of gas does not occur because then the lactic acid ferments develop so quickly 

 that the other microbes are expelled. Artificially the Aerobacter fermentation is 

 easily obtained by infecting non-acidified milk with faeces, soil or canal water and 

 cultivating at about 37 to 40 C. After 6 to 12 hours production of gas is observed 

 originating from Aerobacter coli or more rarely from A. aerogenes. The nature of 

 the thereby obtained varieties changes with the temperature. 



At temperatures beneath 40 the Aerobacter fermentation, after lasting some 

 hours, is replaced by a butyric acid fermentation which again, after some time is 

 succeeded by a lactic acid fermentation. Externally the Aerobacter and the butyric 

 acid fermentations cannot be distinguished, but this can be done easily with the mi- 

 croscope. 



