APPLICATIONS OF LACTIC ACID FERMENTATION 109 



tribute towards the aroma in the souring of cream. The author x 

 has isolated this bacterium from commercial starters, and finds 

 it to be a typical milk organism, possibly a variety of 8. cremoris 

 which has lost the power to form acid, but on the other hand 

 developed an increased power to produce aroma. Also Hammer 

 and Baily 2 have shown that the acid-forming bacteria proper 

 produce more volatile acids (which constitute part of the aromatic 

 substances) in symbiosis with another bacterium. Dry cultures 

 may be obtained as well as liquid cultures. The latter are dried on 

 some neutral material such as lactose or starch, and products are 

 obtained which are more permanent than the liquid preparations 

 and better suited for sending long distances. On the other hand, 

 dry cultures will not keep indefinitely, and it is not advisable to 

 buy them unless they are stamped with the date of preparation or a 

 date after which they must not be used. In any case they must 

 be revived by propagating several times before they can be used, 

 and they are, on account of the method of their preparation, much 

 oftener infected with yeasts and moulds than the liquid cultures. 

 Their use is therefore not to be recommended if liquid cultures 

 can be obtained instead. 



The full benefits of the use of pure cultures are only -attained 

 when all the other microorganisms in the cream have previously 

 been killed by pasteurisation, and it was only after this practice 

 had been introduced that commercial cultures came into extensive 

 use. The pasteurisation of the cream and the subsequent use of 

 good cultures have more than anything else contributed towards 

 making Danish butter a uniform and well-keeping product. 

 Pasteurising above 80 C. brings the additional advantage of 

 killing the tubercle bacteria which pass into the cream in large 

 numbers on separating ; the resulting buttermilk will thus be 

 rendered harmless to pigs and calves, and the butter harmless for 

 human consumption. The legal enforcement of pasteurisation of 

 cream at a temperature of at least 80 C. by the law passed, in 

 Denmark in 1898, with the object of combating the results of 

 bovine tuberculosis, must therefore be signalised as an important 

 step forward in Danish dairy practice. 



Although there can be no doubt that the pasteurisation of cream 

 can only be a benefit, it is still maintained by many that the 

 commercial cultures do not produce so strong an aroma in the 

 butter as is obtained by spontaneous souring. Pasteurisation 

 does away with the first stage of spontaneous souring, while the 

 development of yeasts and yeast-like moulds is avoided during the 



1 " The Lactic Acid Bacteria," monograph published in English by the 

 Danish Academy of Sciences, Copenhagen, 1919. 



2 Iowa Agricultural Experimental Station, 1919, Bulletin No. 55. 



