Ill 



189 



is not rendered more free from germs than by heating to 70°. The bacteria of putrefaction 

 were subdued in the experimental cheeses inoculated with lactic acid bacteria; whereas 

 in the control cheese not inoculated, they developed so abundantly that these latter often 

 contained more S.V than the former. \Ve were therefore obliged to disregard the results 

 of the chemical investigations, and be content with a purely practical estimate, from taste 

 and structure alone. If an experimental dairy should ever be established in Denmark, we 

 hope to be able to resume the experiments with milk containing fewer bacteria. For the 

 rennet, we used Hansen's tablets, these being practically free from germs, which is by 

 no means the case with the usual rennet extracts. 



As our experimental cheeses constantly proved better than our control cheeses, we 

 can only say that all the lactic acid bacteria thus tested produce a favourable effect upon 

 cheese, if only by subduing the putrefaction bacteria and furthering the proteolytic action 

 of the rennet. An exception, however, is found in Sc. liquefaciens, which, as F'relden- 

 REicH has already shown, renders the cheese bitter and makes it run. In cheeses with pure 

 cultures of this streptococcus, we found up to 80 % SN. Tc. liquefaciens also can make the 

 cheeses rather soft, but can also give them, as we have noted before, a flavour resembling 

 that of -Danish Swiss cheese", or Russian Steppe cheese". The best effects are obtained 

 with Sbin. casei, which is a cheese ripening bacterium par excellence, but also the casein- 

 splitting strains of Sc. laclis and Sc. cremoris gave an extremely good cheese, so that we 

 can willingly agree with Barthel^) that a greater importance should be ascribed to such 

 streptococci in the ripening of cheese than has hitherto been conceded. Even Sc. glyceri- 

 naceus, which does not break down casein, had a favourable effect on the ripening of the 

 cheese. Sc. fæciutii, Sc. thermophilus, Sc. inulinaceus, Sbm. planlarum, betacocci and beta- 

 bacteria do not as a rule affect the flavour. Vigorous strains of the two last-mentioned 

 groups can occasion some formation of holes. The great importance attaching to certain 

 thermobacteria, especially Tbni. helveticum. in the ripening of strong heated cheeses, is 

 a point we need not here discuss further. In non-cooked cheeses, where cooling takes place 

 rapidly, they cannot of course produce any affect. 



It will be seen then, that many different species of lactic acid bac- 

 teria contribute to the ripening of cheese, but there is hardly any doubt 

 that a cheese — as has been proved in the case of Emmenthal cheese — 

 only obtains the proper character when certain definite species are pre- 

 dominant. The bacteria to be used for the ripening of cheese must, like those used for 

 souring of cream, be freshened up for a time in milk, and it will be necessary to make sure 

 that the casein-splitting strains have not lost this power. 



') Meddelande Nr. 97 från Centralanstalten for försöksväsendet på Jordbruksområdet. 1914. do 

 No. 171. 1918. As regards the ripening process of cheese otherwise. I can refer to my Dairy Bacterio- 

 logy 1916. 



