igoo-i.] The Ripening of Cheese. 117 



The cheese made from the control milk did not ripen at all. 

 From these experiments, the authors concluded, that : 



1. The heating of milk changes the casein and prevents ripening. 



2. If we look for the ripening organisms among the lactic acid 

 bacteria, we must remember that not all the lactic acid bacteria are able 

 to cause the ripening. 



3. The theory of Babcock and Russell is incorrect, otherwise the 

 control cheese would have ripened. 



4. If the theory of Weigmann should be confirmed, it must be 

 qualified in so far that the organisms are still alive on the fourteenth 

 day, for the cheese used was inoculated with fourteen day old cheese. 



De Freudenreich and Jensen's experiments on the relation between 

 lactic acid ferments and the ripening of Emmenthaler cheese were very 

 extensive and thorough. They conclude that the Tyrothrix bacilli take 

 no part in the ripening. They did not multiply in normal cheese, and 

 even when added in large numbers they exerted no influence on the 

 decomposition products, in fact their influence was harmful. 



The natural enzymes (galactase) perhaps participate in the ripening, 

 by rendering the casein soluble, and thus facilitate the operations of 

 the lactic acid ferments. Pasteurising deteriorates the quality of 

 Emmenthaler cheese. Another fact brought out was the loss of the 

 soluble constituents of cheese during ripening. 



The results of de Freudenreich's experiments in 1900 confirmed the 

 work of Babcock and Russell upon galactase. Several new facts were 

 also demonstrated. The presence of 0.3 and 0.5 per cent, of lactic acid 

 considerably decreased the action of the diastase. 



Twenty per cent, of ether was added to milk sterilized at 120° C. 

 and this was then inoculated with a few drops of an emulsion of spores 

 of Tyrothrix tenuis, and kept at 35° C. Another lot was similarly 

 treated, except that the emulsion of spores was previously heated to 

 100 C. to destroy the enzymes present. At the end of three months, 

 the latter sample had undergone no. change and contained 0.053 per 

 cent, of soluble nitrogen ; and in the first sample, a change commenced 

 at the end of four weeks, and progressed rapidly during the next two 

 months. At the end of that time, there was some digestion of the 

 casein, and the chemical analysis showed 0.098 per cent, of soluble 

 nitrogen. This experiment showed that not only were the diastases 



