iqoo-i.] The Ripening of Cheese. 103 



THE RIPENING OF CHEESE AND THE ROLE OF 

 MICRO-ORGANISMS IN THE PROCESS. 



F. C. Harrison, Agricultural College, Guelph. 



(Read 2^rd March, iqoi). 



During the last twenty-five years the ripening of cheese has been 

 the subject of numerous investigations, and although the problem has 

 been attacked in many varied ways, it cannot be said, even now, that 

 the changes which cheese undergoes from the time it is made until it is 

 ready to be eaten have been fully explained. 



The task of the investigator is, no doubt, a difficult one, owing to 

 the many different kinds of cheese manufactured, the various ways in 

 which they are made, and the diverse methods used to ripen them. 

 The difficulties do not by any means end here. No two cheeses are 

 exactly alike ; the bacterial flora of the milk changes constantly ; the 

 methods of manufacture differ slightly from day to day, and more so 

 from season to season ; the temperature and humidity of the curing 

 room usuall)' alter with the outside temperature ; and lastly the 

 difficulty of sampling and the methods of analysis leave much room for 

 improvement. The constant publication of some new culture method 

 for lactic acid bacteria suggests that as yet no completely satisfactory 

 method of cultivating them has been discovered. 



Ferdinand Cohn, in 1875, declared that the ripening of cheese was a 

 fermentation due to the influence of fermenting organisms. He micro- 

 scopically investigated rennet, and finding bacteria present in this 

 substance concluded that the ripening of cheese was due to bacteria 

 introduced into the cheese from this source. He considered that the 

 milk sugar underwent butyric fermentation. He also found B. termo, 

 microcci, and the Hay bacillus present in the cheese, and came to the 

 conclusion that these were introduced with the rennet, because Remak 

 had found B. subtilis in the stomachs of calves. 



A few years later Duclaux published his researches upon Cantal 

 cheese, a soft cheese manufactured in France. He isolated a number of 

 micro-organisms, six of which he supposed were of special importance, 

 — an alcoholic, a lactic, a butyric, and a ferment acting upon casein and 



