RIPENING PROCESSES OF CHEESES 145 



surface. The species of Penicillium found in Stilton and Gorgon- 

 zola appear to be mainly Penicillium roqueforti. This circum- 

 stance is explained by Thorn and Currie x by the fact that P. 

 roqueforti can thrive with less oxygen than the other Penicillia, 

 and therefore obtains predominance in the interior of the cheese, 

 even though the cheese has not been inoculated with it. In the 

 making of Roquefort cheese the veins are produced where desired 

 by dusting with mouldy bread, of which about 0-1 per cent, of the 

 weight of the cheese is used ; the mould grows not only in these 

 places, but also in the holes made by the needle ; it is able to 

 overgrow the cheese bacteria owing to the low temperature (8 C.) 

 at which the cheese is ripened. The bread used for the cultivation 

 of the mould is best made from a dough containing equal parts of 

 rye, barley and wheat flour, and a little lactic or acetic acid, in which 

 acid fermentation is induced by the addition of some sour dough. 

 The bread is very thoroughly baked, which, in conjunction with the 

 action of the acid which has been added, destroys bacterial spores 

 which otherwise would develop when the bread is set aside for the 

 development of the moulds. It is then cut into slices and dipped 

 into sterile water containing J per cent, of acetic acid, into which 

 a culture of the mould has been stirred. The bread slices are 

 placed close together on sterile shelves in a damp room and 

 covered with sterile filter paper. As the change in temperature 

 caused by the growth of the mould, when this sets in, is consider- 

 able, the initial temperature should be kept down to 9 to 10 C. 

 When in the course of three to four weeks the bread has become 

 thoroughly mouldy, the crusts are removed and the slices are 

 dried for about ten days at 30 to 32 C., after which they are ready 

 to be ground and sifted. The yield is 45 per cent, of the original 

 weight of the bread. 



Even if the work is carried out in rooms which are as sterile as 

 possible, it is difficult to avoid infection with foreign moulds. 

 The author has accordingly worked out a method 2 in which the 

 strain of P. roqueforti which is used is little by little accustomed 

 to stand comparatively large amounts of formaldehyde. Formalin 

 can be added to the water in which the slices are dipped, whereby 

 the development of the foreign moulds which cannot stand 

 formalin is inhibited. A mould powder made in this way is sold 

 by Messrs. Blauenfeldt and Tvede, of Copenhagen. 



As already mentioned, the ripening process of the soft rennet curd 

 cheeses starts at the surface and works inwards. At the same time, 

 a ripening action due to the rennet takes place throughout the whole 

 mass, even though it may not be very obvious. While the amounts 



1 " Journal of Biol. Chem.," 1913, vol. 15, pp. 249 and 259. 



2 " Maelkeritidende," 1919, p. 277. 



P.B. 10 



