RIPENING PROCESSES OF CHEESES 149 



ripening. The cultures may also be obtained in powder form 

 for sprinkling on the cheeses 1 . 



Only the acid curd cheeses remain to be discussed. These include 

 both hard and soft varieties, and the latter include both smeared 

 and mouldy cheeses even cheeses which resemble Roquefort in 

 being permeated with moulds, e.g., the Norwegian Gammelost. 

 The making of the hard acid curd cheeses 2 , the Danish cheeses, 

 Appetitost, Knapost, the Norwegian Pultost, and the Swiss Green 

 Alpine Cheese (Schabzeiger) presents several points of interest; they 

 are scalded at a high temperature or for a long time and ripened 

 before they are shaped (the Norwegian Pultost is not shaped at 

 all). The scalding produces the same results as in the pasteurisa- 

 tion of milk : the development of the sporing bacteria and the 

 suppression of the lactic acid bacteria ; as the author has shown 

 in the case of Schabzeiger 3 , and v. Klecki in the case of another 

 acid curd cheese 4 , the curd develops a vigorous butyric acid 

 fermentation ; in both cases the butyric acid bacteria were motile ; 

 the butyric acid gives these cheeses a sharp taste. The ripening 

 proper is due to lactic acid rod bacteria, which possibly act in 

 conjunction with other microorganisms. As regards the decompo- 

 sition undergone by the casein, the hard acid curd cheeses do not 

 differ greatly from the hard rennet curd cheeses (see table, 

 p. 133). According to Olav Johan-Olsen 5 , the ripening of Pultost, 

 in which the author has found a fair amount of valerianic acid, is 

 accomplished by yeast, Oidium lactis, and especially by a species 

 of Mucor. Johan-Olsen has also carried out a detailed investi- 

 gation of the ripening of the Norwegian Gammelost. Here the 

 active moulds are especially species of Penicillium and Mucor, 

 which turn the cheese green and brown respectively. As the curd 

 or the cheese itself is strongly heated, it is improbable that the 

 moulds are derived from the sour milk ; they must find their 

 way into the cheese at a later stage, and gradually penetrate from 

 the surface throughout the whole mass. This already takes 

 place during the first six weeks, as the curd is fairly acid and 

 porous. 



If it is desired to utilise separated milk for cheese, this is 

 best done by turning it into one of the above-mentioned acid 



1 According to our experience, it is sufficient to infect the mats with 

 P. Candidum. The bacteria come of their own accord while the Oidia 

 only do harm, 



2 Several of these cheeses contain, in addition to casein, smaller or larger 

 amounts of albumin (Zeiger), which ajso has an influence on the ripening 

 process. 



3 " Centralblatt f. Bakt.," 2 Abt,, 1904, Bd. XIII., p. 755, and 1907. 

 Bd. XVII., p. 225. 



* "Centralblatt f. Bakt.," 2 Abt., 1896, Bd. II., p. 169. 



5 " Undersogelser over Ost og Ostegaering," Kristiania, 1905. 



