RELATION OF MICROORGANISMS TO CHEESE 501 



amount is made in Wisconsin, Ohio and New York. It is characterized 

 by its sweetish flavor and by the so-called "eyes," which are holes 

 formed by gas, produced in a fermentation that occurs subsequent to 

 the fermentation of the lactose (Fig. 149). The number of eyes is not 

 large and they are evenly distributed throughout the mass of the cheese 

 except near the surface. 



The cheese is made from as fresh milk as it is possible to secure. 

 The rennet used is prepared by placing a piece of the dried rennet in 

 whey and incubating the same for twenty-four to thirty-six hours at 30. 

 This is employed in place of the commercial extract used by the Cheddar 

 maker. It serves not only to curdle the milk, but adds to it a large 

 number of acid-forming bacteria that have grown in the rennet solution 

 during the period of incubation. The number is not, however, suffi- 

 cient to cause any development of acid during the making process which 

 differs from the preparation of Cheddar cheese in the method of firming 

 the curd. This is accomplished by heating the curd to 52 to" 1 60, and 

 by cutting it into pieces scarcely larger than grains of wheat. The salt 

 is applied to the exterior of the cheese by immersion in brine for one to 

 four days and by sprinkling salt on the surface. 



The fermentation of the lactose proceeds rapidly during the pressing 

 and subsequent thereto, so that within a few days the sugar has disap- 

 peared. The lack of the development of acid during the making probably 

 results in a somewhat different relation between the acid and protein 

 from that existing in a Cheddar cheese, which, together with the ab- 

 sence of salt gives a somewhat different environment, thus making possi- 

 ble the development of a different flora. There is no ground for believing 

 that the agents concerned in the proteoly tic changes are other than those 

 that function in Cheddar cheese. The flavor must, however, be due to 

 other factors; this is indicated by the fact that if the milk is ripened 

 as in the Cheddar process, or if salt is added to the curd the flavor will 

 approximate the Cheddar flavor. The formation of the eyes is inhib- 

 ited by salt, as is indicated by their relative scarcity in the outer layers 

 of the cheese. Jensen has shown that the eyes are due to the fermenta- 

 tion of lactates with the formation of propionic and acetic acids, and 

 carbon dioxide. The causal organism is found in the milk and the whey 

 rennet. It is believed that lactic bacteria of the Bad. bulgaricum group 

 are important factors in the ripening of Swiss cheese. They are pre- 

 sent in large numbers in the rennet and cheese. Mixed cultures of an 



