140 BACTERIOLOGICAL METHODS 



1. Lactic acid bacteria. These are the chief agents concerned in the ripening of 

 Cheddar, American and Edam cheese. Pure cultures of the Bacillus acidi lactici are 

 often used as a starter. In the manufacture of the Edam cheese, slimy whey is 

 used as a starter (Streptococcus hollandicus] . 



2. Penicillium glaucum the common green mold is the principle organism con- 

 cerned in the ripening of Roquefort, Gorganzola and Brie cheeses. In some coun- 

 tries the green mold is scraped from molded bread and added to the curd. 



3. A great variety of other bacteria, yeasts and mold are concerned in the devel- 

 opment of the more specific flavors and aromas. Further investigation is necessary 

 to ascertain the special function performed by each and the mutualistic relationship 

 that may exist between them. 



4. Gas generating bacteria are concerned in the formation of holes in the interior 

 of the ripening cheese. These gas formers also modify the aroma or flavor of the 

 cheese and in some instances constitute the chief ripening agents. 



Spoiling of cheese is not uncommon, due to the invasion of a 

 variety of undesirable organisms. The cheese " hopper" or 

 "skipper" found in and upon old and overripened cheese and in 

 cheeses which have not been properly screened, is the larva of the 

 black two-winged fly Piophila casei. The insect deposits its 

 eggs in the surface cracks and crevices of the cheese upon which the 

 developing larva feeds. The name skipper or hopper is derived 

 from the fact that the larvae are capable of projecting themselves 

 some distance by coiling and suddenly uncoiling. 



This fly is a common pest in the dairying establishments. A 

 less common but even more annoying pest is the larva of the 

 "bacon beetle." Cheeses which are comparatively hard and 

 smooth externally are not so likely to be infested by the skipper 

 or bacon beetle larva as are the cheeses which are rough externally. 

 It is customary to wipe the cheese in order to remove the para- 

 sites. If the cheeses which are stored for ripening are properly 

 screened, the fly and beetle cannot get access to them to deposit 

 the eggs. A small mite (Trioglyphis siro) also occurs on cheese 

 upon which it feeds. 



Inadequately screened cheeses also permit flies and other pests 

 to deposit possible infections, thus typhoid contamination and 

 also pus streptococci and staphylococci may be found upon this 

 food substance. 



