376 CHEESE 



Pour off the whey, cover up, and leave for an hour ; then 

 note odour again, and pour off any whey still left. 



Repeat observation every two hours. 



After eight or twelve hours, take out the curd from each and 

 cut it in two with a sharp knife. 



Note the presence or absence of oval or round bubbles, or 

 pin-holes, and the odour of the curd. 



Large holes of irregular shape are due to want of close packing 

 of the curd after being cut. 



Ex. 163. Inoculate two tubes of whey-gelatine with Bact. 

 lactis aerogeneS) or other organism isolated from spongy curd. 



Incubate one of them at 22 C. ; keep the other in a cool 

 place at 15 C. or lower. 



Note after twenty-four to twenty-eight hours the presence or 

 absence of gas bubbles in each. 



Ex. 164. Take two tubes of whey-gelatine; to one of them 

 add . i per cent, of potassium nitrate. 



Now inoculate both with Bact. lactis aerogenes or similar gas- 

 producing organism. 



Inoculate at 22 C. 



Do colonies appear equally in both tubes ? 



In which are gas bubbles most abundant ? 



Test both at intervals of six hours for nitrites by method 

 described in Ex. 74. 



(ii) Bitter Cheese. The production of bitterness in 

 cheese is usually due to the work of micro-organisms. 



The putrefactive bacteria may cause this trouble to 

 arise, and some of the organisms noted as being respon- 

 sible for bitterness in milk (p. 283) have been found to 

 induce the objectionable flavour in cheese, although 

 bitter milk does not necessarily make bitter cheese. 



Freudenreich's Micrococcus casei amari was found to 

 be one of the causes of the development of the objection- 

 able flavour in Emmenthal cheese. 



