45 6 



MICROBIOLOGY OF MILK AND MILK PRODUCTS 



taining the animal heat with the least possible exposure to the air, 

 tightly sealed at once and plunged into ice water. Such milk contains 

 no suggestion of animal odor. Aeration may be of value in removing 

 undesirable odors from milk which is not produced under good 

 sanitary conditions, if done in an atmosphere free from all dust and 

 odors, but it is not necessary for milk of good quality. The common 

 belief that aeration is valuable is probably due to the fact that most 

 aerators are coolers as well, and the beneficial results are due to the 

 cooling and not the aeration. 



CENTRIFUGAL SEPARATION. It is a common practice in some milk 

 plants to pass the milk through a centrifugal separator or clarifier to 

 remove any dirt which it may contain. This operation is effective 

 for the removal of much of the insoluble dirt which may be in the milk, 

 but it is of doubtful value from the standpoint of the bacterial content 

 and the keeping quality of the milk. In spite of the fact that the 

 separator slime is very rich in bacteria, the milk and cream as they 

 come from the machine will normally show larger bacterial counts in 

 agar and gelatin plates than will the milk before treatment, due of 

 course to the breaking up of the bacterial groups. In some cases, 

 however, there is an apparent decrease. The usual effect upon the 

 germ content of passing milk through a separator or clarifier may be 

 seen in the following tables : 



INFLUENCE OF PASSING MILK THROUGH A CENTRIFUGAL SEPARATOR UPON THE 

 GERM CONTENT OF THE SKIM MILK AND CREAM 



EFFECT OF A CENTRIFUGAL CLARIFIER UPON THE GERM CONTENT OF MILK 



