388 



MICROBIOLOGY OF MILK AND MILK PRODUCTS 



different samples is due to the nature of the dirt itself. The coarser 

 the dirt the greater the proportion that will be removed by straining. 

 It is not true, however, that the keeping quality is necessarily 

 improved by the simple process of straining. It depends largely upon 

 the condition of the milk and the nature of the strainer. Not infre- 

 quently passing milk through a strainer not only fails to improve its 

 keeping quaUty but actually injures it. This has been shown by a 

 number of investigators. The effect of straining upon the germ con- 

 tent may be seen in the following figures where the milk was passed 

 through a strainer composed of three thicknesses of fine cheese cloth 

 supported by wire gauze. 



EiTECT or Straining upon Bacteriai. Content of Mh-k 



The effect of straining upon the keeping quaUty is shown in the 

 following experiments where the milk was strained through the same 

 form of strainer mentioned above and the samples kept at constant 

 temperature of 21° until coagulation. 



It will be seen that in no case was the keeping quality of these 

 samples increased by the straining process while in some cases it 

 was materially injured. 



