14 DAIRY LABORATORY GUIDE 



EXERCISE 4 



THE PURITY OF MARKET MILK AND CREAM 



Object: To determine the purity of market milk and 

 cream with reference to the amount of suspended dirt present. 



Apparatus: Samples of milk, cream, and skimmilk; sedi- 

 ment tester; and pint jars. 



FILTER METHOD 



Steps : 1. Secure a pint of unstrained milk from a com- 

 mon milk pail, and filter. Remove the cotton disks and dry 

 on blotting paper or on a warm surface. Examine with a 

 reading glass and record the findings. 



2. Secure a sample of milk from a small-top milk pail to 

 test its sanitary efficiency. 



3. Test the efficiency of different kinds of strainers by 

 filtering samples of milk after straining through an ordinary 

 wire strainer, a cotton strainer, or a cheesecloth strainer. 



Fig. 1. Sediment tester. 



4. Test the efficiency of a hand separator in removing 

 suspended dirt by filtering a pint of milk before separating; 

 then filtering samples of the cream and the skimmilk after 

 separation. 



GRAVITY METHOD 



Steps : 1. After stirring the milk well, take samples and 

 put into covered glass cylinders or bottles and set aside 

 undisturbed for a short time. 



2. To examine, raise the cylinder carefully to a position 

 even with the eye; then look for sediment in the bottom, 



