TESTS USED IN CHEESE-MAKING 425 



Composite samples. — In order to avoid testing 

 milk daily, composite samples may be prepared and 

 tested at intervals of a week or ten days. Much care 

 must be used in preparing and keeping composite 

 samples (Testing Milk, etc., pp. 24-31). 



Method of operating the test. — (Testing Milk 

 etc., pp. 53-66). In brief outline, the different 

 steps are given as follows : 



(i) Mix thoroughly sample of milk, which is at 

 60° to 70° F. 



(2) Quickly fill pipette to mark with milk. 



(3) Run milk into test-bottle. 



(4) Fill acid-measure to mark with acid and pour 

 into test-bottle. 



(5) (a) Mix milk and acid thoroughly by rotary 

 motion; (b) let stand 2 to 5 minutes; and (c) mix 

 again. 



(6) Put test-bottles in tester (centrifuge) and 

 whirl 4 or 5 minutes at proper speed. 



(7) (a) Add fairly hot water up to neck of bot- 

 tles; (b) whirl one minute; (c) add hot water to 

 8 or 9 per cent mark; and (d) whirl one minute. 



(8) Read results at temperature of about 130° F. 



Special precautions. — The following statements 

 give an outline of the particular points to be observed 

 in making the test in order to insure accuracy: 



(i) Always make tests in duplicate. 



(2) Make sure that the saniple is a representative 

 one. 



(3) Have the temperature of the milk and acid at 

 60° to 70° F. before putting in test-bottle. 



(4) Use only acid of right strength. 



