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: 



(1) 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: 



(1) Always make tests in duplicate. 



(2) Make sure that the sample 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. 



