86 MODERN METHODS OF TESTING MILK 



after which it is vigorously and continuously shaken 

 until cooled to 60 F. or lower, and then the sample is 

 taken and weighed as quickly as possible. Agitation 

 during the process of cooling is essential to keep the 

 melted fat from separating so rapidly as to prevent 

 obtaining a uniform mixture. 



WHY USE OF PIPETTE IS INACCURATE FOR 

 CREAM 



The use of a pipette for measuring cream samples 

 is inaccurate for the following reasons : ( i ) More fat 

 adheres to the inside of a pipette than in case of 



milk, the er- 

 ror increas- 

 ing with the 

 thickness of cream. (2) 

 The weight of cream de- 

 creases as the per cent, of 

 fat in cream increases, 

 FIG. 33 since milk- fat is lighter 



CREAM-SAMPLING SIEVE ,, ,, ,, ... 



than the other constituents 



of cream. The scale of the test-bottle is based on the 

 use of 1 8 grams of material, but the amount of cream 

 that occupies the volume filled by 18 grams of milk 

 (17.5 cc.) is found to be more or less below 18 grams 

 according to the increased percentage of fat in the 

 cream, running even below 17 grams in very rich 

 cream. (3) Separator cream is more or less filled with 

 bubbles of air, and ripened cream contains gases pro- 

 duced by fermentation. These decrease the weight of 

 a given volume of cream. 



For the preceding reasons, the result of trying to 



