650 TESTING BUTTER 



10. The speed of the entire test will much depend on the 

 proper planning and organizing of the work of both the moisture 

 and the salt test, so as to avoid any waiting between steps, such as 

 waiting for the evaporating dish to cool, or for the fat to rise to 

 the surface in the tester. It has been found that the maximum 

 speed is obtained by running the moisture and the salt tests of three 

 samples together. 



11. Use only evaporating dishes without lips. 



Determination of Curd. 



Casein, Ash and Chlorin. Official. Cover the crucible, con- 

 taining the residue from the fat determination by the indirect 

 method, see official fat determination, and heat gently at first, then 

 raise the temperature gradually to just below redness. The cover 

 may then be removed and heating continued until the contents of 

 the crucible are white. The loss in weight represents casein, and 

 the residue in the crucible, mineral water. Dissolve this mineral 

 matter in water slightly acidified with nitric acid and determine 

 chlorin, either gravimetrically or volumetrically. 



The curd or casein content of butter as determined by the Offi- 

 cial Method includes the lactose also. Since normal butter contains 

 approximately .3 per cent lactose, the nitrogenous curd content of 

 butter is in reality about .3 per cent lower than the per cent curd as 

 determined by the Official Method. 



For making an exact determination of curd, in contradistinction 

 to the curd determination, as the term is used in the Official Method, 

 the following method is recommended : l 



Dry about 10 grams of butter in a flat-bottom porcelain evap- 

 orating dish in a steam drying oven at about 98 to 99 degrees C. 

 Remove the fat by dissolving with petroleum ether and filter, trans- 

 ferring the entire contents of the evaporating dish to the filter, and 

 rinsing with petroleum ether. Transfer filter paper and contents 

 to a Kjeldahl flask and determine the nitrogen by the Kjeldahl 

 method, using the factor 6.38 in calculating the per cent of protein 

 or curd. 



The United States Bureau of Chemistry 2 recommends the same 

 method but suggests the use of a 25 gram sample. 



1 Hunziker, Spitzer and Mills, The Pasteurization of Sour, Farm-Skimmed 

 Cream for Butter Making. Purdue Bulletin 203, 1917. 



2 United States Bureau of Chemistry, Information by Correspondence, 

 March, 1919. 



