174 MILK AND DAIRY PRODUCTS PART 



test is made by allowing the fat which has been melted at 

 20 C. to slowly crystallise. Characteristic spherical aggregates 

 of crystals are formed, and these give a peculiar marbled 

 appearance to the fat. When the sample only contains a little 

 cocoa-nut fat, it is best to make the test with an alcoholic extract 

 of the fat. 



A. Mercier 1 also recommends a test based upon the same 

 lines. To 1 c.c. of melted fat are added 30 c.c. of 90/ alcohol 

 and digested for five minutes at 50-55 C. Then the fat and 

 alcohol are well mixed, allowed to stand for 15-20 minutes and 

 20 c.c. decanted into a test-tube. After cooling to 30-40 and 

 filtering, the fat is allowed to slowly crystallise out. The 

 crystals are then filtered off and examined microscopically. 

 Cocoa-nut fat is shown by little bunches of crystals resembling 

 a powder puff, the individual crystals being long needles. 



In some cases the adulteration of butter with cocoa-nut oil 

 can be proved by an examination of the fat under the polarising 

 microscope. Butter fat that has been allowed to cool very 

 slowly then crystallises in spherical crystals which appear to 

 have a dark cross on them. Cocoa-nut fat, on the other hand, 

 crystallises, as has been mentioned, in long fine needles which 

 are uniformly illuminated under the polarising microscope. In 

 most cases the adulteration has been so skilfully done that the 

 characteristic shape of the fat has been purposely destroyed by 

 rapid cooling and subsequent agitation. 



Adulteration of butter with other animal or vegetable fats 

 than margarine or cocoa-nut oil also occurs, but at the present 

 time there are hardly any satisfactory analytical methods for 

 their detection, and where the falsification has been cleverly 

 done it is almost impossible to devise a means of detecting it. 



The whole of this branch of the subject contains problems 

 which are very difficult of solution by the analyst. At first 

 it was thought that by adopting a certain standard for 

 butter it would be possible to regard as adulterated those 

 samples that did not fall within the limits of this standard. 

 As the analytical material increased, however, the necessity 

 of modifying the standards arose, for often a natural butter 

 quite free from foreign fat was shown to have a composition 



1 Bull, du Service de Surveillance de la Fabr. et du Commerce des Denrees 

 alimentaires, 1904, p. 873. 



