CHAP. V. 



THE TESTING OF BUTTER FAT. 



317 



subjected to identical tests, the butter from different breeds yields 

 different results. 



Holsteins gave an average viscocity of 237, ranging from 112 to 461. Samples of the 

 butter of seven pure-bred Jerseys averaged 74, ranging from 50 to 103. Breed peculiarities 

 are thus clearly indicated. The average viscocity of solutions of soaps from butter fat is 

 about 100 ; that of lard, tallow, oleomargarine, oil, and of all the commercial substitutes 

 for butter exceeds 1,000 ; hence, this test affords a valuable means of discrimination. 

 Nevertheless, owing to the great variation in the composition of butter, there is such a 

 wide range in the viscocity of the solutions of butter soaps, that it is possible to adulterate 

 the butter giving the least viscous soap as much as 30 per cent, before the higher limit for 

 butter is passed. But by combining the viscocity test with another test known as 

 Reichert's which depends upon the amount of fatty acids obtained in a specified manner 

 from 2 - 5 grams of butter fat a very trustworthy result is obtained. It may be added, 

 however, that where the viscocity number exceeds 500 there need be no doubt "whatever as 

 to adulteration ; it is the butter giving viscocities of 200 to 500 that must be regarded with 

 suspicion, which may be allayed or confirmed by applying Reichert's test. 



It appears probable that the viscocity of butter soap solutions diminishes with age. 

 Dr. Babcock tested seven samples of butter in May, shortly after churning, and again in 

 October. The following table shows the viscocity of each sample in May, and, immediately 

 below, the viscocity of the same sample in October : 



In May 



In October 



65, 69, 62, 61, 69, 98, 65 ; average 65' 

 54, 62, 62, 58, 53, 62, 54 ; average 57' 



A knowledge of viscocity is of value in indicating changes in the physical constitution of 

 milk, which are often of more importance to the dairyman than are changes in the amount 

 of solids or of fat. Changes in the size of the fat globules or in the viscocity of the milk 

 serum are of this character, but are not indicated by chemical analysis. A low viscocity of 

 the milk serum (that is, the liquid part), associated with large fat globules, favours the 

 economical production of butter. The coefficient of viscocity for the fat of milk increases 

 with the size of the globules, hence the greater the difference between the viscocity of the 

 whole milk and that of the skim-milk the more valuable will the milk be for the production 

 of butter, provided the viscocity of the skim-milk is not very high. 



A noteworthy fact is that when warm milk is rim through a centrifugal separator, and the 

 skim-milk and cream are caught in the same vessel and thoroughly mixed together again, 

 the product is less viscous than the original milk. This appears to be chiefly due to the 

 breaking up of the fat globules. The extent to which this division takes place is shown by 

 the following determination made by Dr. Babcock of the number of fat globules before and 

 after separation : 



The effect which this division of the fat globules has upon the quantity and quality of the 

 butter made from separated cream is not yet ascertained. Nevertheless, the peculiarity 

 under notice may explain why the same manipulation which produces high-grade butter 

 from ordinary cream often fails when applied to separated cream. 



In explanation of the iodine number, it may be premised that the combination of the 

 fatty acids with glycerin are called glycerides, and of these, olein, stearin, palmitin, and 

 butyrin are examples. Now, of the fatty acids found in the glycerides of butter fat, oleic 

 acid is the only one which has the property of absorbing iodine. Each molecule of the acid 

 absorbs, moreover, one molecule of iodine, so that the quantity of iodine absorbed is directly 

 proportional to the quantity of olein present. The variation in this iodine number, par- 

 ticularly in the butter from single cows, is very great, showing the percentage of olein in 

 such butters to range from 277 to 52 '1. In the New York tests the average for the 

 Holsteins was as high as 46 '19, that for the other breeds tested being 35 "4 per cent. This 

 high proportion of olein in Holstein butter may account for its softness as compared with 

 Jersey butter. The wide range of the iodine number shows olein to be undoubtedly the 



