2 3 



MILK AND DAIRY PRODUCTS PART 



The process of becoming rancid spreads from the outside to the 

 interior in the same way as the ripening in soft cheese. 



The extent of hydrolysis is simply determined by esti- 

 mating the amount of free acid by titration. There exists, 

 however, no definite relation between the degree of rancidity 

 and the amount of free fatty acids. 



Direct sunlight causes butter fat (like other fats) to undergo 

 another process of transformation, namely, oxidation, whereby 

 the unsaturated fatty acids in the butter, that is the oleic acid 

 principally, are attacked, as Duclaux and others have shown. 

 The glycerine is also partially attacked. The advance in the pro- 

 cess of oxidation is best measured by the iodine number, which 

 of course diminishes more and more. It is further of interest 

 to test for aldehyde, which is also formed, and which bleaches 

 the butter, and gives it at the same time a tallowy, not rancid, 

 taste. This process is distinguished from the biological decom- 

 position which results in the butter becoming rancid. The 

 difference between the two processes is shown in the following 

 table by Orla Jensen : 



1 Determination of the Degree of Rancidity. 



The extent of the hydrolytic processes going on in butter can 

 be measured, as mentioned above, by titrating the amount of 

 free acid. In this way the acid number is obtained expressed 

 as the number of cubic centimetres of normal alkali required 

 to neutralise 100 g. of fat. The method of making this deter- 

 mination has already been given on p. 156. The acid number 

 of butter does not in any way serve as a measure of those 

 products of rancidity which affect the taste and smell. 



