v DECOMPOSITION PRODUCTS 229 



leucine, tyrosine, phenol, indol, skatol, &c., the reader is 

 referred to text-books on organic chemistry, for the methods 

 are only exceptionally earned out in practical analytical 

 laboratories. 



II. DECOMPOSITION PRODUCTS OF BUTTER. 



The normal spontaneous decomposition of butter is seen in 

 every day life when butter turns rancid. This process consists 

 in the continued splitting up of the glycerides of the butter 

 into glycerine and free fatty acids. These free fatty acids, the 

 volatile ones, and particularly butyric acid, impart the objec- 

 tionable rancid taste and smell. This hydrolytic cleavage is 

 caused by certain micro-organisms, and the part which they 

 play in turning butter rancid has been proved by Orla 

 Jensen. 1 The most important of these micro-organisms are 

 the following : O'idium laetis, Cladosporium butyri (both of 

 which are moulds), also Bacillus fluorescens liquefaciens, and less 

 often Bacterium prodigiosum. 



O'idium lactis, Bacillus fluorescens liquefaciens, and Bacterium 

 prodigiosum can only split up the fat, and are not able to attack 

 the combined glycerine, They split up the butter fat without 

 the formation of esters. Cladosporium butyri and Penicilliuni 

 glaucum not only split up the fat, but also attack the glycerine. 

 They split up the butter fat with the formation of transitory 

 esters. Finally, certain varieties of mycoderma have not the 

 power to split up the fat, but they can attack the combined 

 glycerine. They form only esters. Amongst the esters the 

 first place is taken by ethyl butyrate, and its importance in the 

 taste and smell of rancid butter has been investigated by 

 Amthor. 2 



In this way butter undergoes total decomposition due to the 

 large number of micro-organisms (many millions per gram 

 immediately after the butter has been made) and to the 

 quantity of food in the form of casein, milk sugar, and salts 

 which is at their disposal. The larger the amount of such 

 substances in the butter the more rapid is the decomposition. 



1 " Studien iiber das Ranzigwerden der Butter," Landwirtxchaftlichzs 

 Jahrbuch der Schweiz, 1901. 



2 Zeitschriftffir analytische Chemie, 1899, p. 10. 



