246 Report of the Chemical Department of the 



INTRODUCTION. 



The object of this bulletin is to present the results of our study 

 relating to some of the more prominent conditions that influence 

 the chemical changes taking place in the nitrogen compounds of 

 cheese during the ripening process. It is well known that, dur- 

 ing the cheese-making process, chemical changes soon begin in 

 the freshly coagulated curd or paracasein formed when milk- 

 casein is acted upon by rennet. The same cheese examined at 

 intervals is found to show quite marked variations in the charac- 

 ter of its nitrogen compounds. Cheeses made from the same 

 milk under the same conditions of manufacture and subjected to 

 different conditions during the ripening process show a difference 

 in chemical composition. Qieeses manufactured under different 

 conditions and ripened under uniform conditions may vary in the 

 character of their nitrogen compounds. It has seemed to us 

 desirable that a somewhat comprehensive study should be made 

 of the changes actually found in the nitrogen compounds of 

 cheese, using in the work only cheeses made and ripened under 

 known, controlled conditions. The results presented in this bul- 

 letin by no means exhaust the subject, our intention being to 

 study first only some of the more prominent factors, such as time, 

 temperature, moisture, salt, rennet, acid, etc. 



The chief proteid of curd, freshly coagulated by rennet, is, 

 under usual conditions, a compound called paracasein, in some 

 respects resembling milk-casein, in other respects differing from 

 it in a marked degree. The exact chemical relation of these two 

 compounds has not yet been learned. In the usual methods of 

 cheese-making, the milk-sugar, acted on by certain organisms, 

 begins to form lactic acid early in the process and this acid, as 

 rapidly as formed, combines chemically with paracasein to form a 

 compound called paracasein monolactate. Many of the peculiar 

 properties of curd are believed to^ be due to the presence of this 

 paracasein monolactate, such as the ability to form fine strings on 

 a hot iron, the changes in appearance, plasticity and texture and, 

 perhaps, the shrinking. It is also probable that paracasein mono- 

 lactate forms the real starting point of cheese-ripening or, stated 



