370 STATE BOARD OF AGRICULTURE. 



PREVIOUS WORK. 



The two most vitally important questions concerning the rancidity of 

 butter are: first, What compounds cause the rancid taste and smell? and 

 second, How are they produced in butter? The first question is not yet 

 satisfactorily answered, and therefore, of course, the second cannot be 

 answered completely. 



The original idea, the simplest, was that in some way the fat was 

 split into glycerine and free acids and that these, especially the butyric 

 and capronic acids, cause the rancid taste. The observation that butter 

 protected from air kept better, led to the theory that oxidation, also, must 

 have something to do with rancidity. With this latter thought Schmidt 

 and Schaffer attempted to correlate the progress of rancidity and the in- 

 crease in aldehyde, but found them apparently unrelated. Amthor considered 

 ethyl butyrate a factor concerned with the rancid smell and odor. This, 

 he thought, was produced by a reaction of butyric acid with the alcohol 

 produced from fermentation of the lactose. 



Jensen notes that the volatile saponifiab.e svibstances in rancid butter 

 arise not alone from the esters of the volatile fatty acids, as shown by the 

 difficult saponifiability of a part of them, and the fact that the amount of 

 these substances is not always in proportion to the rancidity of the butter. 

 It is clear that the palatability of a fat does not necessarily depend upon 

 the content of free fatty acid, since only these acids or esters which are 

 volatile, or soluble in water, affect the sense of taste. Reinmann (1. c, p. 212) 

 noticed in one sample a rise of 19.5 degrees of acidity wthout any rancidity, 

 while another sample became very rancid v^ith an increase of only 10.0 

 degrees. Therefore, the more or less strong odor of ester which a butter 

 develops is not always in proportion to the determined amount of volatile, 

 saponifiable substances. 



Duclaux showed that aroma and color were destroyed by contact with 

 the air in the presence of light, and that the butter became tallowy and 

 white. He hastened this reaction by absorbing the butter by means of 

 pumice stone, and determined the absorption of oxygen and formation of 

 CO 2. This oxidation of the butter caused a distinct increase in its weight, 

 which was considerably higher in the case of olein and oleic acid than of 

 butter fat, as would be expected. 



Ritsert isolated various micro-organisms, chiefly yeasts and oidium 

 molds from old, rancid fat, and inoculated these into fresh, undecomposed 

 fat, in order to determine if they might render this rancid also, but found 

 that the micro-organisms would not develop in the fresh fat, and therefore 

 could not cause rancidity. It is for this reason that perfectly pure lard or 

 tallow may be Ivept for so long in a fresh condition if protected from light. 



Jensen placed samples of butter in glass tubes which, both unsterilized 

 and sterile, he exposed to sunlight, diffused light, and darkness, at tem- 

 peratures of 35° and 20 °C. After periods of from one to ten weeks he de- 

 termined the amount and nature of the changes effected by means of the 

 senses of taste and smell, the rise in acidity or aldehyde and the decrease 

 in the iodine number. He also counted the organisms present. The results 

 of this work may be summed up as follows: 



