144 Dairy Bacteriology. 



In rancid butter, butyric and allied acids are always 

 found, and it was supposed for a long time that the 

 change was a butyric fermentation inaugurated by some 

 of the butyric organisms that are found so commonly 

 in milk and cream. 



Ritsert 1 found that sterile butter became rancid in three 

 days if exposed to the action of the light, while unsteril- 

 ized, normal butter exposed under similar conditions, did 

 not change in five months, if the air was excluded from 

 it. Duclaux 2 has proven that the rancid change is largely 

 a chemical action that takes place in butter-fat where it 

 is exposed to light and oxygen; that it is not necessarily 

 inaugurated by the vital functions of any special kind of 

 bacteria. While the change goes on in most cases in a 

 purely chemical way, there are, however, certain organ- 

 isms that are able to hasten this process if they are 

 present in the butter 3 . For this reason a soft butter 

 containing considerable quantities of buttermilk, and 

 therefore rich in nitrogenous material, undergoes a rapid 

 change and quickly becomes rancid. 



145. Defects due to manufacturing' methods. 

 There are other defects in butter that are also attributa- 

 ble to other than bacterial causes. These are for the most 

 part due to errors in manufacture. Thus, mottled or 

 wavy butter is generally caused by the uneven distribu- 

 tion of the salt. White specks in butter are often pro- 

 duced where the cream is allowed to ripen for too long a 

 time, or where curdled milk is used as a starter. In such 

 cases, the curd particles remain undissolved, and are held 

 in the butter, where they appear as white specks. 



1 Ritsert, Inaug. Diss. Berne, 1890. 



* Duclaux, Le Lait, p. 34. 



3 Von Klecki, Cent. f. Bakt., 15: 354. 



