4l8 MICROBIOLOGY OP MILK AND MILK PRODUCTS 



rapidly than large ones, because the proportion of the mass of butter 

 exposed to the air is relatively greater. Exposure to light is also 

 claimed to exert a harmful influence. Antiseptic substances such as 

 borax and boric acid have a marked effect on the deterioration changes. 

 The New Zealand and Australian butter exported to the Enghsh mar- 

 kets is treated vdth preservatives. 



A large amount of experimental work has been done in order to 

 determine the effect of specific organisms on the keeping quality of 

 butter. The results obtained have not been definite and it is not certain i 

 that the organisms employed are constantly concerned in the deteriora- 

 tion changes. It is very probable that both bacteria and molds exert 

 an influence. The chemical changes that take place in the spoiling of 

 butter are no better known than are the causal factors.. It has been 

 asserted that there is a decomposition of the glycerides with a resulting 

 increase in free acids. It has been shown that this does not always 

 occur; that a butter may be in an advanced state of decomposition and 

 its content in volatile acids not be higher than when fresh. Two types 

 of changes are usually distinguished, rancidity and the appearance of a 

 tallow-like odor. The latter may, be due to purely chemical factors, 

 while the former is qviite certainly biological. 



Moldy butter is a frequent trouble encountered by the butter-maker. 

 If the butter is not salted, molds may develop just below the surface. 

 The most usual form of mold to appear is one with black hyphae; the 

 slightest development of which will be evident on the butter. In the 

 case of salted butter, mold on the butter itself is very rare, due appar- 

 ently to the concentration of the brine in the butter. The parchment 

 paper in which print butter is wrapped and with which the butter con- 

 tainers are lined is an excellent substratum for mold growth. . If the 

 papers and containers are badly contaminated with mold spores, or 

 they have been kept under such conditions as to permit of a limited 

 amount of growth before they are used, the development of the mold on 

 the paper after it is brought into contact with the butter is likely to be 

 rapid, even at low temperatures, and the butter is likely to reach the 

 market in an objectionable condition. The paper may be rendered 

 free from molds by placing it in water which has been heated to at least 

 80°. Butter tubs are scalded, steamed, or soaked in brine or treated 

 with a dilute solution of formaUn in order to destroy the mold spores 

 that may be present. The most efficient manner of preventing trouble 



