210 SWEETENED CONDENSED MILK 



rounding portions of the animal, or from milking with wet and 

 unclean hands, or from remnants of milk in unclean utensils. 



It is noticeable that the great majority of cases of blown 

 milk appear during late summer and early fall, when the crops 

 are harvested and the air in the barn is frequently loaded with 

 dust from the incoming crops. Gelatin plates exposed in the 

 stable before and during the filling of silos showed an enormous 

 increase of colonies on the plates exposed during the filling of the 

 silos. Milk drawn under such conditions is naturally subjected 

 to excessive contamination, unless special precautions are ob- 

 served. 



A very common source of these butyric acid organisms also 

 is remnants of milk in pails, strainers, coolers, cans and any 

 other utensils with which the milk may come in contact, also 

 polluted water used for rinsing the utensils. The cheese-cloth 

 strainer, owing to the fact that it is difficult to thoroughly clean 

 and that it is very seldom really clean, is a very serious menace in 

 this respect. Under average farm conditions, unless a new cloth 

 strainer is used at each milking, it is safe to condemn it entirely 

 and to recommend the use of a fine wire mesh strainer containing 

 about eighty meshes to the inch. On some farms the milk is 

 held in a set of old cans which are kept on the farm and which 

 never reach the can washer at the factory. Just before hauling 

 time these cans are emptied into the clean cans from the factory. 

 These old cans are often not washed properly and sometimes not 

 at all. The remnants of milk in these cans breed these undesir- 

 able germs and contaminate the fresh milk. It is obvious that 

 such a practice is bound to jeopardize the quality and life of the 

 finished product and may constitute a continuous cause of blown 

 milk. 



Effect of Amount of Sucrose. Since the sucrose contained 

 in sweetened condensed milk is the chief agent preserving it, 

 it is obvious that enough of it must be added to insure adequate 

 preservative action. Experience has shown that about 39 to 40 

 per cent, of sucrose is required to preserve the condensed milk 

 under average conditions. A higher per cent, of sucrose would 

 naturally intensify the preservative action and inhibit the growth 

 of the bacteria normally present more completely ; but if enough 

 sugar were added to also inhibit the growth of and make harm- 



