Condensed Milk and Milk Powder 159 



Contamination with Butyric Acid Bacteria. — Frequently the 

 troublesome microbe is not a yeast, but belongs to a species of bac- 

 teria highly resistent to heat, and which fail to be destroyed by 

 heating the milk to the boiling point. In this case, the contamination 

 usually originates on the farm. Organisms of this kind, which infest 

 the milk on the farm in this connection, largely belong to the butyric 

 acid group. The most prominent among them are Granulobacillus 

 saccharo-butyricus mobilis or Bacillus saccharo'butyricus, Bacillus 

 esterificans, Bacillus dimorphobutyricus. The putrefactive forms 

 of butyric acid organisms, such as Bacillus putrificus, Plectridium 

 foetidum, Plectridium novum, etc., do not seem to thrive in sweet- 

 ened condensed milk. 



The contamination may occur from dust of hay and other 

 fodder, grain, bedding, or the unclean coat of the udder and sur- 

 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 har- 

 vested 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 contam- 

 ination, unless special precautions are observed. 



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 undesirable germs and contaminate the 



