216 ANNUAL, REPORTS OF DEPARTMENT OF AGRICULTURE. 



NUTKITION AND MILK SECBETION. 



In previously reported nutrition experiments it was found that 

 certain minerals taken in the feed had a marked effect on the milk 

 flow and condition of the dairy cow. Further experiments have been 

 carried on to determine whether the effect of feeding calcium carbo- 

 nate is caused specifically by the calcium or by the changing of the 

 acid-base balance. Sodium carbonate was substituted for the calcium 

 carbonate, and the results show that sodium carbonate had no effect 

 on milk yield when added to a timothy-hay ration, whereas the cal- 

 cium carbonate did affect the yield perceptibly. In an experiment 

 where the cow was fed a ration varying in diet protein, it was found 

 that the diet protein may effect changes in the composition of the 

 milk. 



BACTERIOLOGY AND CHEMISTRY OF MILK. 



Further studies were made of the characteristics and identity of 

 certain species of streptococci that are found in milk and some of 

 which are also found in the mouths and in the feces of cows. A study 

 of the milk-souring streptococci has been completed. 



A harmless organism which grows rapidly during the pasteurizing 

 process and which has been termed Lactobacillus thermo'philus has 

 been found to be a cause of so-called " pin-point " colonies on culture 

 plates from pasteurized milk. The presence of this organism, which 

 survives ordinary pasteurization, complicates the problem of trans- 

 porting milk in a hot condition. The organism is destroyed at a 

 temperature of 180° F. 



Considerable attention has been paid to the phenomenon of bac- 

 terial growth and several points of technical importance have been 

 established. 



In studies relating to the chemistry of milk products the relative 

 importance of moisture, acidity, and light in the oxidation of but- 

 terfat was determined, and the condition known as tallowiness in 

 butterfat was found to be due to oxidation by-products, though th& 

 mechanism of the reaction has not been fully determined. Pure 

 butterfat of excellent keeping quality has been prepared from fresh 

 butterfat by thorough washing of the fat and also by controlled 

 steam distillation. 



MANUFACTURE OF MILK PRODUCTS. 



Condensed milk. — In the process of condensing and evaporating 

 milk it is necessary that milk be forewarmed before it is drawn into 

 the vacuum pan. Experiments by the Dairy Division during the year 

 show that the temperature of f orewarming has a marked effect on the 

 coagulation of the finished condensed product. In the case of the 

 unsweetened evaporated milk it was found that the best forewarming 

 temperature was between 95° and 100° C. Sweetened condensed milk 

 gave the best results when the forewarming temperature was between. 

 55° and 65° C. Wlien the raw milk was forewarmed at other tem- 

 peratures there was a tendency for the milk to coagulate in the can 

 upon storage in the case of condensed milk or during the sterilizing 

 process in the case of evaporated milk. 



