4 BULLETIN 944, U. S. DEPARTMENT OF AGRICULTURE. 



EXPERIMENTS AT GROVE CITY CREAMERY. 



COMPARISON OF ACIDITY AND ALCOHOL TESTS OF MILK FOR CONDENSING. 



Finding no consistent relation between the coagulation of milk 

 by alcohol and its acidity content as shown by the titration method, 

 work was started to ascertain the relative value of the two tests. 

 Samples of milk, representing all conditions met with at the con- 

 densery, were taken at the weigh room of the Grove City creamery. 

 Five pounds of each sample selected — which in the large majority 

 of cases represented a mixed milk of some particular patron's herd — 

 was evaporated in a 10-liter flask under a vacuum of 25 to 27 inches 

 to a concentration of 2| to 1, the time required being from 50 to 70 

 minutes, with a temperature of 40° to 50° C. (104° to 122° F.) . The 

 evaporated milk was placed in baby-size tins and sterilized in an 

 autoclave for 30-minute intervals at 121.1°, 112.8°, and 107.2° C. 

 (250°, 235°, and 225° F.). Portions of evaporated milk in 100 c. c. 

 Erlenmeyer flasks were run in the autoclave at the temperatures used 

 and also at 100° C. (212° F.) for 30 minutes to note the extent of 

 coagulation. When sterilization at 112.8° C. (235° F.) for 30 

 minutes indicated that the product would not stand a higher process- 

 ing, the next lower temperature was used, only two temperatures 

 higher than 100° C. (212° F.) being used. The cooled cans of steri- 

 lized milk were shaken for one minute before examination for gen- 

 eral physical appearance and curdiness. 



The main observation of the sterilized samples of evaporated milk 

 concerned the extent of coagulation and whether or not they showed 

 curdiness after shaking. Curdiness of shaken samples was de- 

 termined by the physical appearance of the product and by mixing 

 a portion of it with hot water. In reporting on whether or not the 

 sterilized samples were curdy after shaking, the temperature of 

 112.8° C. (235° F.) for 30 minutes was used as a standard of compari- 

 son. In the large majority of instances the curdiness was pronounced 

 enough to leave no doubt as to the accuracy of decision, and the 

 sample sterilized at the lower temperature quite generally substan- 

 tiated the classification given on the basis of the standard tempera- 

 ture used. On the other hand, the samples showing no curdiness 

 after sterilization were in most cases not at all difficult to classify, as 

 they showed, in general, less coagulation even with the higher 

 temperature. 



Table 1 shows the results of sterilization of 90 samples of milk of 

 varying acidity, 45 of which coagulated with '75 per cent alcohol. 

 Forty-three of the 45 when evaporated and sterilized at 112.8° C. 

 (235° F.) for 30 minutes showed curdiness after shaking. Coagula- 

 tion of practically all these samples when evaporated was very pro- 

 nounced, in some instances being so hard that it was impossible in 





