THE ALCOHOL TEST IN" RELATION TO MILK. 



the acidity had increased from 1.98 to 2.14, and the bacteria from 

 from 82,000 to 15,100,000 per cubic centimeter. It is interesting to 

 note that an extensive multiplication of lactic-acid-forming bacteria 

 may occur without causing a positive alcohol test. In the second 

 experiment, also shown in Table 4, a heavier inoculation was used, and 

 it will be seen that the milk at the beginning of the incubation period 

 contained 480,000 bacteria per cubic centimeter. The 68 per cent 

 alcohol test was not positive until the bacteria had increased to 

 31,400,000 per cubic centimeter. 



These figures show that when a pure culture of lactic-acid-forming 

 bacteria is grown in s k im milk there must be a very great increase in 

 order to produce acidity enough to cause a positive alcohol test. In 

 these experiments there were no positive alcohol tests until the bac- 

 teria had increased from less than 500,000 to over 16,000,000 per cubic 

 centimeter. From these results it is apparent that the growth of 

 acid-forming bacteria in milk may, through the formation of acid, 

 cause a positive alcohol test. However, when there is sufficient acid 

 produced to cause a coagulation with 68 per cent alcohol the number 

 of acid-formmg bacteria would be very high. 



Table 4. 



-Influence on the alcohol test of acid produced by the growth of a pure culture of 

 lactic-acid bacteria. 



Experi- 

 ment No. 



Age of 

 culture 

 in hours. 



Bacteria 

 per cubic 



centimeter. 



Acidity. 



Alcohol test. 



75 per cent. 



68 per cent. 



44 per cent. 



I 

 II 





 2 

 4 

 5 

 6 

 7 

 

 2 

 4 

 5 

 6 

 7 



82,000 



113,000 



1,510,000 



4,300,000 



11,700,000 



15,100,000 



480,000 



1,060,000 



7,500,000 



16,100,000 



31,400,000 



46,000,000 



1.98 



+L 

 + L 



+M 



+ L 



- 



2.06 

 2.08 

 2.09 

 2.14 



1.94 



2.08 

 2.08 

 2.30 

 2.47 



1 See footnote under Table 1. 



EFFECT OF PHOSPHATES. 



We have so far discussed in a general way the effect of increasing 

 the acidity of milk by the addition of lactic acid and by the generation 

 of the acid in milk. Since the acidity of milk when titrated with 

 phenolphthalein is due partly to acid phosphates, it will be of interest 

 to show the effect on the alcohol test of the increase in acidity by 

 acid phosphates. In Table 5 are shown the results of a few tests, 

 using sodium and potassium acid phosphate. Various amounts of 

 a 5 per cent solution of these salts were added to 50 c. c. of milk. It 

 will be seen from the table that when the acidity was increased by 

 sodium acid phosphate from 2.15 to 3.33 the alcohol test with 75 



