114 EXPEKIMENT STATION EECOED. 



added to the milk with dibasic phosphate, the alcohol test became positive; 

 that is, when the dibasic phosphate had been converted into monobasic phos- 

 phate, then further increases in acidity caused a positive alcohol test. As a 

 very general explanation of this result, it may be said that when acid is added 

 to milk it converts the dibasic phosphate into the monobasic phosphate. It 

 follows that the acid, and also the monobasic phosphate, probably affect the 

 casein and thereby change it into a condition in which it Is possible to pre- 

 cipitate the casein by alcohol and cause a positive test. This action on the 

 dibasic phosphate probably explains in part the positive alcohol tests with 

 different low acidities." 



The addition of 1 per cent of sour milk to fresh milk caused a positive 

 alcohol test with 75 per cent alcohol and the addition of 2.5 per cent of sour 

 milk caused a reaction with 68 per cent alcohol. As much as 10 per cent of 

 sour milk was necessary to cause coagulation with 44 per cent alcohol. Milk 

 in which the acidity was increased to 4.3 per cent by the addition of lactic acid 

 and then reduced to 1.9 per cent by neutralization gave a positive alcohol test 

 with 68 per cent alcohol. " The positive alcohol tests with 68 per cent alcohol 

 could be made negative at acidities below 4..S by reducing to about the original 

 acidity of the normal milk." 



Some milks when heated to 90° C. wiU not give the alcohol test with 75 or 

 08 per cent alcohol. 



To determine the effects of rennet on the outcome of the alcohol test (75, OS, 

 and 44 per cent) rennet in percentages ranging from 0.00005 to 0.0015 was tried 

 and the tests v/ith alcohol were made at intervals of one hour. " The results 

 show that the action of rennet in milk may produce changes which cause a 

 positiA'e alcohol test and that two main factors are of importance, viz, the 

 amount of rennet and the length of time the rennet has to act. Undoubtedly a 

 third factor must be taken into consideration ; that is, the temperature at which 

 the milk is held. In the experiments the milk was held at room temperature." 

 The activity of rennet-forming bacteria may cause a positive alcohol reaction 

 but the number of bacteria propagated must be large. A test Indicated that it 

 is also possible to differentiate between an acid and rennet fermentation in 

 milk on the basis of the alcohol test. When sufficient rennet was added to milk 

 to cause a positive alcohol reaction and then heated to 90° C. the milk no longer 

 gave a positive alcohol test with 75 per cent alcohol, although rennet and acid 

 probably play the principal role in obtaining a positive alcohol test. 



The presence of carbon dioxid may also be considered a factor. Carbon 

 dioxid passed into milk will cause an alcohol test. Alkali-forming bacteria 

 will not cause a positive alcohol test. With samples of market milk no rela- 

 tion was found between the bacterial count and the alcohol test. In this work 

 particular attention is drawn ''to the bacterial counts of 142 samples of raw 

 milk which ranged from 2,000 to 19,600,000 bacteria x^er cubic centimeter. Of 

 these 142 samples none gave a ix)sitive alcohol test, yet 86, or 60.6 per cent, 

 contained less than and 39.4 per cent more than 500,000 bacteria per cubic centi- 

 meter. The bacterial counts of samples of pasteurized milk which gave a nega- 

 tive alcohol test ranged from 1,200 to 3,600,000 per cubic centimeter. . . . 

 When the 08 per cent alcohol test is positive with a sample of market milk, it 

 is evident that there is some change in the milk from normal. In some cases it 

 may be due to an increased acidity and in consequence a change in the casein 

 of the milk, due to bacterial action. In other cases it may be due to a pure 

 rennet fermentation or there may be a combination of an acid-and-rennet fer- 

 mentation. In such ca.ses the bacterial count would undoubtedly be high. How- 

 ever, there still remains to be explained the reason for a positive alcohol test 

 in samples of market milk with a low bacterial count and low acidity." 



