24 



BULLETIN 202, U. S. DEPARTMENT OP AGRICULTURE. 



Table 19. — Acidity and bacterial count of samples of pasteurized market milk which 

 gave negative alcohol tests with 75 per cent, 68 per cent, and 44 per cent alcohol. 



Sam- 

 ple 

 No. 



Acid- 

 ity. 



Bacteria 



per cubic 



centimeter. 



Sam- 

 ple 

 No. 



Acid- 

 ity. 



Bacteria 



per cubic 



centimeter. 



Sam- 

 ple 

 No. 



Acid- 

 ity. 



Bacteria 



per cubic 



centimeter. 



1 



1.85 



1,200 



20 



1.75 



15,000 



39 



1.85 



104,000 



2 



1.77 



1,200 



21 



1.70 



16,000 



40 



2.05 



110,000 



3 



1.66 



1,900 



22 



1.65 



16,000 



41 



1.65 



114,000 



4 



1.75 



3,000 



23 



2.05 



16,000 



42 



1.76 



120,000 



5 



1.66 



4,000 



24 



1.69 



17,500 



43 



1.80 



133,000 



6 



1.80 



5,000 



25 



1.78 



21,000 



44 



1.75 



194, 000 



7 



1.85 



7,000 



26 



1.66 



21,000 



46 



1.73 



264,000 



8 



1.85 



7,600 



27 



1.80 



24,000 



47 



1.70 



284,000 



9 



1.80 



8,000 



28 



1.83 



32,000 



48 



1.90 



340,000 



10 



1.80 



9,000 



29 



1.67 



37,000 



49 



1.76 



446,000 



11 



1.71 



9,000 



30 



1.96 



41,000 



50 



1.85 



720,000 



12 



1.75 



11,000 



31 



1.75 



52,000 



51 



1.65 



740,000 



13 



1.85 



11,000 



32 



1.90 



59,000 



52 



1.75 



940,000 



14 



1.70 



11,000 



33 



1.85 



62, 000 



53 



1.74 



1,280,000 



15 



1.65 



12,000 



34 



1.85 



64, 000 



54 



1.60 



1,660,000 



16 



1.85 



13,000 



35 



1.70 



65,000 



55 



1.97 



2,460,000 



17 



1.75 



14,000 



36 



1.75 



68,000 



56 



1.60 



3,100,000 



18 



1.75 



15,000 



37 



1.80 



71,000 



57 



2.00 



3,600,000 



19 



1.80 



15,000 



38 



1.70 



74,000 









In the early stages of the growth of acid-forming bacteria in milk , 

 when the numbers are low, there is a period in which a rapid increase 

 in numbers takes place without any increase in acidity which can be 

 detected by ordinary chemical methods, or it may occur with only a 

 slight increase in acidity; consequently if the alcohol test were made 

 during that period there would be a high bacterial count and yet not 

 high acidity enough to cause a positive alcohol test. The same is 

 true of the action of the rennet-forming bacteria in their growth and 

 action, as we have shown earlier in this paper when dealing with the 

 relation of acidity, and also the effect of rennet on the alcohol test. 

 Besides these facts there are other groups of bacteria which may 

 develop in milk and yet have no influence on the alcohol test, as, for 

 example, the alkali-forming group of bacteria. We have tried cul- 

 tures of this group of organisms and found that they did not produce 

 a positive alcohol test. There are other groups of bacteria in the 

 flora of milk, such as the inert group, which also would probably 

 develop without influencing the alcohol test in any way. When we 

 consider all these facts it is not strange that there is no definite 

 relation between the bacterial flora of milk and the bacterial count. 



When the 68 per cent alcohol test is positive with a sample of 

 market milk, it is evidence 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 fermentation. 

 In such cases 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. 



