LABORATORY MANUAL 
08 
EXERCISE NO. 52 
Object: To become acquainted with the Methylene blue reduction test and the 
Fermentation test of milk. 
Procedure: The fermentation test and the Methylene blue test may be 
performed separately as an individual test or they may be com¬ 
bined as one test. The tests are of greatest value to the cheese 
maker to detect abnormal fermentations. They may be used 
^ by the buttermaker as well to locate off-flavors. They are of 
greatest value when combined with the acidity test for then 
they will give a clue to the kind of organisms present. The 
aim of the Methylene blue test is to place the milk into certain 
defined grades which may be tabulated somewhat as below. 
The number of organisms, of course, is relative and is given 
merely as a matter of interest. 
Grade 
White after 
Organisms 
1 
53^ hrs. 
0-500,000 
2 
2-5 V 2 hrs. 
500,000-4,000,000 
3 
H-2 hrs. 
4,000,000-20,000,000 
4 
Less than 3^ hr. 
20,000,000-up ward 
A. Wash and clean five test tubes. Sterilize by placing in a w're 
basket and placing under a pail which has been inverted over 
a steam jet. The steam is then turned on for a period of 15 
minutes. If no steam is available the test tubes may be placed 
in boiling water for 10 minutes. 
B. Use one test tube for each patron. Catch the milk in the test 
tube directly out of the patron’s can while the can is being 
dumped. Add 1 cc. of Methylene blue solution to each test 
tube and mix. Place the test tube in an incubator at 98° F. 
Observe after hourly intervals and record the color ot the milk. 
Compare with the table above. 
C. If the test tubes are left in the incubator for 24 hours and their 
ap pearance noted it will be possible to determine to what class 
of organism the reduction was due. The appearance of the 
milk in the test tubes is also indicative of the quality of cheese 
which it will make. The fermentation test may be made inde¬ 
pendent of the Methylene blue test. 
