In the methylene blue reduction
(MRBT) test 1 ml of methylene blue (1: 25,000) is added to 10 ml of milk. The
tube is sealed with rubber stopper and slowly inverted three times to mix. It
is placed in a water bath at 35°C and examined at intervals up to 6 h. The time
it takes for the methylene blue to become colourless is the methylene blue
reduction time (MBRT). The shorter the MBRT, the lower the quality of milk.
Table: Grading of milk samples on
the basis of methylene-blue reduction test in different milk samples.
Quality of milk
Decolourization time
Excellent More than 5 h
Good Between 4 hours and 5 h
Fair Between 3 to 4 h
Poor Less than 2 h
