MBRT Test Calculator — Milk Bacteriological Quality Grade

What is the MBRT Test?

The Methylene Blue Reduction Time (MBRT) test is a rapid, indirect method to assess the bacteriological quality of raw milk. It works because bacteria in milk consume dissolved oxygen and reduce the methylene blue dye, causing the blue colour to disappear.

The faster the dye decolourises, the higher the bacterial load — and the poorer the milk quality.

How to Use This Calculator

1. Enter the time taken (in hours and minutes) for complete decolourisation of the methylene blue dye
2. The calculator assigns the IS 1479 quality grade and recommends accept/reject action

MBRT Quality Grades (IS 1479 Part I)

Test Procedure

1. Add 1 mL of methylene blue solution (0.005%) to a sterile test tube
2. Add 10 mL of well-mixed milk sample
3. Stopper the tube and mix by inversion (2–3 times)
4. Place in water bath at 37°C ± 0.5°C
5. Start the timer
6. Check every 30 minutes (check at 30 min, 60 min, 2 hr, 5 hr)
7. Record time when the blue colour completely disappears

Factors That Affect MBRT

• Milk temperature during collection: Warm milk bacteria multiply rapidly
• Transport time: Unrefrigerated transport increases bacterial count
• Udder health: Mastitic milk has higher bacterial count
• Container hygiene: Contaminated containers reduce MBRT
• Seasonal variation: Hot summer months often show shorter MBRT

Minimum MBRT Requirements by Application

Important Notes

• MBRT is an indirect test — always confirm Grade 4 milk with direct colony count
• MBRT gives cumulative bacterial count, not identification of type
• Colostrum gives a false short MBRT due to antibody content — test separately
• Very fresh, high-SCC mastitic milk may also give abnormal results