Cooperative Pooled Milk Failing the MBR Test and Adulteration Screen
A village dairy cooperative in Kolhapur collects about 1,800 L of pooled buffalo milk twice a day in aluminium cans from 120 member farmers. Payment is on fat and SNF, and the tanker leaves at 8 a.m. During one week the methylene blue reduction (MBR) test on the pooled evening milk decolourised in 45 minutes, and the chilling centre rejected two tanker loads. Three individual member samples tested that week gave: fat 6.2% and SNF 8.4% (the society's normal for buffalo milk is 6.5% and 9.0%), lactometer reading 26.0 at 30 °C, freezing point −0.478 °C, and one sample gave a faint blue-black colour with iodine solution. The society's tap, used both for drinking and for washing cans, is unchlorinated. Cans are rinsed once, inverted to dry on the grass outside, and evening milk stands in the collection room until the 6 a.m. can is filled. Three members are known to keep their milk overnight in brass vessels.
1. Interpret each test result and state what it does and does not prove.
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MBR decolourisation in 45 minutes. Methylene blue is reduced when bacteria (and to a lesser extent somatic cells) consume oxygen. A reduction time under 2 hours is graded very poor; over 8 hours is good. 45 minutes proves a very heavy bacterial load or a large admixture of mastitis milk. It does not by itself identify which farmer caused it, and it does not distinguish mastitis from dirty utensils.
Fat 6.2% and SNF 8.4%. Both below the society's buffalo norm. Either the milk is diluted, or it comes from late lactation/early lactation animals, or from a herd with poor feeding. On its own this is only a flag.
Lactometer 26.0 at 30 °C. Low for buffalo milk; correcting to the standard 27.5 °C would give a still lower value. Supports dilution but is not conclusive, because the lactometer reading also depends on temperature and on the fat left in the sample.
Freezing point −0.478 °C against a normal −0.52 to −0.55 °C. This is the decisive test for added water. Each 1% of added water raises the freezing point by about 0.0055 °C, so the shift here corresponds to roughly 7–8% added water. It cannot be explained by feeding or stage of lactation.
Iodine blue-black colour. Starch or flour has been added. This cannot occur from the animal; it is deliberate adulteration.
Summary: two separate problems - deliberate adulteration (water plus starch) by at least one supplier, and a general hygiene failure across the pool.
2. How should the society deal with the three members, and why is communication as important as punishment here?
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Technical handling
- Stop pooling the three samples; test each can separately at the dock in front of the member, in duplicate, and record the result in the register with the member's signature.
- Apply the by-laws: warning on the first proven offence, price penalty on the second, suspension of supply on the third. The freezing point and iodine results are defensible evidence; the fat/SNF figures alone are not.
- Run a CMT (California Mastitis Test) on each quarter of the suspect animals - mastitis milk raises cell count, reduces MBR time and is a legitimate, non-culpable cause of poor quality.
- Resample these members' milk every delivery for the next three deliveries before restoring normal status.
Why communication matters A punitive-only response drives members to the private milk trader, who pays cash and tests nothing; the society then loses volume and cannot meet the tanker's commitment. Extension works better: hold a demonstration at the society in which members themselves perform the iodine test, the lactometer reading and the freezing point test on their own samples and see the result. Explain that water costs them money twice - it is bought at the price of milk and it gets the whole pool rejected. Explain that brass vessels speed up oxidative rancidity through copper and that an unclean can destroys the value of a whole morning's milk. Pair the warnings with a practical route to compliance: a proper can-washing point, brushes, chlorine, and a drying rack.
3. Design a quality-control plan for the collection centre, addressing utensils, water, cooling and pricing.
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At the dock
- Sample every can, weigh it, and test fat, SNF, MBR and a rapid adulteration screen before acceptance; reject on the spot, not after pooling.
- Keep a sample drawer or retention samples for 24 hours for disputes.
Utensils
- Three-step wash: cold rinse, hot detergent wash at 60–70 °C with a brush, then sanitising rinse (chlorine 100–200 ppm) - never a single rinse.
- Dry cans inverted on a slatted rack in the sun, never on grass.
- Encourage stainless steel or food-grade plastic; brass and unlined iron cause rancidity and off-flavour.
Water
- The wash water must be potable; chlorinate the society's tank and test it monthly. Unchlorinated water used for rinsing recontaminates clean cans and is also a source of added-water disputes.
Cooling and holding
- Evening milk should reach 4–5 °C within about two hours; if the society has no bulk milk cooler, arrange a chilling tank or shift evening collection to an early-night pick-up. Holding at ambient overnight is the single largest contributor to the 45-minute MBR.
- Cold chain records (time and temperature log) should travel with every tanker load.
Pricing and training
- Introduce a quality-linked premium and penalty so that clean milk pays, not only high fat.
- Train members on udder washing, discarding foremilk, dry-hand milking, teat dipping and dry cow therapy, since mastitis milk is a hidden cause of poor MBR results.