Three Tankers, Three Different Problems: Classifying Adulterated Milk
A district milk union collects 40,000 litres a day from 22 village societies and supplies a government school milk scheme. During a surprise check the food safety officer draws samples from three tankers. Tanker A: fat 3.1%, SNF 7.4%, freezing point −0.410°C, no starch and no urea on screening. Tanker B: fat 4.4%, SNF 8.5%, freezing point −0.545°C, but the sample lathers persistently on shaking, has a faint soapy smell, and shows a methylene blue reduction time of 6.5 hours. Tanker C: fat 4.6%, SNF 8.7%, freezing point −0.548°C, urease test positive and urea estimated at 1,450 mg/litre. All three tankers are declared as mixed cow and buffalo milk. The union's chilling centre records 6°C at 05:00 and 11°C at 09:00; the tankers reach the school kitchen at 13:30. The officer must separate substandard from unsafe, and must document the added water arithmetically.
1. Quantify the added water in Tanker A and explain why fat and SNF alone would have been a weak case.
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Calculation. Authentic mixed milk freezes at about −0.540°C. Added water pushes the freezing point towards zero in proportion to the dilution:
Added water (%) = (FPD of authentic milk − FPD of sample) / FPD of authentic milk × 100 = (0.540 − 0.410) / 0.540 × 100 ≈ 24%.
A 24% dilution is consistent with the depressed fat (3.1% against the declared mixed-milk standard) and SNF (7.4%).
Why fat and SNF are not enough. A dishonest supplier can add water and then restore the solids with skim-milk powder or whey, so that fat and SNF read normal while the milk is still diluted. The freezing point is a colligative property: it responds to the total dissolved solute load and cannot be restored by the same trick, because diluting water raises the freezing point, and the arithmetic then exposes the added volume. This is why cryoscopy, not the lactometer alone, is decisive.
Classification. This is sub-standard food (not of the nature, substance or quality demanded) rather than unsafe food, unless the added water was itself contaminated. The correct charge is the sub-standard provision, supported by fat, SNF, cryoscope reading and the calculated dilution figure recorded in the sampling memo.
2. What is your finding on Tanker B, and how does the MBRT result change the action?
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Finding: detergent contamination. Persistent lather on shaking, a soapy smell and normal fat, SNF and freezing point together point to a surface-active agent, typically a detergent used to wash cans or vessels and then inadequately rinsed. The freezing point is unaffected because the contaminant is not a simple solute added to dilute the milk.
Legal character. A detergent is not a permitted ingredient and is not a normal constituent of milk; it can cause gastrointestinal injury. This is unsafe food rather than merely sub-standard, and the adulterant provisions also apply. The case is a prosecution-grade matter, not a compounding matter.
Confirmatory work. The field foam test is only indicative: the notified laboratory should run the methylene blue–chloroform extraction for anionic detergents, and the sample must reach the laboratory without delay and with cold storage documented.
Role of the MBRT. A reduction time of 6.5 hours indicates only fair bacteriological quality; it does not prove the milk unsafe and must not be used to inflate the charge. It is evidence of a cold-chain or hygiene weakness at the society, which justifies a separate improvement notice on the chilling centre - note that the 11:00 reading and the 13:30 delivery are outside good practice. Keep the detergent charge and the hygiene charge separate, or the strong case will be weakened by the weak one.
3. How should Tanker C be handled, and what does the natural urea background mean for the case?
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Finding: added urea. Urea at 1,450 mg/litre is far above the natural background of roughly 200–700 mg/litre in milk, and the urease screen is positive. Urea is added to raise the apparent SNF and to mask dilution, and it is not a permitted additive.
Why the background matters. Because urea occurs naturally, a single borderline value cannot sustain a prosecution. The case must rest on: (i) a value well outside the physiological range, (ii) the DMAB colorimetric confirmation or an equivalent instrumental method at the notified laboratory, and (iii) corroboration - freezing point, SNF and the society's purchase records for fertiliser-grade urea, if any. State all three in the memo.
Legal character. Urea is an adulterant; where the quantity is capable of causing injury it is also unsafe food. The charge should reflect the actual risk, not be inflated automatically.
Action. Stop despatch from that society's route, withhold the tanker's milk from the school scheme, draw a second sample from the society's bulk cooler for the chain of evidence, and record that the tanker was at 11°C on arrival - an independent food-safety failure on the same consignment. Serve the society with a notice and pursue the supplier who introduced the urea, since the union's own records will usually identify the collection point.