A Low-SNF Delivery at the Village Collection Centre
At a village milk collection centre in Khordha district, the morning pool of 420 L tests 4.5% fat and 8.6% SNF. One supplier, who delivers 80 L in two cans, shows 3.0% fat, 7.5% SNF, a lactometer reading of 25 at 29°C, and a faint watery appearance; the sediment test is negative. The centre's Gerber test gives duplicate fat values of 2.9% and 3.1%. The supplier claims his cows are in late lactation and that low SNF is normal for his herd. The centre has a lactometer, butyrometer, Gerber centrifuge, thermometer, and a freezing-point cryoscope that is calibrated monthly. The milk is still in the supplier's cans and has not been mixed with the pool. The society's rule is that payment is based on fat and SNF, with a penalty for adulteration, but the secretary does not want to punish a member on one doubtful sample.
1. Which confirmatory tests should be run on the 80 L before rejecting it, and how would you interpret them together?
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Start with the freezing-point test because it is the most direct evidence of added water. Normal cow milk freezes between about −0.530°C and −0.550°C; added water moves the value toward 0°C while genuine late-lactation milk normally keeps a normal freezing point. Support this with chloride, ash, lactose and the SNF:fat ratio. In late lactation, fat and SNF usually rise together, not fall together. Here fat has fallen to 3.0% and SNF to 7.5% at the same time, which is the pattern of dilution rather than a herd effect. The lactometer reading must be temperature-corrected before use; a raw reading of 25 at 29°C cannot be compared directly with a reading taken at 27°C. Do not rely on starch or sugar tests as the primary evidence, because they detect other adulterants, not water. If the supplier disputes the result, seal a duplicate sample with preservative, label it with time, temperature and sample identity, and send it to the district laboratory.
2. If the cryoscope reads −0.48°C, estimate the extent of added water and check whether the fat and SNF figures are consistent with that estimate.
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Use the freezing-point depression as a dilution guide: percentage added water ≈ [(normal freezing point − observed freezing point) ÷ normal freezing point] × 100. Taking the normal value as −0.54°C gives (0.54 − 0.48) ÷ 0.54 × 100 ≈ 11.1%. Cross-check with solids: if the original fat was 3.0 ÷ (1 − 0.111) ≈ 3.37% and the original SNF was 7.5 ÷ 0.889 ≈ 8.44%, both values are plausible for cow milk. A second estimate from SNF, assuming a normal 8.5%, gives (8.5 − 7.5) ÷ 8.5 × 100 ≈ 11.8%. The two estimates agree within about one percentage point, which strengthens the conclusion that roughly 11% water was added. If the freezing point had been normal while fat and SNF were low, the explanation would more likely be a genuine herd or feeding effect, and rejection would be unsafe. Record the cryoscope calibration check with the result.
3. What action is fair and legally defensible for the society to take against this supplier?
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Segregate and reject the 80 L; do not mix it with the 420 L pool and do not pay for it as milk. Record the sample identity, time, temperature, duplicate fat results, cryoscope reading and the witness present. Issue a written notice under the society's bylaw, not by the secretary's informal decision. Offer a repeat sample at the next delivery and arrange random sampling of that supplier for at least two weeks. If the supplier disputes the finding, preserve a duplicate and abide by the district laboratory result. At the same time, check whether other suppliers show the same freezing-point shift; if several do, investigate the centre's water supply, can-washing practice or sampling technique before blaming individuals. Counsel the member privately on clean milk production. The penalty should be proportionate, documented and applied consistently, because an unfair accusation can damage member confidence while an unrecorded warning leaves the society unable to defend its quality rule.