Sour, rubbery paneer and two customer complaints in Alwar
A halwai-cum-dairy in Alwar collects 500 L of cow milk each morning from 12 farmers, transports it in open cans on a motorcycle trolley, and chills it only after reaching the shop at 11 a.m. In July, evening milk is held overnight in a stainless steel vat with a loose lid and no agitator. Morning paneer made from it gives 11.5 kg per 100 L, against the unit's normal 14 kg. The cubes are rubbery and slightly sour and the whey is cloudy. A sample shows fat 3.8%, SNF 8.2% and titratable acidity 0.21% lactic acid, against 0.14–0.16% for fresh mixed milk. The MBRT on the vat sample reads 45 minutes, where the laboratory's reference for good milk is 4 hours or more. Two customers have complained of loose motions after eating the paneer. The halwai blames the citric acid he uses for coagulation and wants to switch to lemon juice and increase the acid dose to get a firmer cake.
1. Interpret the analytical results. What do the acidity, MBRT, SNF and yield figures tell you, and how likely is the coagulation acid to be the real cause?
Read the worked answer
The raw milk is the problem, not the coagulant.
Reading the numbers:
- Acidity 0.21% lactic acid against 0.14–0.16% fresh means roughly 0.05–0.07 percentage points of acid have been produced by bacterial growth. Milk typically begins to clot and behaves badly by about 0.20–0.22%, so this vat is already at the edge of spontaneous souring.
- MBRT 45 minutes is a poor-quality result (a reduction time under about 2 hours indicates a high initial bacterial load; 4 hours or more is good). This is a direct measure of how many bacteria were in the milk, consistent with the acidity and with eight or more hours of unagitated, uncovered holding in July.
- SNF 8.2% is below the legal minimum of 8.5% for cow milk, which points to added water or to milk from poorly fed animals - a compliance issue in its own right and part of why yield is low.
- Yield 11.5 kg/100 L against 14 kg and cloudy whey: cloudy whey means casein fines lost because the curd shattered. Pre-acidified milk coagulates fast and unevenly, the curd is weak, and much of the protein never makes it into the block. Rubbery texture fits over-acid curd pressed hard.
Verdict on the citric acid: very unlikely to be the cause. Switching to lemon juice changes nothing chemically - both are acids - and increasing the dose on already-sour milk will make the curd shatter more and the paneer sourer. The fault runs upstream: time-and-temperature abuse of raw milk.
2. Set out the process changes needed - collection, chilling, heat treatment, coagulation, pressing, chilling - and explain whether the 14 kg yield is recoverable.
Read the worked answer
Collection and chilling (the 80% fix)
- Chill milk to 4 °C within 2–3 hours of milking: insulated cans, ice packs or a bulk cooler at the collection point. Do not carry 8 hours of warm milk on a trolley and then chill it.
- Test each farmer's milk at receipt - acidity, MBRT or a rapid platform test - and pay on quality; reject milk above 0.16% acidity or with a poor MBRT.
- Evening milk must be chilled overnight with the vat covered, and ideally not held beyond 12–24 hours.
Heat treatment
- Pasteurise: 63 °C for 30 minutes or 72 °C for 15 seconds, then cool to coagulation temperature. This kills the vegetative pathogens behind the loose-motions complaints and gives a repeatable curd.
Coagulation and pressing
- Heat to 70–75 °C, add about 0.1% citric acid as a dilute 1–2% solution slowly with gentle agitation, and stop at pH 5.2–5.3 - not at a fixed volume of acid.
- Hold 10 minutes for the curd to firm, then drain; do not stir a set curd. Press progressively, then chill the block in potable chilled water.
Is 14 kg recoverable? Largely yes, but not entirely with 3.8% fat and 8.2% SNF. Yield is a function of casein and fat: recovering the fines lost to cloudy whey should bring the figure back close to normal, and correcting the SNF shortfall (water adulteration, feeding) is what recovers the rest. Expect your normal figure only when the milk meets the legal SNF minimum.
3. Two customers report loose motions. What should the unit do now, and which records and regulatory steps matter?
Read the worked answer
Stop selling the product and treat this as a suspected food-borne illness, not a customer complaint.
Immediate actions
- Withhold and destroy all paneer from that vat and any stock made from the same milk; do not try to sell it quickly or convert it into another product.
- Contact the two customers, ask them to see a doctor, and record what and when they ate and what symptoms they had. Take complaints seriously and in writing.
- Report to the district Designated Officer / FSSAI and cooperate with any sampling. Where a food-borne illness is suspected, an early, honest report is far less damaging than a late one.
- Sample and test the retained milk, the paneer, the water used for chilling and washing, and the handlers' hands for coliforms, Staphylococcus aureus and Salmonella. Poor hygiene and infected skin lesions are common sources in a halwai kitchen.
- Sanitise vats, cans, cloths and presses; a loose-lidded vat and open transport cans are also a cleaning problem.
Records that matter
- Milk receipt register: farmer, litres, time, temperature, acidity/MBRT.
- Batch card linking milk received to paneer made, quantity and dispatch.
- Pasteurisation temperature/time log, water test reports, cleaning log, staff health and training records.
- These records are both the legal defence and the only way to trace a bad batch back to its source.
Do not resume until the raw-milk chilling chain is fixed and at least two consecutive batches pass microbiological screening.