Forty-Five Litres Overnight: Cooling, Reheating and Hot Holding
A 120-cover restaurant cooks 45 litres of chicken curry and 30 kg of yellow rice at 19:00 each evening for the next day's lunch service. The lidded pots are left on the switched-off range until 07:00, then moved into a 4 °C walk-in chiller that is already about three-quarters full. At 08:00 a probe inserted into the centre of the curry reads 18 °C. At 10:30 the curry is reheated in the same pots until it 'bubbles at the edges', then transferred to a bain-marie holding 55–60 °C until service ends at 14:30. On Tuesday, six customers and two staff who ate the curry at 12:30 developed abdominal cramps and watery diarrhoea between 22:30 and 00:30; none vomited and all recovered within 24 hours. Rice from the same meal was not implicated. The chef blames the customers, saying 'Sri Lankan stomachs are weak'.
1. Which organism best fits this pattern, and what in the operation explains it?
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Best fit: Clostridium perfringens.
- Timing: illness at 22:30–00:30 after a 12:30 meal is a 10–12 hour incubation - the classic window for C. perfringens (typically 8–12 hours).
- Symptoms: watery diarrhoea and cramps, no vomiting, recovery in about 24 hours. Compare S. aureus or B. cereus emetic toxin, which give vomiting within 1–6 hours; those are excluded by the onset time and symptom pattern.
- Vehicle: a large volume of meat-based stew. Spores survive cooking, and the slow cooling of a 45-litre pot keeps the centre in the danger zone (5–60 °C) long enough for spores to germinate and cells to multiply to a high dose.
- The 08:00 reading of 18 °C is the smoking gun. Eleven hours after cooking, the centre of the curry was still well above 5 °C. The pot went from ambient overnight holding into a chiller that was three-quarters full, so it cooled even more slowly once inside.
Reheating to 'bubbling at the edges' may kill vegetative cells, but a large dose of cells and spores has already been built up, and C. perfringens produces its toxin in the intestine during sporulation after ingestion. The chef's remark about 'weak stomachs' is both wrong and beside the point: the fault is a cooling failure, not the customers.
2. Write the cooling procedure you would require for the curry, with figures, and explain the practical obstacles in this kitchen.
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Required cooling procedure (two-stage)
- Cool from 60 °C to 21 °C within 2 hours, then from 21 °C to 5 °C within a further 4 hours - a maximum of 6 hours in total.
- Achieve this by decanting into shallow pans no more than 5 cm deep (or several smaller pots), leaving lids off in a clean, protected area while steaming stops, and using an ice bath, stirring, or a blast chiller where available.
- Probe and record: temperature of the centre of each container at the start, at the 2-hour mark, and at the end, with the time and initials written on a cooling log.
- Date-label and place in the chiller so that cold air can circulate around each container; nothing goes in above another open container of ready-to-eat food.
Obstacles here
- Thermal mass. 45 litres in one lidded pot cannot cool to 5 °C in a fridge overnight, let alone in 6 hours. Splitting the batch is the whole solution - the pot is the problem.
- A three-quarters-full chiller. The unit is at 4 °C air temperature, but adding a hot pot raises the whole cabinet's temperature and jeopardises everything else stored in it. Air temperature is not food temperature; only a probe tells you the truth.
- No cooling log exists, so the failure was invisible until people became ill.
If the kitchen cannot meet the schedule with the equipment it has, the honest alternative is to cook the curry fresh each morning or reduce the batch size, not to leave 45 litres on a stove overnight.
3. The bain-marie holds 55–60 °C. Evaluate the reheating and hot-holding steps and state what you would change.
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Reheating 'Bubbling at the edges' is not a measurement. Reheating must bring all of the food, including the centre, to at least 75 °C, and it must be done within 2 hours, once only. A 45-litre pot on a range can easily have 75 °C at the sides and 50 °C in the middle, which is exactly what 'bubbling at the edges' describes. Probe the centre of the thickest part of each pot, record the reading, and stir before probing to avoid a false hot spot. Reheat in small batches, not in the bulk pot.
Hot holding 55–60 °C is below the safe hot-holding threshold. Food should be held at 60 °C or above, with 63 °C the usual operating target so that there is a margin for error. The bain-marie is also a holding device, not a cooking device: it cannot safely bring cold curry up to temperature, which is why the curry must be fully reheated in a pot first and then transferred.
What to change
- Reheat to 75 °C or above within 2 hours, probed and recorded; never reheat the same batch twice - leftovers at the end of service are discarded.
- Hold at 63 °C or above, and check and record the temperature every 2 hours during service.
- Any food found below 60 °C is discarded if the time out of temperature is unknown or exceeds 2 hours; do not simply turn the bain-marie up and carry on.
- Service staff should be able to say who checks the bain-marie and where the record is kept; a log nobody fills in is worse than none, because it creates false confidence.
Together with the cooling fix, these three disciplines - cool fast, reheat hot, hold hot - address the whole chain that produced Tuesday's illnesses.