Cooling logs at a cook-chill central kitchen
At 22:30 a cook-chill central kitchen in Kwai Chung finishes 200 kg of steamed rice and 120 kg of braised chicken for 180 meals going to three residential care homes. One blast chiller is out of service. The night supervisor loads the food into 20 cm deep stainless pans and puts them in the walk-in cooler, noting that the pans are 'still cold to the touch'. The cooling log records 20°C at 4 hours and 8°C at 7 hours. Next morning the kitchen reheats the chicken to 65°C for 10 minutes and holds it at 62°C for service. The rice is left in the preparation room for 3 hours before reheating. Two days later, 14 residents develop watery diarrhoea, 11 within 8–14 hours; three also vomit. No fever. The manager asks whether the batch can be served and whether the reheating step made it safe.
1. Identify the time-temperature control failures and explain which microorganisms are most plausibly involved.
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The critical control is rapid cooling through the danger zone (4–60°C). The batch was 20°C at 4 hours and 8°C at 7 hours, so it spent far too long in the danger zone; 20 cm deep pans and a failed blast chiller explain the slow rate. Rice held at room temperature for 3 hours adds a second abuse. The likely agents are Bacillus cereus from rice and Clostridium perfringens from slowly cooled chicken. The clinical picture - watery diarrhoea with an 8–14 hour onset - fits C. perfringens, but the rice cannot be excluded. Reheating to 65°C for 10 minutes is not a corrective control: it may kill vegetative cells but does not destroy heat-stable toxins or spores, and 65°C is below a robust reheating target such as 75°C. The food was not made safe by reheating.
2. What should be done with the remaining food and with the meals already delivered?
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Hold all remaining packs at 4°C or below in a segregated area, label them 'do not use', and sample before disposal. Do not serve or reheat. Notify the three care homes immediately to stop service and hold leftovers, advise them to seek medical advice for symptomatic residents, and report the incident to the Centre for Health Protection and FEHD. Retrieve delivered packs where possible; if already eaten, record exposure. Collect food, environmental swabs and stool samples, and keep the cooling log. Discard the batch after sampling because it is implicated and the time-temperature abuse cannot be reversed. A recall may be needed if other homes received the same batch. Record all decisions and notify the licensee's senior management.
3. Propose corrective actions and monitoring that would prevent recurrence, including what to do when a blast chiller fails.
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Repair and validate the blast chiller; do not run cook-chill without a validated cooling method. Reduce pan depth (for example to 5 cm or less), use the blast chiller or an ice bath with stirring, and record core temperature at start, 2 hours and end. Set a validated target such as 60→20°C within 2 hours and 20→4°C within a further 2 hours. If the target is not met, treat it as a deviation: if food has been more than 4 hours in the danger zone, discard; do not recool and sell. Add a pre-shift chiller check, alarm and data logger, and a written contingency plan for chiller failure. Verify through weekly log review and trend analysis, and train night staff. Because rice is high-risk, cool it in thin layers and never hold it at room temperature.