The Chiller That Crept Up Overnight
A Dubai catering kitchen stores raw chicken, cooked rice, sliced tomatoes and a cream cake in a single walk-in chiller. On Monday at 18:00 the chiller reads 3°C. On Tuesday at 06:00 the display reads 9°C; the door seal is torn and the kitchen had a 2-hour delivery window with the door propped open from 02:00 to 04:00. The internal probe of the chicken reads 8°C; the rice reads 9°C; the cake reads 7°C. The manager wants to 'blast chill it back down and use it for lunch'. The kitchen has a 4-hour rule for food held above 5°C. No temperature log exists for the overnight period.
1. For each of the four foods, decide whether it can be kept, and justify using the temperature danger zone and the 4-hour rule.
Read the worked answer
Raw chicken (8°C): Raw poultry is a high-risk food. It has been above 5°C for an unknown period (up to 8 hours if it rose gradually). It cannot be verified as safe. Discard - the risk of Salmonella and Campylobacter growth is too high, and there is no kill step recorded before service.
Cooked rice (9°C): Cooked rice is a classic B. cereus vehicle. Held at 9°C for an unknown period, it exceeds the 4-hour rule. Discard.
Sliced tomatoes (7°C): Cut tomatoes are a high-risk RTE food because of their moisture and pH. Above 5°C for an unknown period. Discard unless a verified time record shows under 4 hours - which it does not.
Cream cake (7°C): Cream is a high-risk RTE food (dairy, Listeria risk). Discard.
Key reasoning: The 4-hour rule is a cumulative limit across the food's life above 5°C, not a per-event allowance. Without a log, you cannot demonstrate the food stayed under 4 hours, so the precautionary principle applies: discard. 'Blast chilling back down' does not undo bacterial growth or toxin already formed.
2. The manager proposes blast-chilling the food back to 5°C. Explain why this does not make the food safe.
Read the worked answer
Blast chilling stops further growth but does not reverse what has already happened. Two problems:
- Bacterial numbers are not reduced. If Salmonella or B. cereus multiplied at 8–9°C, cooling returns them to a dormant state, not a safe one. The infectious dose may already be present.
- Toxins are heat-stable. S. aureus and B. cereus toxins are not destroyed by reheating or chilling. Once formed, they remain.
Additionally, the manager cannot demonstrate how long the food was above 5°C - the log is missing. Under HACCP, the burden is on the business to prove control, not to assume it.
Correct action: Discard the affected food, document the disposal, and treat the event as a deviation requiring a corrective action record.
3. What monitoring and equipment changes would prevent this recurrence?
Read the worked answer
Monitoring:
- Install a continuous data logger in the walk-in chiller with alarms at 5°C; review the trend weekly.
- Record chiller temperatures at least twice daily (start and end of shift) and after any door-open event.
- Keep logs for the required retention period and make them available to inspectors.
Equipment and premises:
- Replace the torn door seal immediately; add a door-closing mechanism.
- Fit strip curtains or a self-closing door to reduce cold-air loss during deliveries.
- Separate raw and cooked/RTE storage - raw chicken must never share a chiller with RTE foods (cross-contamination risk).
Procedure:
- Schedule deliveries outside peak cold-room use, or use a separate receiving chiller.
- Train staff that a door propped open for 2 hours is a critical deviation, not a minor issue.
- Add a verification step: weekly review of logger data by the food safety officer.