Cold room failure during a Nairobi power cut
At 6:00 a.m. on a busy Saturday, a 60-seat restaurant in Nairobi loses mains power. The backup generator fails to start. The walk-in cold room was at 2°C when the outage began and reaches 13°C by 11:00 a.m. Inside are 18 kg raw chicken delivered the previous afternoon, 10 kg cooked beef stew cooled overnight, 8 kg cooked rice from Friday evening, and 6 L milk for the weekend buffet. The chef wants to move everything to the freezer, which is also warming, or cook the chicken immediately for the lunch service. No public health officer is available until Monday. The restaurant has a temperature log showing the cold room was 3°C at 10:00 p.m. on Friday. Staff have a probe thermometer but no ice. The manager asks you, as the senior food handler, to decide what can be kept, cooked, or discarded before the lunch rush at 12:30 p.m.
1. Rank the four items from highest to lowest risk and state what you would do with each. Show the time-temperature reasoning.
Read the worked answer
Use the temperature log and the 2-hour/4-hour principle. The cold room was 3°C at 22:00 Friday and 2°C at 06:00, then rose to 13°C by 11:00. That is five hours of warming, with an unknown period above 5°C, probably more than four hours. Rank by risk:
- Milk - ready-to-eat liquid, no kill step, supports bacterial growth. Discard.
- Cooked rice - ready-to-eat, Bacillus cereus risk. Discard.
- Cooked beef stew - ready-to-eat. Even rapid reheating to 75°C will not destroy heat-stable staphylococcal toxin if it formed. Discard unless you can prove it stayed below 5°C, which the log does not.
- Raw chicken - intended for cooking, but cumulative abuse is over four hours. Discard rather than serve.
If the chicken had been above 5°C for less than two hours, you could cook it immediately to 74°C and serve without delay. At five hours, that option is gone. Do not move food to a warming freezer. Record decisions and temperatures.
2. The chef argues that cooking the chicken to 75°C makes it safe. Evaluate this argument.
Read the worked answer
Cooking to 75°C kills Salmonella, Campylobacter and most vegetative cells, but it does not destroy preformed toxins or spores. For raw chicken, the main risk is bacterial survival, so thorough cooking is a valid kill step only if the meat has not been temperature-abused for more than four hours. Here the chicken has been in the warming room since 06:00 and the room reached 13°C. By 11:00 the cumulative time above 5°C is about five hours. The 2-hour/4-hour rule says: under 2 hours, use immediately; 2 to 4 hours, use immediately and do not re-chill; over 4 hours, discard. The chef's argument fails on the time criterion, not on the cooking temperature. The chicken may also cross-contaminate surfaces during the lunch rush. Decision: discard and document. If the outage had been shorter, cook to 74°C core, serve immediately, and do not cool and reheat.
3. Write three corrective actions to prevent recurrence at the next outage.
Read the worked answer
- Temperature monitoring and alarm: fit a data logger with an audible or SMS alarm on the cold room, check it before opening, and keep a written log. A probe thermometer alone is not enough if nobody checks it.
- Emergency procedure: write a one-page outage plan that names who decides, when to discard, how to use ice or gel packs, and how to keep doors closed. Stock the kitchen with ice packs and insulated boxes.
- Equipment and stock control: put the generator on a service contract with a weekly test, and reduce stock levels before weekends or known power interruptions. Keep raw and ready-to-eat foods separate so a failure does not contaminate cooked food. Train all handlers on the 2-hour/4-hour rule and give them authority to discard.