Food Safety: Hazards, Temperature Control and HACCP
The three hazard families
Every food safety question starts by classifying the hazard. Biological hazards are bacteria, viruses, parasites and moulds; they cause most foodborne illness. Chemical hazards include cleaning agents, pesticides, unapproved additives and allergen cross-contact. Physical hazards are foreign objects such as glass, metal fragments, bones, plasters and packaging. A common exam trap is naming a hazard by its symptom or by the food involved rather than by its category.
The temperature danger zone
Bacteria multiply fastest between 5 °C and 63 °C (41–145 °F), with the optimum near 37 °C. Keep high-risk foods below 5 °C or above 63 °C. The two-hour/four-hour rule is a reliable rule of thumb: food held in the danger zone for under 2 hours may be chilled or used; 2–4 hours it must be used immediately and not returned to refrigeration; over 4 hours it must be discarded. Reheating must reach 75 °C at the core. Cooling should take food from 63 °C to 5 °C within 90 minutes to 6 hours depending on local code - always quote the code you are taught.
HACCP in seven steps
Conduct a hazard analysis; determine critical control points (CCPs); set critical limits; monitor them; establish corrective actions; verify the system; keep records. Questions often confuse a CCP with a control point: a CCP is a step where loss of control would make the food unsafe, and it must have a measurable limit.
Worked example
A chef cooks chicken curry at 80 °C, leaves it on the pass for 3 hours, then chills it. Under the four-hour rule the curry has spent 3 hours in the danger zone, so it may be served immediately but must not be chilled and re-sold. Correct action: reheat once to 75 °C and serve, or discard.
Traps to watch
Cross-contamination via boards and cloths; handwashing duration and technique; the difference between cleaning and sanitising; allergen declaration duties; pest control signs (droppings, grease marks, gnawed packaging).