Food Safety Hazards and Contamination
The four hazard types
Candidates must be able to sort hazards into microbiological (bacteria, viruses, moulds, parasites), physical (glass, metal, hair, insects, packaging), chemical (cleaning chemicals, pesticides, pest bait, unlabelled decanted liquids) and allergenic (the 14 regulated allergens). Exam questions often describe a scenario and ask which category applies - read the object, not the outcome. A blue plaster in a sandwich is physical; a peanut in an unlabelled cake is allergenic.
How contamination happens
Learn the routes: hand-to-food, food-to-food (raw meat dripping onto ready-to-eat salad), equipment-to-food, pest-to-food, soil/water-to-food and airborne droplets. Cross-contamination from raw to ready-to-eat food is the single most examined route.
Bacterial growth conditions
Bacteria need food, moisture, warmth and time. The danger zone is 5°C to 63°C; the optimum for most pathogens is around 37°C. Clostridium perfringens and Bacillus cereus are spore-formers linked to cooked rice and reheated meat; Salmonella to raw poultry and eggs; Listeria to chilled ready-to-eat foods and grows at refrigeration temperature; E. coli O157 to undercooked mince and unpasteurised dairy. Spores survive cooking, so slow cooling and bulk reheating are the traps.
Traps and a worked example
Watch for questions that ask what kills bacteria versus what merely stops growth - cooking kills; chilling only slows. Also watch 'food poisoning vs food-borne illness': toxins can be present with no live bacteria.
Worked example: A caterer cools a large pan of stew on the worktop for five hours. Rule of thumb: cool food within 90 minutes and refrigerate; bulk cooling on a worktop keeps food in the danger zone and lets spore-formers multiply.