Microbiological, Chemical and Physical Food Hazards
Hazard types
A hazard is anything that can make food unsafe. Microbiological hazards include bacteria, viruses, moulds, yeasts and parasites. Chemical hazards include cleaning chemicals, sanitisers, pesticides, lubricants, allergens and toxins. Physical hazards include glass, metal, plastic, bone, stones, pests, jewellery and plasters. The exam tests whether you can classify a scenario and choose the right control.
Microbiological detail
- Key foodborne bacteria include Salmonella, Campylobacter, E. coli O157, Listeria monocytogenes, Staphylococcus aureus, Bacillus cereus, Clostridium perfringens and Clostridium botulinum.
- Bacteria need food, moisture, suitable acidity, time and a favourable temperature. Some need oxygen; Clostridium species grow without it.
- Spores survive normal cooking. Bacillus cereus in cooked rice and Clostridium perfringens in stews are classic examples.
- Some toxins are heat-stable, so reheating does not make food safe. Staphylococcus aureus toxin and Bacillus cereus emetic toxin are examples.
- High-risk foods include cooked meat and poultry, dairy, eggs, seafood, cooked rice and pasta, gravies and ready-to-eat products.
Chemical and physical controls
Store chemicals in labelled original containers, never in drinks bottles or food tubs, and away from food. Use only food-safe lubricants. Control allergens through separation, clean equipment and accurate ingredient information; EU law lists 14 major allergens. For physical hazards, use detectable plasters, cover cuts, avoid jewellery, inspect equipment and follow a glass-breakage procedure.
Worked example
Cooked rice is left in a warm kitchen overnight, then reheated for service. Bacillus cereus spores survive cooking, and slow cooling lets them grow and produce an emetic toxin. Reheating to 75°C kills vegetative cells but not the toxin, so the rice can still cause vomiting. The control is to cool rice quickly, refrigerate it, reheat once to 75°C and discard rice held above 5°C for too long.
Traps
- Believing reheating destroys all toxins.
- Thinking all bacteria need oxygen.
- Decanting cleaning chemicals into unlabelled bottles.
- Ignoring allergen cross-contact because a food 'contains only a trace'.