A hazard is anything that can make food unsafe. There are four main groups: biological, chemical, physical and allergens (covered in the last lesson). Knowing them helps you understand why the hygiene rules exist.
Biological hazards
These are the most frequent: bacteria, viruses, parasites and fungi.
Bacteria multiply very quickly when they have four things: food (especially rich in protein and moist), moisture, time and temperature. The Código de Boas Práticas para a Restauração (AIHSA), a sector guide, says they grow between 5 °C and 63 °C, with the maximum near 37 °C. This is the danger zone.
The best-known agents:
- Salmonella: raw eggs, poultry and raw meat. It is killed by cooking, but passes easily from raw to cooked food.
- Listeria monocytogenes: grows even in the fridge. It turns up in fresh and soft cheeses, cured meats, smoked fish and ready-to-eat food. It is dangerous for pregnant women, older people and people with weakened defences.
- Campylobacter: raw poultry.
- Staphylococcus aureus: lives on the skin, in the nose and in wounds. It produces a toxin that heat does not destroy.
- Bacillus cereus: cooked rice and pasta left at room temperature. The spores survive cooking and so does the toxin.
- Clostridium perfringens: meat cooked in large quantities and cooled slowly.
- Norovirus and hepatitis A virus: pass from the hands of infected people to food, or come from contaminated water and shellfish. Viruses do not multiply in food, but a few are enough to make you ill.
- Anisakis: a fish parasite. For fish eaten raw or almost raw, Regulation (EC) No 853/2004 requires operators who place it on the market to freeze it at -20 °C, throughout the whole mass, for at least 24 hours (or at -35 °C for at least 15 hours).
Symptoms and who is most at risk
Vomiting, diarrhoea, stomach pain and fever are common signs. They can appear hours or days after the meal, so it is hard to link the illness to the food. Small children, older people, pregnant women and people with weakened defences can become seriously ill from doses that a healthy adult would withstand.
Chemical hazards
- Residues of detergents and disinfectants on utensils and surfaces.
- Cleaning products stored next to food or in food containers.
- Histamine in fish such as tuna, mackerel and sardines, when they have been badly stored. Heat does not destroy it.
- Biotoxins in bivalves from areas contaminated by toxic algae.
Physical hazards
Fragments of glass, metal, plastic, wood, stones, bones, hair, nails, plasters and jewellery. A foreign body can break a tooth or injure the throat.
Cooking does not always solve it
Cooking well kills most bacteria, but does not destroy all toxins or all spores. That is why you must avoid leaving food in the danger zone for long. The WHO's five keys to safer food sum up prevention: keep clean, separate raw and cooked, cook thoroughly, keep food at safe temperatures and use safe water and raw materials.
Key points
- Danger zone: 5 °C to 63 °C.
- Listeria grows in the cold; the toxins of Staphylococcus and Bacillus resist heat.
- Viruses arrive mainly on hands.
- Risk groups deserve extra care.