Food Safety, Hygiene and Preservation
Hazards and illness
Food hazards are biological (bacteria, viruses, parasites, moulds), chemical (pesticide residues, aflatoxins, heavy metals, cleaning agents) and physical (glass, stones, hair). A food-borne infection results from eating live organisms; a food intoxication results from a toxin already formed in the food, as with Staphylococcus aureus, Clostridium botulinum and Bacillus cereus.
Core safety rules
- Keep food out of the danger zone of 5–60 °C; hot food above 60 °C, cold food below 5 °C, freezer at −18 °C.
- Follow the two-hour rule for perishables at room temperature; reheat thoroughly to about 74 °C and only once.
- Separate raw and cooked foods, boards and knives; wash hands and utensils; use safe water; cover food.
- Store dry foods cool and dry, use first in, first out, and discard swollen cans and mouldy grain.
Preservation principles
Control moisture (drying, solar drying), temperature (refrigeration, canning, pasteurisation, UHT), pH (pickling with vinegar), osmotic pressure (salting, sugaring), oxygen (vacuum, aseptic packaging), and use permitted preservatives such as sodium benzoate and sulphur dioxide. Standards and systems include FSSAI, HACCP, Agmark and FPO marks.
Worked example
Cooked rice is left on the counter overnight and reheated for breakfast. Reasoning: Bacillus cereus spores survive cooking, germinate at room temperature and form a heat-stable toxin; reheating kills vegetative cells but not the toxin, so illness still follows. The correct answer is refrigeration within two hours, not longer reheating.
Traps that cost marks
Freezing stops bacterial growth but does not sterilise food. Scraping mould off soft food does not remove mycotoxins. Repeatedly reused frying oil produces trans fats and harmful oxidation products.