Food safety: hazards
Food safety means food will not harm us when we make, store and eat it. Anything in food that can harm us is a hazard.
- Biological: germs such as bacteria, viruses, moulds and parasites. They cause food poisoning.
- Chemical: too much pesticide, cleaning liquid, harmful additives, toxins made by mould.
- Physical: stones, glass, metal bits, hair.
- Allergens: foods like peanut, milk, egg, wheat that can harm a person who is allergic.
Germs can double every 20 minutes in warm food. One germ becomes 8 in 1 hour and 64 in 2 hours.
Food hygiene
Hygiene means clean habits that keep germs away from food.
- People: wash hands with soap, cover cuts, wear a clean apron and hair cover, stay home when ill.
- Place and tools: clean floors, boards and knives. Keep raw and cooked food apart. Keep pests out.
- Food: cook well (centre at least 75 °C), chill fast, use clean water.
- Factories follow Good Manufacturing Practice (GMP) and HACCP, a plan that finds the key points where a hazard could enter and checks them.
Food preservation and storage
Preserving food stops germs growing. The main ways: cold (fridge 0–5 °C, freezer −18 °C), heat (boiling, canning, pasteurising), drying, salt or sugar, acid (pickles), smoke and permitted preservatives. Keep the danger zone (5 to 60 °C) in mind: do not leave cooked food there for more than 2 hours. For the full list of methods, see the lesson Food preservation.
Food packaging
A pack has four jobs: protect (from germs, dirt, air, light, water and knocks), contain (hold a fixed amount), inform (carry the label) and make life easy (easy to carry, open and store).
- Glass: does not react with food, can be reused; heavy and breaks.
- Metal cans: strong, airtight, good for heat treatment.
- Paper and card: light, printable, usually with a lining.
- Plastic films and bottles: light, cheap, flexible; need recycling.
Special packs: vacuum (air removed), modified atmosphere (air replaced by a gas such as nitrogen) and tamper-proof seals that show if a pack was opened.
Quality labelling: how to read a food label
Rules differ a little between countries, but good labels usually show:
- Name of the food.
- Ingredients, listed with the heaviest first.
- Allergens clearly marked.
- Net quantity (for example 400 g).
- Nutrition facts per 100 g or per serving (energy, fat, sugar, salt, protein).
- Date: use-by is a safety date (do not eat after it); best-before is a quality date (food may be safe but less good after it).
- Storage advice, batch number and maker's name and address.
- In India a green dot marks vegetarian food and a brown dot non-vegetarian food, and packs show the FSSAI licence number.
Quality marks and standard marks (such as quality-standard certificates) show that the product follows a set standard.
Try it
Take any packet from the kitchen. Find: the name, the first ingredient (is it the main one?), allergy words, net quantity, and the date. Is it use-by or best-before? Then in the 3D move the day slider past the use-by day and see what happens.
Key formulas and definitions
- Germs double about every 20 min: count = start × 2^(time ÷ 20 min)
- Nutrient in pack = (amount per 100 g ÷ 100) × pack weight
- Days left = use-by day − today
- Safe fridge ≤ 5 °C; freezer −18 °C; cook centre ≥ 75 °C
Worked examples
1. A curd pack is made on day 0 and its use-by is day 6. Today is day 4. How many days are left?
Days left = 6 − 4 = 2 days.
2. One germ doubles every 20 minutes in warm food. How many germs after 2 hours?
2 hours = 120 min = 6 doublings. 2^6 = 64 germs.
3. A snack has 5 g fat per 100 g. The pack weighs 400 g. How much fat is in the whole pack?
(5 ÷ 100) × 400 = 20 g.
Common mistakes
- Mixing use-by and best-before. Use-by is about safety; best-before is about quality.
- Thinking the fridge kills germs. It only slows them; cooking kills them.
- Reading only the front of the pack and ignoring the ingredient and allergy list.
- Buying dented, bulging or torn packs. The wall is broken, so dangers may be inside.