Principles of Food Safety — Buying, Storing and Preparing
Temperature: The Most Important Food Safety Control
If you could only remember one food safety principle, it would be this: temperature controls bacterial growth. The Food Standards Agency (FSA) publishes specific temperature guidelines that underpin every aspect of safe food handling, and the written paper tests exact figures. Vague answers like “keep it cold” or “cook it until hot” will not earn marks. Memorise these numbers.
FSA temperature guidelines: Freezing: –18°C — bacteria cannot multiply. Chilling: 0 to below 5°C — bacterial growth is very slow. Danger zone: 5 to 63°C — bacteria multiply rapidly. Cooking and reheating: 75°C — most harmful bacteria are destroyed.
The temperature danger zone is the range 5°C to 63°C. This is why food should never be left at room temperature (typically 18–22°C, well inside the danger zone) for longer than necessary. Bacteria can double in number every 20 minutes at room temperature — a portion of cooked rice left on a worktop for two hours can contain many millions more bacteria than one put straight into the fridge.
Buying and Storing Food Safely
Safe food handling begins at the point of purchase, not when you get home. When shopping, always:
- Check date marks before buying. ‘Use by’ dates apply to high-risk foods such as raw meat, cooked meat products and soft cheeses — consuming after this date could harm health. ‘Best before’ dates apply to lower-risk foods such as tinned goods, dried pasta and frozen peas; the food remains safe after this date but may decline in quality.
- Pack raw meat and fish in separate bags from ready-to-eat foods to prevent drip contamination.
- Choose chilled and frozen foods last in a supermarket shop and transport them in insulated bags to minimise the time spent in the danger zone.
‘Use by’ is a food safety date. Eating food after its use-by date is a genuine health risk, regardless of whether it looks or smells fine — harmful bacteria do not always cause visible or olfactory changes. ‘Best before’ is a quality date. After a ‘best before’ date, the food may be less flavoursome, have a different texture or lose some nutritional value, but it is not automatically unsafe. A can of tomatoes three days past its best-before date is still safe to eat; a pack of cooked prawns one day past its use-by date should be discarded. In an exam, be precise: low-risk ambient foods carry ‘best before’ labels; high-risk perishable foods carry ‘use by’ labels.
At home, correct use of domestic refrigerators and freezers is essential:
- Fridges should run at 0 to below 5°C. Many domestic fridges are set too warm; an internal thermometer is a good investment.
- Raw meat and fish should be stored on the bottom shelf of the fridge in sealed containers to prevent drip onto cooked or ready-to-eat foods below.
- Freezers should run at –18°C. Food is safe indefinitely in a correctly operating freezer, although quality declines over time.
- Ambient foods — dry goods such as flour, rice, tinned goods, pasta and breakfast cereals — should be stored in sealed containers in cool, dry, ventilated cupboards away from direct sunlight and damp. Ambient storage prevents moisture absorption (which could allow mould and bacterial growth) and pest contamination.
- All open or partially used foods should be covered. Covering prevents contamination from airborne bacteria, insects and dust, and reduces moisture loss from chilled foods.
Raw meat and fish must be stored on the bottom shelf of the fridge in sealed containers to prevent bacterial cross-contamination from drips onto ready-to-eat foods. The fridge must run at 0 to below 5°C — not at room temperature or “just cold enough”.
Personal Hygiene and Preventing Cross-Contamination
Cross-contamination is the most common route by which bacteria from raw food reach ready-to-eat food. Safe food preparation requires vigilance at every stage:
- Personal hygiene: Wash hands thoroughly with soap and warm water for at least 20 seconds before handling food, after handling raw meat or fish, after visiting the toilet, after touching the face or hair, after handling waste, and after touching pets. Cover cuts and wounds with blue waterproof plasters (blue so that if they fall into food, they are visible).
- Clean work surfaces: Wipe surfaces with antibacterial cleaner between tasks. A damp cloth is not sufficient — it spreads bacteria. Use paper towels or a freshly laundered cloth.
- Separate raw and cooked foods: Use separate chopping boards and knives for raw meat/fish and for ready-to-eat foods. Colour-coded systems (e.g. red boards for raw meat, green for vegetables, yellow for cooked meat) reduce the risk of confusing equipment.
- Defrosting: Defrost frozen foods thoroughly in the fridge, not at room temperature. Defrosting at room temperature means the outer layers of the food spend time in the danger zone while the centre is still frozen. Large items such as a frozen chicken need 24 hours in the fridge per kilogram. Cook food promptly after defrosting; do not refreeze unless it has been cooked first.
Cooking food to 75°C throughout destroys most harmful bacteria, including campylobacter and salmonella. The critical word is “throughout” — the surface of a chicken breast may be 75°C while the thickest part near the bone is still below 60°C. A food temperature probe inserted into the thickest part of the meat is the only reliable way to check that the correct temperature has been reached. Visual checks (looking for clear juices, no pink meat) can be used alongside a probe but are not sufficient alone, especially for large poultry pieces or rolled joints. After use, the probe must be cleaned and sanitised before being used on another food to avoid cross-contamination.
When reheating food, it must also reach 75°C throughout. Food should only be reheated once — multiple reheat cycles increase the time food spends in the danger zone and raise the risk of bacterial growth. Rice is a particular concern: cooked rice that has been cooled quickly and refrigerated within two hours can be reheated safely once; rice that has been left at room temperature is a high-risk food because of the risk of Bacillus cereus toxins (though this specific bacterium is not on the specification, the principle of prompt cooling and reheating applies to all cooked grains and protein-rich foods).
High-risk foods — cooked poultry, egg dishes, shellfish, soft cheeses and cooked rice — require particular attention throughout the buy, store, prepare, cook and serve chain. Every stage at which these foods could enter the temperature danger zone or be exposed to raw food represents a contamination risk that must be actively managed.