Thermometers and calibration

Every temperature check depends on the thermometer. If it is wrong, every record made with it is wrong too.

Use a digital probe thermometer suitable for food. Clean and disinfect the probe before and after each use, especially between raw and ready-to-eat food. Keep a spare, and spare batteries. Put the tip in the centre or thickest part of the food. Do not let it touch the pan or tray. Do not use glass thermometers in food areas.

Check accuracy regularly. Many businesses do this monthly, and more often if a probe is used heavily. Put the probe in iced water. It should read −1°C to +1°C. Then put it in boiling water. It should read 99°C to 101°C. Wait for the reading to settle, and take care with the boiling water. Also check a probe after it has been dropped or repaired.

If a reading is outside these limits, stop using the probe. Label it, and replace it or have it calibrated. Then think about what it was used for since the last good check. Suppose a probe reads 5°C too high. A chicken recorded at 75°C may have reached only 70°C for a few seconds. Decide what this means for food that is still in stock, and record what you did.

Keep a simple calibration record for each probe: the date, both readings, who did the check and any action taken. Give each probe a number, so that you can match records to it. Check the built-in displays on fridges, freezers and hot-holding units against a checked probe too, because they can drift over time.