PREVRA How to Calibrate a Thermometer: Ice-Point and Boiling-Point Methods Explained
A step-by-step poster showing both calibration methods for probe thermometers. Required weekly under SFBB. An uncalibrated thermometer gives false readings that can mask dangerous temperature abuse.
Why thermometer calibration is non-negotiable for food safety
An uncalibrated probe thermometer is worse than no thermometer at all. It gives you false confidence. If your probe reads 75°C but is actually 4°C out, you may be serving chicken that only reached 71°C — below the legal safe cooking temperature. Every temperature-based food safety decision you make depends on your thermometer being accurate.
The counter-intuitive fact: digital probe thermometers drift out of calibration more often than cheap bimetal dial thermometers. Digital probes are more precise when calibrated, but their electronic sensors are susceptible to drift from battery degradation, impact damage, and thermal shock. A good bimetal thermometer that has not been dropped can hold calibration for years. Check both types weekly regardless.
SFBB Safer Food Better Business requires weekly calibration checks with records kept. Your EHO will ask to see your calibration log. If you cannot produce it, every temperature record you have ever kept becomes questionable in their eyes.
Using this calibration guide in your kitchen quality control
Display this poster near your probe thermometer storage location. The ice-point method (0°C) is the most practical for daily kitchen use: fill a container with crushed ice and water, stir, insert the probe without touching the container sides, and wait for the reading to stabilise. It should read 0°C ±0.5°C.
The boiling-point method (100°C) provides a second calibration point but requires adjustment for altitude — water boils at approximately 98.5°C in some UK upland locations. Both methods together give you confidence across the full temperature range. Log every calibration in your digital SFBB system so you have an unbroken record of thermometer accuracy verified weekly.
Calibration errors that invalidate your checks
Using ice cubes straight from the freezer without adding water. Dry ice is below 0°C and will give a false low reading. You need a slurry — crushed ice with just enough water to fill the gaps — to achieve a stable 0°C reference.
Calibrating immediately after the thermometer has been in hot or cold food. Thermal shock causes temporary sensor drift. Let the probe stabilise at room temperature for at least 5 minutes before calibrating.
Assuming a thermometer that passes calibration does not need cleaning between uses. The probe tip carries bacteria from one food to another. Clean and disinfect the probe with an alcohol wipe between each use AND after calibration — the ice-water slurry is not sterile.
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