Thermometer calibration, Food Safety Glossary

Checking and adjusting a food thermometer against known temperatures so its readings stay accurate. Thermometer calibration is the process of checking a food thermometer against known reference temperatures, and adjusting it if needed, so its readings can be trusted. A probe thermometer can drift out of accuracy over time through normal use, knocks or battery changes. If a thermometer reads incorrectly, staff might believe food is safely hot or cold when it is not, so calibration is essential to reliable temperature control. The Australia New Zealand Food Standards Code requires food businesses handling potentially hazardous food to have a temperature measuring device accurate to plus or minus 1 degree C. Calibration is how a business confirms the device still meets that accuracy. It underpins every other temperature check, because monitoring cooking, cooling, reheating and holding is only meaningful if the thermometer itself is accurate. The two common calibration methods are the ice-point method and the boiling-point method. For the ice point, the probe is placed in a slush of crushed ice and water, where it should read 0 degrees C. For the boiling point, it is placed in boiling water, where it should read close to 100 degrees C at sea level. If the reading is outside plus or minus 1 degree C, the thermometer is adjusted where possible or taken out of use and replaced. Australian businesses calibrate their thermometers on a regular schedule and also after any event that could affect accuracy, such as dropping the probe. The checks are usually recorded, so the business can show an environmental health officer that its temperature readings are reliable. Calibration is a typical verification activity within a food safety program. A restaurant calibrates its probe thermometer each month using the ice-point method. Staff fill a cup with crushed ice and a little water, insert the probe without touching the sides, and wait for a stable reading. It shows 0.5 degrees C, within tolerance, so they record the check as a pass and keep using the thermometer.