Thermometers are vital tools in food service. You need them to cook, cool, hold, and reheat food safely. A thermometer that is even five degrees off can lead you to sell or serve food that is not safe to eat.
But you can only rely on a thermometer if you calibrate it often. Exactly how often depends on the type of thermometer.
Calibrating your food thermometer is easy. Just follow these three steps:
- Test your thermometer’s accuracy using the boiling point method or the freezing point method
- Adjust your thermometer
- Recalibrate your thermometer often
Test your thermometer’s accuracy
To calibrate a thermometer, you must first test its accuracy in a substance with a known temperature. Then you’ll adjust the thermometer to match that temperature.
There are two common methods for thermometer calibration in food service: the boiling point method and the freezing point method.
Boiling point method
If you often use your thermometer with hot foods, you may want to use the boiling point method when calibrating your thermometer. Remember that water boils at different temperatures depending on the altitude. To use this method, you need to know the boiling point of water in your area. It’s generally between 190 and 212°F (88–100°C).
Once you know the boiling point, heat a pot of water. When it has reached a rolling boil, insert a thermometer into the water. Make sure the entire sensing area is submerged, but don’t touch the pot with the thermometer. Wait for the temperature reading to stop changing. If the temperature reading does not match the boiling point, adjust it without taking it out of the water.
This thermometer calibration procedure can be dangerous to use. Take care not to burn yourself as you’re calibrating a thermometer. The Food Safety and Inspection Service recommends clipping the thermometer into the stem sheath. You can hold the sheath horizontally to lower the thermometer into the water.
Freezing point method
The freezing point method, also known as the ice point method, might be the easiest way to calibrate your thermometer. If you often use your thermometer to take the temperature of cold foods, use this method.
Start by filling a glass with ice water. Let the water sit for a couple minutes so the temperature settles at 32°F (0°C). Then immerse your thermometer in the water. Don’t let the thermometer touch the cup. Wait for the temperature reading to stabilize and keep it in the cup as you adjust it.
Although this method is less dangerous than the boiling point method, you may still want to clip the thermometer to its stem sheath. Hold the sheath horizontally to keep the thermometer in position as you lower it into the water.
Adjust your thermometer
Your thermometer should be accurate within 2°F (1°C). If you notice a bigger gap after testing the thermometer’s accuracy, you need to adjust it.
If you cannot calibrate an inaccurate thermometer, you should replace it. Your business may receive inspection violations for using inaccurate thermometers.
Because each thermometer is different, the best way to learn how to calibrate your thermometer is to consult the instructions that came with it. Below, we’ve included general instructions for calibrating three common thermometer types.
If you have a bimetal thermometer, look for a calibration nut beneath the display dial. You may need a wrench or pliers to turn the nut.
To calibrate a digital thermometer, look for the reset button. If the thermometer does not have a reset button, you may not be able to calibrate it. Check the instructions that came with the product for details.
Some liquid-filled thermometers can be calibrated by moving the thermometer stem inside the holder. Check the product instructions for more information.
Recalibrate your thermometer often
A calibrated food thermometer is vital to your ability to prepare and serve safe food. Make sure to test your thermometer often to make sure it stays accurate.
The exact calibration schedule depends on the type of thermometer you use and how you use it. The following are some guidelines for when you should recalibrate your thermometers.
- In general, you should calibrate bimetal thermometers before every single shift.
- Calibrate digital thermometers every week or month.
- Always calibrate new thermometers or a thermometer that has been dropped.
- It’s also a good idea to calibrate a thermometer after using it to measure significantly different temperatures.
- For best results, follow the manufacturer’s instructions.
Now you know how to calibrate a thermometer! For more food safety tips, check out our food handler training.
— Katie Heil