Temperature readings play a key part in food preparation and manufacturing standards. You can’t accurately tell if food is safely cooked by looking at it, smelling or tasting it. Nor can you safely assess if food that’s being kept hot for serving, or buffet food, hasn’t fallen in to the danger zone without checking its temperature. It’s critical the thermometers used in your process are accurately calibrated as fluctuations in temperature during any stage of processing can cause issues with food safety, hygiene and overall quality.
Two things to do before using a food thermometer:
1) Check it / test it. You can use boiling or ice water to verify how accurate your thermometer is.
2) Adjust or calibrate it. If the readings do not match 100 or zero, your thermometer will require an adjustment (or calibration).
How to verify a food thermometer in-house
Two of the most common methods used in-house to check the accuracy of food thermometers are the boiling water and ice water methods. Both of these methods are very quick and easy to perform and provide instant results.
Verifying in boiling water: Place the probe of your food thermometer in boiling water and check the reading. The reading should be 100 degrees Celsius.
Verifying in ice water: Place the probe of your food thermometer in iced water and check the reading. The reading should be zero degrees Celsius.
Once you’ve performed the verification, make sure you record it. These records will be reviewed as part of any third-party HACCP certification or quality audit. Record the thermometer ID or tag number, the test results and the person or company who completed the test.
Some businesses have the capability to do this in-house, while others send their equipment to an external calibration provider. You’ll need to adjust the thermometer based on your test, in order to get an accurate temperature reading.
How to calibrate a food thermometer in-house
Your food thermometer’s instructions should tell you how to do this, as it varies between types and models. Usually, there’s a small nut under the temperature dial that allows the thermometer to be adjusted. If you use digital thermometers, most models have a reset button that should make it accurate again.
Why is it important to calibrate a food thermometer?
Performing frequent calibrations on your thermometers ensures the equipment performs at optimum levels. This in turn reduces the risk of error and provides accurate, traceable and repeatable measurements throughout the production or preparation process.
Having accurate results at every stage of production can help avoid potential recalls due to ‘bad’ batches. And, as a worst-case scenario can prevent the production of a product that may kill a consumer – a devastating outcome for any food business.
How often should I calibrate my food thermometer?
It is down to individual businesses to decide how frequently they calibrate their thermometers.
Usually the decision is made based on factors such as how often the thermometer is used within the production process and how big the risk is if the thermometer was to display an inaccurate reading.
Other factors such as the legal or regulatory requirements governing the industry, or customer stipulations may also be considered.
The best practice approach we recommend to our customers is to run a quick calibration in-house on a daily basis to ensure your thermometers are performing correctly. Additionally, we recommend sending your thermometers to an external calibration supplier for a more thorough calibration once a year.
How to perform an annual food thermometer calibration
No matter which method you choose for your daily in-house verifications, it is best practice to send your thermometers to an external calibration provider annually for a more thorough calibration.
External calibration providers will use methods such as calibration through immersion, where probes are placed into a metrology well alongside a reference probe and subjected to various temperatures over the range of use. Another, less common, calibration method is calibration in air, where the probe under test is placed into an environmental chamber alongside a reference probe and subjected to various temperatures over the range of use. These methods allow multiple temperature points to be checked within a range from -45ᵒC to 660ᵒC, giving you a higher degree of accuracy than the self-verification method.