Food safety

All about calibration process I How to calibrate thermometer?

Thermometer calibration is an important operation that reconfigures the temperature readings of the device to become ...

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  • Thermometer calibration is an important operation that reconfigures the temperature readings of the device to become accurate after use.
  • Many food safety operations rely on accurate temperature readings.
  • The two most common thermometer calibration methods are boiling point and freezing point methods. 

An accurate food thermometer plays a very significant role in maintaining food safety in any food establishment. Whether for low-temperature storage or thorough cooking, accurate temperature readings are significant. The safety of the food being cooked or stored depends on the accuracy of your thermometer as these operations rely on hitting or maintaining target temperatures, respectively. 

how to calibrate thermometer


Thermometers are very common kitchen equipment and they are used almost every day during service. With frequent use, thermometers lose their accuracy over time and would need to be calibrated. The frequent use and sudden significant changes in temperature readings affect the device and often cause mild or significant offsets. As such, thermometer calibration must be regularly performed.

Many other food safety operations are dependent on temperature readings. With an inaccurate thermometer, the purpose of these operations becomes insignificant and defeated. Food safety hazards, particularly pathogens, may survive and continue to grow if the target temperature reading is off by a few degrees. Such reasons make thermometer calibration an important part of food safety operations. No need to worry because this task is easy and does not take too long.

In this article, learn about the different ways how to calibrate your thermometer and why is it important to do so.


What is thermometer calibration?

Thermometer calibration refers to the process of reconfiguring a thermometer for it to produce more accurate readings. Thermometers, like other equipment, fall out of their standard specifications due to frequent use or time. Inaccurate thermometers can result in misleading results. These results can cause over or under-processing which can be significant for the safety or the quality of the food product. 

Food safety operations such as chilling, cooking, and holding are temperature-dependent. For example, different types of meat require a particular target internal temperature that will render the final product safe from food safety risks. An example would be the case of Salmonella, a well-known pathogen associated with poultry.

This pathogen is readily inactivated only at temperatures equal to or higher than 165°F (74°C). These target internal temperatures are based on the most effective temperature in eliminating pathogens. They can only be effective if hit within a very narrow range. A few degrees below the target temperature will increase the risk of causing foodborne illnesses. 

Calibration can be different for each type of thermometer. Manufacturers and distributors often provide calibration instructions and kits to food businesses. Sometimes, they even give a demonstration of thermometer calibration. The calibration procedure for an instant-read digital food thermometer will surely be different from a common dial food thermometer. Food handlers must be well-trained on how to calibrate a thermometer as this is a vital part of succeeding food safety operations.


Food Safety Management System


Why is thermometer calibration important?

The significance of thermometer calibration in the food industry goes beyond food safety. This operation helps your food business maintain stable operations, increase efficiency, and run clear of food-related issues. When done at regular intervals, thermometer calibration can save your team a lot of time and continuously grow your market by gaining consumer confidence in your food safety practices and services. 


Specifically, thermometer calibration can help you achieve the following advantages:

  • Food safety assurance. As we have mentioned, some food safety operations are dependent on correct temperature readings. When accurate temperature measurements are achieved, food safety is secured and the risk of causing any foodborne illness is significantly reduced. In addition, the thermometer calibration procedure is an integral part of a corrective action plan of a HACCP food safety plan. When sudden spoilage occurs because of a potential equipment malfunction, thermometer calibration must be immediately performed. This is to check whether the malfunction originated from the wrong temperature settings because of an inaccurate thermometer.

  • Quality assurance. Proper calibration of the thermometer also ensures the delivery of consistent food quality. Especially for foods that can be served in different degrees of doneness such as steaks, a slight temperature difference can change the results. Some customers have a preference for eating well-done steak which is thoroughly cooked to the center and perfectly charred on the outside. This preferred degree of doneness can be achieved by targeting an internal safe temperature of 165°F (72°C). With an uncalibrated thermometer, the steak can become either undercooked or very tough to eat which can cause consumer dissatisfaction.

  • Cost-saving and produces more profit. Aside from preventing food safety issues such as customer complaints or lawsuits from occurring, proper and regular calibration can also help food businesses save money and gain more profit. By having a properly calibrated thermometer, store-wide shutdowns and service maintenance are effectively prevented. Performing these corrective procedures will hinder normal operations and will affect business performance. Thermometer calibration acts as a preventive measure in this instance. Additionally, operation efficiency is achieved when no further issues concerning temperature reading are detected during service hours.

  • Detection of problems with other equipment. A calibrated thermometer can help food handlers easily detect whether there is a problem with any equipment that uses it such as an oven or a refrigerator. In case of inaccurate or faulty reading, reactive maintenance can be applied as an on-the-spot calibration. When food handlers are confident that the thermometer represents accurate temperature readings, any significant drop or sharp increase in the temperature of equipment will alert them that it needs to be checked. 

As part of a HACCP plan, thermal calibration can be set as both preventive and corrective action. Calibration can be used to address recurring breaches of temperature critical limits during cooking. It can be used to detect further problems with the operation such as the need to send the oven to maintenance. On the other hand, regularly monitoring thermometer calibration is an integral part of a food safety management system.

Monitoring forms dedicated to this operation must be available and include information such as date, time, frequency, and results. It can help food businesses achieve compliance with significant food safety laws concerning any thermometer calibration standard. It can also create a seamless and uninterrupted flow of work operations for everyday services.

Read more about the temperature danger zone in food here.


How to calibrate a thermometer?

Thermometer calibration methods depend on the type of thermometer you use. Some thermometers come with a special kit used specifically to calibrate them, whereas some can be calibrated using general methods. More technical calibrations are often done by thermometer manufacturers themselves. They can either send a representative to perform the calibration on-site or have the thermometer sent back to them for custom thermometer calibration services. 

Here are two of the most common methods for thermometer calibration that you can perform for common thermometer types. These methods can be done every day or periodically to ensure that your thermometers are in top shape.


Thermometer calibration freezing point method


Freezing point method

Otherwise known as the ice point method, this technique is commonly performed for thermometers that are used to measure low temperatures. This method is performed as follows:

  1. Fill a glass or deep container that is large enough to accommodate the thermometer probe with crushed ice.
  2. Add distilled water or soft water into the glass and stir the ice water mixture.
  3. Submerge the thermometer probe up until the immersion mark without touching the bottom of the glass. Wait for at least 30 seconds or until the temperature reading becomes stable.
  4. If the thermometer does not read 32°F (0°C), use a wrench to adjust the calibration nut until the reading is correct.
  5. Reread the temperature of the ice water solution using the calibrated thermometer at least two to three times and record results on a logbook. Wash the thermometer with room temperature water in between readings.


Thermometer calibration boiling point method


Boiling point method

The boiling water method is used for thermometers that are utilized for measuring high temperatures. This method is performed as follows:

  1. Fill a deep pan or a glass beaker with distilled water and boil over medium heat.
  2. While the water is boiling, place a previously calibrated thermometer into the water and allow it to read the temperature. 
  3. After 30 seconds or once stable, place the thermometer being calibrated and read the temperature measurements. Do not let both thermometers touch the bottom of the pan or container.
  4. If the temperature readings are not the same, ideally  212°F (100°C), adjust the calibration nut or adjustment screw until the reading is correct.
  5. Reread the temperature of the boiling water using the calibrated thermometer at least two to three times and record results on a logbook. Wash the thermometer with room temperature water in between readings.

For both calibration methods, take note that the water to be used must be soft or distilled water. The impurities in hard water can significantly affect the accuracy of the thermometer reading. When the water is filled with impurities, the boiling point and freezing point of water are relatively higher and lower, respectively. Additionally, a reference or comparison thermometer can also be used for the freezing point method.

Any of the two calibration methods can be used along with a reference thermometer to calibrate non-adjustable thermometers. Reference thermometers are preferably NIST-certified (National Institute of Standards and Technology) thermometers. Make sure that the reference thermometer is accurately and recently calibrated.

Upon comparing the temperature readings, the non-adjustable thermometer can be labeled with an offset value of the degree difference to correct any temperature reading. That is if the reference thermometer reads 212°F (100°C) and the thermometer being calibrated reads 209°F (98°C), all temperature readings using the non-adjustable thermometer must be offset by  3°F or 2°C. 


How do you calibrate a digital thermometer?

Both boiling point and freezing point methods of calibration can be used to calibrate a digital meat thermometer. The only difference is that most digital thermometers have a calibration reset button and a digital display to reenter the correct temperature reading when compared with analog thermometers. Additionally, digital thermometers need to have their batteries checked and replaced. A set of exhausted batteries will most likely produce inaccurate or unclear temperature readings. More sophisticated digital thermometers may need to be sent to their manufacturers for a scheduled thermometer calibration.


How to test thermometer calibration?

To check the thermometer calibration, the chosen method must be performed two to three times and gain the same temperature reading. Only very small differences between calibration results are allowed to ensure the effectiveness of the calibration method. 


How do I know if my thermometer is accurate?

In addition to repeatedly recording temperatures using the calibrated thermometer, you can also use a previously calibrated thermometer as a reference. Submerge both thermometers in either an ice bath or in boiling water. If their temperatures are almost or exactly similar, then the thermometer is accurate.


When should I calibrate a thermometer?

Ideally, thermometers must be calibrated every day before starting your operations. This ensures that you are working with an accurate thermometer. Generally, a thermometer reading must only have a ±1°F or ±0.5°C difference from a reference thermometer. Any higher or lower reading than this calibration temperature range can significantly affect the results of concerned food safety operations.


Ideally, calibration must be performed during these instances:

  • When dropped (especially for dial thermometers)
  • When switching its use from extreme temperature ranges (freezing to boiling or vice versa)
  • Long storage time period
  • When the thermometer is new
  • When used multiple times in a day


All of these instances can create a significant difference in the degree of accuracy of measurements. Although, these instances are not exhaustive. That is, other situations can call for an immediate calibration. Food handlers are used to measuring temperature so that they can partly tell if there is something off about the temperature readings. As such, you can always perform a calibration whenever the results seem off.

During calibration, recordkeeping must always be practiced. All temperature readings during calibration must be recorded as proof of the accuracy of the performed calibration which can be used for a thermometer calibration report. This calibration document can be used to verify whether the problem with a critical control point concerns the temperature and proper corrective actions may be applied. 


using a calibrated thermometer


Factors to consider when calibrating a thermometer

During calibration training, you have to consider a few things during the orientation. These factors may make a significant difference and knowing them will prepare your kitchen staff for uncommon situations during calibration.


Below are a few things to consider when calibrating a thermometer:

  • Purpose of the thermometer. Often, it is suggested to use different thermometers for measuring hot and cold temperatures. The abrupt and significant changes in the temperature readings can cause significant discrepancies faster and would require calibration more often. The proper calibration method must also depend on the type of operations where the thermometer will be used. That is use the freezing point method for a thermometer used to measure low temperatures and boiling point for hot temperatures.
  • Changes in boiling temperature by elevation. The boiling point of water varies depending on the altitude of your location. The higher the elevation of your location, the lower the boiling point of water is. Below are the changes in boiling point temperatures of water depending on the level of elevation:

Sea Level: 212°F (100°C)

1,000 feet: 210°F (98.9°C)

2,000 feet: 208°F (97.8°C)

3,000 feet: 206.4°F (96.9°C)

4,000 feet: 204.5°F (95.8°C)

5,000 feet: 202.75°F (94.9°C)

8,000 feet: 197.5°F (91.9°C)

  • Purity of water used for calibration. As previously mentioned, any impurities such as minerals, dirt, or added components in water will affect its boiling and freezing points. The boiling point will become higher, whereas the freezing point lower. If impure water is used, it will result in inaccurate temperature readings and then wrong calibration decisions. Use distilled water to ensure that there will be no materials to affect the temperature readings.
  • Types of food thermometers. The appropriate calibration method for a thermometer can be dependent on its type. Digital thermometers have a few different settings or calibration operations when compared with a dial thermometer. Make sure to read the manufacturer's product instructions.

Learning how to calibrate a food thermometer must be part of a food handler's training routine. This is an operation that will need to be repeated many times to ensure food safety. In doing so, the mentioned factors and proper temperature measurement procedures must be highlighted during training.

In terms of choosing the type of thermometer to use for measuring high or low temperatures, dial thermometers can do both low and high-temperature readings. This type is very flexible and durable even if exposed to extreme temperatures. Digital thermometers are advisable for operations that will not expose the thermometer to very high heat. Unlike a dial thermometer, you cannot leave a digital thermometer stuck inside an oven. Use separate thermometers for measuring hot and cold objects.


Thermometer calibration as part of your HACCP plan

Proper and timely calibrating a thermometer is a great preventive step toward controlling food safety hazards. Many different operations that are meant to control or eliminate hazards vary in effectiveness depending on temperature. As such, the importance of gaining accurate measurements cannot be understated. Calibration can also be a part of corrective actions for critical control points and critical limits that have questionable results. This operation is undeniably an integral part of your HACCP plan.

At FoodDocs, we have made sure that thermometer calibration is a covered and well-emphasized part of our digital food safety management system with built-in digital HACCP plan software. Our digital HACCP plan covers thermometer calibration as a preventive and corrective measure for operations that involve temperature reading. In addition, our digital FSMS product can automatically create a digital monitoring form for recording thermometer calibration for continuous compliance. 

Calibration log in FoodDocs

Calibration log in FoodDocs


This program helps any type of food business get a comprehensive digital HACCP plan that is specifically built for their operations in just an average of 1 hour. By answering a few questions related to the nature of your operations, our system powered by artificial intelligence automatically generates a digital HACCP plan built based on your provided information.


food safety plan builder


This HACCP plan can be further customized to accommodate more specific information. With this feature, you can further tailor your digital HACCP plan to fit your food business more perfectly. Save up to 120 hours when you choose to build your HACCP plan with us rather than hiring a food safety expert to build a HACCP plan for you. In addition, our built-in HACCP plan builder considers the most relevant and updated food safety laws related to your operations.


Our system can help you create a comprehensive HACCP plan for your food business with the following major contents: 

  • A basic flow diagram representing your food operations.
  • Properly identified and analyzed food safety hazards based on your food business.
  • Appropriate critical control points and critical limits.
  • Corrective actions suggestion for critical limit breaches.
  • Sets of proper monitoring procedures with detailed instructions and digital monitoring forms for each operation.


You can get all of this awesome HACCP plan by simply signing up with us. Our system can even allow you to print out your HACCP plan for an audit with a more traditional approach. Alternatively, you can simply share your digital HACCP plan with an inspector and present everything online. Our digital HACCP plan builder can help you get food safety compliant as fast as possible.


Continue your food safety compliance by implementing our digital FSMS for your daily monitoring tasks. With our system, you can get the following benefits:

  • Automatically generated monitoring forms based on your daily operations. These monitoring forms can be set to be prefilled by our system based on your previous data entries. You can save your employees' time with this feature.
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  • Access all your digital documents from single cloud storage and save up physical space.

Our team of food safety experts aims to make food safety and compliance with food laws and regulations accessible to every business. With this digital FSMS with a built-in digital HACCP plan maker, food businesses can easily achieve compliance when compared with the traditional process. Get your own digital HACCP plan in an average of 1 hour and discover the software during our free, 14-day trial.



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