The American Society for Quality defines calibration as follows: "The comparison of a measurement instrument or system of unverified accuracy to a measurement instrument or system of known accuracy to detect any variation from the required performance specification."¹

Calibration is really a verification activity. Processors are ensuring that the instruments they use to ensure food safety, food quality, and legal issues are functioning and accurate. A range of instruments require calibration, including but not limited to: temperature monitoring devices, pH meters, pressure gages, water activity meters, belt speeds, product flowmeters, metal detectors, and refractometers. Failure to properly maintain and manage your monitoring instruments can result in serious problems including product recalls, foodborne illness, or injury.

In 2007, a botulism outbreak was attributed to chili sauce produced by Castleberry's.^2,3,4 In the investigation, it was discovered that a temperature indicating device was reading high. Such a scenario can adversely affect the overall lethality of a thermal process. 

When I teach HACCP, the example I like to use that shows the importance of a well-designed and well-maintained calibration program involves acidified bell peppers in California. During the season, the company produced red, green, yellow, and orange peppers using different cuts (sliced and diced, for example) and packed them in can sizes ranging from 1 lb. to institutional (603 × 700 size cans). Over the course of the season, the company produced hundreds of lots, all of which were determined to be at pH of 4.6 or below. Toward the end of the season, a regulator visited the facility to run tests on finished product and found that several lots exceeded the pH 4.6 limit. The regulator reviewed the company records and found that, although the pH values were recorded as being adequate, there were no records showing that the pH meters had been calibrated. The company swore that it calibrated its meters regularly, but no record of this work existed. In other words, "If it is not written down, it never happened." The Food and Drug Administration (FDA) embargoed the entire season's pack and asked the company to create a sampling plan to clear the lot. The plan that was accepted would have entailed a great deal of testing and expense. The company decided to destroy the entire lot—all because it neglected to record calibration data. 

Purpose of a Calibration Program

The goal of a calibration program is to ensure that all instruments used to monitor food safety, quality, and issues related to regulatory compliance have been properly calibrated and are operating effectively. The first step in the process is to conduct an inventory of all instruments and equipment used for food monitoring. This may include, but need not be limited to: temperature measuring devices, temperature indicating devices, pressure gauges, meters (e.g., pH meter, refractometer), flowmeters, scales and load cells, metal detectors, standards, magnets, and laboratory testing devices. Each of these instruments should be placed into a Master Calibration Schedule (Figure 1). 

The Master Calibration Schedule serves as an easy reference for the calibration program. The header "SQL" refers to whether the instrument is being used for food safety, food quality, or legal issues. Third-party auditors appreciate having this schedule on hand, as it summarizes the entire calibration program.

Figure 1. Example of a Master Calibration Schedule

Ideally, the company should conduct a risk assessment on all of the instruments requiring calibration and determine which are most critical for ensuring food safety and quality. This risk assessment should be carried out by the food safety team. These instruments will receive the highest priority when it comes to establishing calibration schedules. The food safety team may determine that instruments used for high-risk measurements, such as critical control points (CCPs), be calibrated more frequently.

Other Documentation Needed for Calibration Programs

Documented work instructions must be provided for calibrating each instrument. This step must include steps to verify the efficacy of the protocols. Work instructions for calibration must include the following elements:

1. Date of calibration
2. Procedures for calibration
3. Location of equipment
4. Standards used (in-house standards must be calibrated on a regular schedule)
5. Tolerances
6. Frequency of calibration (frequencies may be determined based on risk assessments, experience, or through supplier recommendations)
7. Responsible persons or group
8. Record-keeping procedures
9. Corrective actions that address the instrument and any product that may have been affected by an out-of-calibration instrument
10. Record review.

Any person assigned to conduct calibrations in-house must be trained, and that training must be documented. If the training is provided by a third-party organization (a metrics company, for example), then the company should be selected and approved according to the company's vendor quality program. 

The company must also maintain accurate and updated calibration logs that include records showing that each instrument has been calibrated and that the proper procedures were employed.

Many companies elect to place calibration tags that are water- and oil-resistant onto all instruments or equipment each time they are calibrated. Such tags must include the instrument number, the date it was calibrated, and the date of the next scheduled calibration.

It is also a good idea for management to review calibration records for instruments used for monitoring food safety each week. Calibration records will be signed/initialed and dated by the reviewer. If the pepper processor in my HACCP example had done this, it would have saved the company's whole season.

Auditing a Calibration Program

The calibration program should be audited on a regular basis to ensure that it is operating effectively. Included in this audit are all elements making up the program and the individual work instructions. This is equivalent to the internal audits described in the ISO 22000 standard, "Food Safety Management Systems—Requirements for Any Organization in the Food Chain."⁵

Senior management should review the internal audit of the program to ensure that it is operating effectively and to initiate any needed improvements. Remember, every element making up the food safety program should be subject to continual improvement.

In conclusion, proper calibration of all instruments used for monitoring food safety, food quality, and legal issues is essential for protecting consumers and the company's reputation. It is up to the company to develop, document, implement, and maintain a calibration program that achieves this objective. We do not want to see a repeat of the pepper processor.

References

1. American Society for Quality. "Quality Glossary: Calibration." https://asq.org/quality-resources/quality-glossary#:~:text=Calibration%3A%20The%20comparison%20of%20a,from%20the%20required%20performance%20specification.
2. Falkenstein, Drew. "The 2007 Castleberry Farms Botulism Outbreak." Food Poison Journal. February 25, 2015. https://www.foodpoisonjournal.com/foodborne-illness-outbreaks/the-2007-castleberry-farms-botulism-outbreak/.
3. Centers for Disease Control and Prevention (CDC). "Botulism Associated with Commercially Canned Chili Sauce—Texas and Indiana, July 2007." Morbidity and Mortality Weekly Report. July 30, 2007. https://www.cdc.gov/mmwr/preview/mmwrhtml/mm56d730a1.htm. 
4. Stier, Richard F. "The Basics of Temperature Monitoring and Importance of Ensuring Accuracy." Food Safety Magazine. October 29, 2024. https://www.food-safety.com/articles/9863-the-basics-of-temperature-monitoring-and-importance-of-ensuring-accuracy. 
5. International Organization for Standardization (ISO). "ISO 22000:2018: Food Safety Management Systems—Requirements for Any Organization in the Food Chain." Edition 2. 2018. https://www.iso.org/standard/65464.html. 

Author

Richard F. Stier, M.S. is a consulting food scientist who has helped food processors develop safety, quality and sanitation programs. He believes in emphasizing the importance of how these programs can help companies increase profits. Stier holds degrees in food science from Rutgers University and the University of California at Davis. He is also a member of the Editorial Advisory Board of Food Safety Magazine.