Five Key Steps to Increase Food Product Safety

Robust testing practices for foreign body detection require validation, verification and routine performance monitoring

By Robert Rogers, Senior Advisor of Food Safety and Regulation of Mettler-Toledo Product Inspection

If food contaminated with foreign bodies reaches retailers or consumers, the direct and indirect costs for food manufacturers are immense: high recall costs, a damaged brand image and customer cancellations of supply contracts.

This is why it is so important to install inline product inspection systems to detect foreign bodies on the production line. However, simply installing the machines is not a silver bullet. To be truly effective, they must be backed up with robust testing practices and staff must adhere to a number of process steps over the entire lifecycle of the inspection system. Only regular testing can confirm that system performance is within the set detection sensitivity specification, and that product standards of retailers, consumers and the Global Food Safety Initiatives (GFSI) are met.

There are five key steps to increase product safety, and within these steps, the issues of validation, verification, and routine performance monitoring are intertwined.

  • Validation ensures the device meets the requirements for the detection of likely contamination risks with the specific product, and does so without exceeding the permissible false reject rate.
  • Verification through regular assessments ensures the system works as expected, with test results documented. The expertise and qualifications of line personnel to carry out local tests and monitoring can also be included.
  • Routine Performance Monitoring is a series of performance tests that are performed at short, regular intervals, confirming that the inspection system is operating according to expectations and within the defined limit values. If a critical limit value is exceeded, corrective measures are required to ensure non-compliant products are efficiently and cost-effectively removed from the production process.

With those issues in mind, here are the five steps to robust testing practices:

Step 1: Use of Correct Test Samples

The use of certified test samples and weights helps to ensure compliance with food safety standards, guidelines, and legal regulations, and guarantees that the inspection systems operate according to the correct specifications. Test samples are available in many different formats, with test cards being the most common format for dry applications, test balls or tablets suitable for applications with powdery materials, test rods recommended for free-fall metal detectors without a reject mechanism, test balls or rods for pipeline applications, and tablet-shaped test samples available specifically for X-ray inspection. For vertical metal detection applications, an Automatic Test System (ATS) is also suitable to detect metal contaminants such as ferrous, non-ferrous and stainless-steel metals.

Step 2: Use of suitable test products

The specification of suitable test products as well as the following requirements should be defined and integrated into the test procedures:

  • the process of ensuring that a product is free of foreign bodies before test samples are inserted or attached
  • the manner in which test products are prepared, including the positioning of the test sample inside or outside the test product
  • the frequency with which the test products should be created, taking into account properties such as durability and shelf life of the product
  • the procedure for marking test products to prevent them from entering the supply chain inadvertently in the event of a failed attempt

Test products outside of the food item can be used to test the fail-safe system. However, they should be similar in size, shape, and weight to the food products that are transported on the line.

There are a number of particular recommendations here that are specific to different applications. For instance, with packaged products, test samples should be placed at those points of the product that are most difficult to inspect. With metal detectors, they should be placed in the front, middle and rear section of the test products, while with X-ray inspection systems, the samples should be positioned both on and under the product.

Test tablets or test rods are usually used for bulk or loose products, and for free-fall applications with unpackaged products, the test samples should be introduced directly into the product flow. For pipeline applications, the test samples should be introduced into the production flow via a filler opening, and the product with the foreign body is then passed through.

Step 3: Compliance with recommended test procedures

Different test procedures may be required to comply with specific food safety codes of conduct. When testing for different types of foreign bodies, these tests should at least meet the following requirements:

  • relevant standard recognized by the GFSI
  • possible external customer specifications
  • rules and regulations of the retail industry
  • company-specific guidelines and test requirements

There are differences in test procedures when using either conveyorized metal detectors or conveyorized X-ray inspection systems. For metal detectors, the basic test and the preferred method is to test consecutive products, with (as a minimum) one test sample in the front, one in the middle, and one in the rear section of the test product. The metallic test sample should pass through the geometric center of the metal detector, as this is the least sensitive area. As an alternative, companies can choose to test isolated products, but this method has the drawback of not checking the reliability of the metal detection system with regard to the detection of several consecutive contaminated products.

For conveyorized X-ray systems, the tests should be carried out in the most difficult area of the product in order to push the X-ray inspection system to the limits of its detection performance. Test samples should be placed randomly to ensure that the system is able to detect contaminated products regardless of their position in the production line.

In addition to testing consecutive products, retailers may require additional performance monitoring tests to be performed. These might include the memory test and the ‘Large Metal Test’. With the memory test, three contaminated products (which should be rejected) and two non-contaminated products (which should be accepted) should pass through the metal detector. This is to confirm that the metal detection system is capable of distinguishing between ‘good product’ (no metal contaminants) and ‘bad product’ (metal contaminants present) when working at high speeds, with packs placed closely together on the line.

The large metal test serves to confirm that the photogating system on the metal detector is working properly, and it is recommended that the test is undertaken at least once a day, and ideally once a shift. In the test, a large metal test piece of 20 millimeter ferrous is introduced to the metal detection system, either on its own, or among other packs. The test is successful if the product contaminated with a large metal foreign body is detected, the test product is rejected and the production line is not blocked.

Step 4: Compliance with test intervals

GFSI recognized standards, customer and retail requirements and company guidelines regarding shelf life and product blocking times must all be considered when setting the frequency of tests. As a general rule, the test intervals must always be situated within the quarantine period time, which is the time between when a product is produced and when it leaves the production site. The performance tests at the beginning and end of daily production should be emphasized, as these serve to confirm that the detection and rejection takes place in accordance with the specified standards and that any additional warning systems are functioning properly.

It is also advisable to carry out performance tests at regular intervals during the production run and at the beginning of a new product run. The aim is that every product that has passed the inspection system, since the last successful performance test, can be retrieved while still on site if the system does not pass the test. In addition, a performance test should be carried out with every batch change – especially if there are changes to the product type, or changes have been made to the product and/or system settings. A performance test is also required after repair-related downtimes, to ensure that the product inspection system and the reject mechanism are still operating according to the established standards.

Step 5: Electronic data management

The trend to automate data collection processes is rapidly accelerating. There are benefits in terms of time saved in the documentation and recording process, as well as a reduction in human error endemic to any manual data capture process.

A secure and up-to-date data solution actively supports food safety regulation compliance and helps prove due diligence. In addition, in the event of a product recall, all product quality data can be easily retrieved. Real-time documentation of all inspection test results, and machine parameter changes also allows production issues to be quickly identified and resolved.

The proven method to automate data collection processes is to directly connect data management software to the inspection device. This facilitates communication between multiple product inspection technologies, and connects to a manufacturer’s enterprise resource planning (ERP) or manufacturing execution system (MES).

Good testing guidelines and training ensure food safety

There are many considerations to make, and many procedures that must be followed, if food manufacturers are to detect foreign bodies on the production line and reduce the risks of product recall. The keys are to establish good testing guidelines at the start; to ensure that staff understand what is required and are able to perform suitable tests; and to maintain accurate, easily accessible records of testing activity. Product inspection technology of course plays a critical role, but it must be backed up by good operational practice which is demonstrated through robust and regular testing.

About the Author

Robert Rogers is the senior advisor for food safety and regulation at Mettler-Toledo product inspection. For more information, visit

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