Foreign material control, especially metal contamination, has become an integral element of food quality and safety programs. But, no matter what processors do to ensure the foods they manufacture are free from metal and other foreign materials, there are instances when something gets into that final package.

Metal detectors and X-ray machines do not detect all metals, only metal or other materials down to a certain size. The sensitivity of the metal detector or X-ray machine depends on its design and the type of product being tested.

With metal detectors, the smaller the aperture, the greater the sensitivity. However, their sensitivity is less when testing frozen foods or large packages. Consequently, any operation considering metal detector technology should work closely with the equipment manufacturer, not only to set up the equipment and teach staff how to operate and maintain it, but to establish the proper test standards and obtain a letter defining minimum sensitivities.

X-ray equipment can detect objects as small as 0.5mm and eliminate metal, glass (silicates), hard plastic, bone and stones. It also can determine mass analysis, confirm fill levels and seal integrity (crooked or missing caps) and recognize missing product. But, since the equipment operates on density differentials, it may not be the best option for some products like breakfast bars that may contain ingredients such as various nuts, seeds and grains.

Facilities that process foods in foil packages may want to utilize a metal detector prior to packaging or an X-ray machine on the final package. Processors that manufacture boil-in-bag products should look into X-ray technology.

Many processors struggle with how X-ray equipment and metal detectors should be used in their food quality and safety operations. Should they be a critical control point or preventive control or a quality control point? The 4th edition of the FDA Fish and Fishery Products and Hazards Guidance indicates fish and fishery product processors with metal detectors should treat them as a critical control point. If FDA uses this document when developing guidance for FSMA, metal detectors will be deemed to be a critical control point or preventive control in other types of food processes.

The preventive controls regulation does not mandate validation studies to ensure processors’ systems will effectively control potential hazards. However, during an audit, processors must clearly demonstrate their equipment can detect test standards at all times and under all conditions. Plus, the validation studies for the equipment must be documented.

X-ray technology provides greater flexibility when it comes to foreign material detection, yet the machines can be more expensive. They also require greater care during operation; the units must be shielded, and the shields must remain in place. In addition, workers must be properly educated on X-ray hazards, and the training must be documented.

Client requirements are also a consideration when deciding whether to use metal detectors or X-ray technology. For instance, Costco requires suppliers to use a foreign material detection device to control potential physical hazards unless the risk in the facility is deemed to be low. If an auditor determines the risk level is medium to high, the facility must install a foreign material detection device, preferably X-ray. In fact, Costco encourages all suppliers to consider an X-ray device when they add or replace equipment for foreign material detection.

The proper inspection equipment for your facility depends on a variety of needs, risks and regulations. But, there is one thing you should always remember: These devices can never replace good maintenance procedures, proper good manufacturing practices, well-written and executed standard operating procedures, and the proper operation of your equipment.


Metal Inclusion: Chapter 20; FDA Fish and Fishery Products and Hazards Guidance, 4th edition, USFDA, 2015,

“Current Good Manufacturing Practice Hazard Analysis and Risk-Based Preventive Controls for Human Food, 21 CFR Part 117,” USFDA, Government Printing Office, 2015.