Management January 24, 2019 Last updated January 21st, 2019 3,333 Reads share

Food Metal Detection Testing Procedures

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In the era of Big Data, companies aren’t the only ones looking for access to information. Today’s average consumer has become increasingly vocal in their demands for transparency when it comes to food safety and regulation. Governments around the world have responded to this need for safety with an increase in food metal detection technology. Now, companies must be able to provide regular proof on demand that they are complying to new safety regulations, and that may include ensuring production lines have the equipment to detect unsafe materials before packaging. We’re in luck that basic food safety procedures, such as testing products for metal contaminants, have evolved in impressive ways since the first industrial metal detectors rolled out in the United Kingdom in 1948.

Metal detection testing procedures

Education is key to a successful metal detection test. It is imperative that testing procedures be documented and properly presented to anybody involved in the process, from maintenance workers to technicians. Documentation should be easily accessed by workers who should be able to consult it at any time. Anybody who has not been properly educated in testing procedures and proper equipment operation techniques should not be given access to things like sensitivity adjustment controls. In fact, such important features should be password-protected from the get-go from employees who have not been educated in handling such aspects of the testing process.


Conventional systems

Different products, clients and equipment call for different types of tests. Conventional food grade metal detectors like ‘balanced coil’ systems or ‘ferrous-in-foil’ systems need to be tested using different test packs. These packs should be made using products that contain no traces of metal and must be clearly labeled as test packs so that they are not accidentally distributed with normal products. They should then be appropriately ‘contaminated’ in order to test the detectors’ abilities when it comes to identifying ferrous, non-ferrous and stainless steel contaminants. Each of these three packs should be marked so that workers can quickly and clearly identify where the contaminants have been placed.


Send each test pack one after another through the detector, using normal spacing and line speed configurations as you would in a real production setting. This is called a consecutive test. You should also conduct a memory test, in which each test pack is sent through the detector followed by a pre-tested standard pack that is contaminant-free. In this situation, the goal is to ensure that the appropriate packages are rejected (i.e. the test packs) and separated from contaminant-free products (i.e. the standard packs).


In the event that a standard pack is also rejected along with the purposely contaminated test pack, the system will need to be stopped in order to figure out why a ‘blanket rejection’ occurred. This may have to do with the timing or the spacing, or any number of other factors. You may have to ask yourself ‘why’ several times before you find the root cause of an issue. If blanket rejections continue to occur throughout testing, the best thing to do is to contact the equipment manufacturer for consultation.


Gravity and pipeline systems

Conventional metal detectors for food industry use come in different configurations for different types of products. Gravity and pipeline configurations need to be tested during production to be properly observed. Preferably, incorporate test pieces into the regular product flow, using appropriate sizes for optimal sensitivity testing. It is also possible to place the test pieces between the pipe and the metal detection head. In both cases, observe that the rejection system is operating properly. Keep in mind that you will not be able to test the timing with this type of testing.

When to test

Equipment testing procedures will vary depending on the particular product and client needs. In general, however, it is advisable to have testing scheduled at the start of any shift or between product changes. Testing should also occur on an hourly basis at the very least – often enough, really, so that should something goes wrong, the number of affected products is kept relatively low.  


Potentially contaminated products must be recalled and rescreened, going back to the time of the last successful test. If faulty testing equipment is at play, use another functioning metal detector set to the same standards, such as an offline portable quality assurance metal detector. Keep in mind that for packages wrapped in foil, it is preferable to be able to at least test the product before it is wrapped. If you are limited to testing the product after it has been foil-wrapped, a ferrous-in-foil detector must be used – but these only pick up on ferrous metal contaminants.


Rejected products

It is important to educate staff in dealing with rejected products in an appropriate manner. There should be a scheduled inspection in place regarding rejected products, as they need to be investigated within the hour (sooner, if products are frozen). If frozen products have thawed out, they will need to be refrozen to be properly investigated.


Use the same industrial metal detectors once regular production has come to an end, in order to re-screen any rejected packs. If production cannot be stopped, use another working detector that shares the same sensitivity configurations or higher. You will want to repeat the exact same test, positioning products in the same way. Do this two more times, for a total of three re-screenings per rejected pack.


If a product continues to be rejected, it is extremely important to discover what the contaminants are and when and where they came from. On the other hand, if contaminant-free products are being rejected, the metal detecting equipment will need to be inspected with consultation from the equipment manufacturer. In either case, customers must be kept in the loop in writing so that they are aware of any problems in the manufacturing process.  



Companies must keep thorough documentation and records in relation to many aspects of the food production process. This is not only important to prove to inspectors that they are complying to safety regulations, but also to facilitate recalls and to identify contaminant sources.

Keep records on the following:

  • New equipment purchases.
  • Movement and relocation of equipment, old or new.
  • Test results (time, sensitivity, number of rejected packs, number of contaminants, types of contaminants, actions taken if any, etc.).
  • Preventative maintenance plans.
  • Communications with customers providing incident reports.
  • Personnel training.



Industrial metal detectors are only useful if trained workers are able to take appropriate measures to respond to incidents in a timely, appropriate manner. Take care to ensure that every employee involved in the production process knows how to identify contaminant sources or other potential problems. With good documentation, regular testing/maintenance procedures in place, and proper staff training, any company should be able to proudly declare that they adhere to strict safety protocols, ensuring the quality of their products and the integrity of their name.

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Steffen Ploeger

Steffen Ploeger

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