Technology January 22, 2019 Last updated January 20th, 2019 3,988 Reads share

Metal Detection Testing Procedures

Image Credit: Depositphotos

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 by updating food safety policies. Now, companies must be able to provide regular proof on demand that they are complying to new safety regulation. This may include ensuring that production lines have the equipment to detect unsafe materials before packaging. Luckily, basic food safety procedures, such as testing products for metal contaminants (metal detection), 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. This means including everybody from maintenance workers to technicians. Workers should be able to easily access important documentation at any time. Restrict access to things like sensitivity adjustment controls to those who have the appropriate training in such matters. In fact, important features should be password-protected from employees lacking the right training.


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 meta. Label them clearly as test packs, so that they are not accidentally distributed with normal products. They should then be appropriately ‘contaminated’ in order to test a detector’s ability to identify ferrous, non-ferrous and stainless steel contaminants. Mark each test pack so that workers can quickly and clearly identify where the contaminants have been placed.


Send each test pack through the detector one at a time, using normal spacing and line speed configurations as in a real production setting. This is called a consecutive test. It is also important to conduct a memory test. This involves sending a test pack through the detector, followed by a pre-tested standard pack that is contaminant-free. 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).


If a standard pack is also rejected along with the purposely contaminated test pack, the system needs to be stopped in order to figure out why a ‘blanket rejection’ occurred. It may have to do with the timing or the spacing, or any number of other factors. Testers may have to ask themselves ‘why’ several times before discovering 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 it is not possible to test the timing in this case.


When to test

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


Recall and rescreen any potentially contaminated products, 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. For products that are to be wrapped in foil, test the product before it is wrapped if possible. Otherwise, a ferrous-in-foil detector must be used in order to test for ferrous contaminants in foil-wrapped products.


Rejected products

It is important to educate staff in dealing with rejected products in an appropriate manner. Inspect rejected products within the hour (sooner, if products are frozen). If frozen products have thawed out, refreeze them in order to conduct the investigation.


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. Repeat the exact same test, positioning products 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. If contaminant-free products are being rejected, inspect the metal detection/equipment with consultation from the equipment manufacturer. In either case, keep customers 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 proves to inspectors that they are complying to safety regulations, and also facilitates recalls by making it easier to identify contamination 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 manner. Every employee directly involved in the production process needs to know 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.

 modern loft office stock image

Steffen Ploeger

Steffen Ploeger

Read Full Bio