How to meet retailers’ metal detection testing requirements

How to meet retailers’ metal detection testing requirements
Photo - Mettler Toledo

Testing of metal detection equipment is often a key aspect of the codes of practice which retailers expect their suppliers to adhere to. What are the tests that food manufacturers must undertake to comply?

Pressures on food retailers come from many different directions: imposed on them from government or industry; expected of them by consumers, whose health and safety are in their hands; and, in a sense, from within too, in the shape of moral and social responsibility standpoints.

To disregard the needs of any of these stakeholders in respect of the sale of safe, high quality food products is to invite the risk of severe and potentially long-lasting reputational damage. For this reason, over time, retailers have each developed codes of practice that they expect all their suppliers to demonstrate adherence to. For food manufacturers, that means mandatory food safety management procedures, implemented at critical control points in production and packing, as identified by established hazard analysis audits.

Very often, this also involves the use of metal detection to help detect certain types of contaminants that may be found in food products. One part of the retailer code of practice is very likely to specify the expectations the retailer has of its supplier in respect of frequent and appropriate testing of the metal detector to verify that the system and associated components such as reject systems, beacons and fail-safes continue to perform to the necessary standard.

Food companies operating metal detection systems must understand the testing requirements of the retailers with which they are doing business. They should be able to undertake the required levels of system testing plus prove that testing regimes meet the specified standards.

What, therefore, are the tests that retailers require? With metal detection, there are three main tests, plus a fourth type of test that some retailers may also mandate. The three main types of metal detector test are:

o The Standard Test

o The Consecutive Test; and

o The Memory Test

Each of these tests is carried out using ferrous, non-ferrous and stainless steel test packs. For reasons of standardisation and consistency, best practice is to always put the different test packs through in exactly that sequence listed. In addition, the ferrous test piece should be positioned at the front of the ferrous test pack, the non-ferrous test piece in the middle of the non-ferrous pack, and the stainless steel test piece positioned at the rear of its pack. To test the metal detection system’s capabilities, its sensitivity and its reject timer settings, test pieces should also be positioned to pass through the geometric centre of the detector’s aperture.

In the Standard Test, metal detector operators insert the three test packs in sequence into the middle of normal operation of the system, with random numbers of clean packs between them, but with correct spacing maintained between packs (both clean and test). Only the test packs should be rejected in a successful test.

Where retailers require that the reject mechanism of the detection system can cope with multiple contaminated products in succession, the Consecutive Test becomes appropriate. In this test, the operator introduces the test packs in the correct sequence one after the other, with normal pack spacing and at normal production speed, but without clean packs in between. In a successful test, the metal detector will reject all three test packs.

The Memory Test is an enhanced version of this and is preferred by some retailers. This introduces a clean pack between the test packs, which are again inserted in the ferrous/non-ferrous/stainless steel sequence. All packs should be correctly spaced. If successful, the test will see the three test packs rejected, and the two clean packs in between passed as good products.

Large Metal Test

The fourth type of test is called upon where companies are using metal detection equipment with a photogate side reject device, such as a pusher or air blast. Retailers often want to check that the reject timers on these systems are correctly set up. If they are not set up correctly, then contaminated packs might be missed by the reject system. Known as the “Large Metal Test”, this test requires the operator to place a large metal sample (often a 20-millimetre diameter ferrous ball) into the test pack. If the photogate timer is correctly set up, the reject mechanism will successfully divert the test pack into the reject bin. If it is not correctly set up, the mechanism may act too early or too late, and miss the contaminated pack.

Photo - Mettler Toledo


Carrying out the tests is only one part of meeting retailers’ requirements; food manufacturers must also be able to prove to retailers and/or auditors that they are doing so. This is where the increasing sophistication of metal detection and other product inspection systems comes to the fore. It has been the practice – and still is in many places – for testing records to be kept on paper. There are obvious drawbacks to this, including risks of paper records being damaged or lost, and susceptibility to manipulation.

However, the increasing use of digital metal detector systems, alongside ProdX™ data management software by Mettler-Toledo, means that users can benefit from automatic prompting of compliant testing within prescribed intervals, electronic storage of test results, and smart optimisation of production and line operation. Such enhanced capabilities are already leading to greater expectations from retailers in terms of how testing compliance is reported, and this will increasingly be reflected in their codes of practice.

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