Op Ed: Blind Spots in Food Metal Detection

Double the Rejection Detection

The rejection of one piece of metal is fairly easy to assure with a good standard operating procedure. However, what happens when there are two rejections simultaneously on the line? If you have the proper type of reject mechanism and the timing is set up correctly, you should be good. However, picture a plunger-type reject mechanism, which is pneumatic. If the plunger pushes to remove one product by the time it retracts and pushes again, it may not be able to reject the next product depending on the type of product and set up of the machine. Many companies are now running test spheres at the leading and trailing ends of the product and they are running multiple samples in a row with their test spheres to assure that multiple contaminates will reject.

Train People on Handling Rejected Product

When product is rejected, make sure only trained people can access the rejected product. Employees with good intentions may put product back on the line if they see it sitting in an open rejection bin. That is why products should be rejected into a locked reject bin so only qualified employees with a key have access. The employees with access to the rejected product should be trained on how to evaluate the rejected product for foreign material and how to properly dispose of it. Many progressive companies are now taking the stance that any product that rejects from the metal detector is to be disposed of even if it is run back through the metal detector five additional times with no reject. They still evaluate the product to determine the source of contamination when possible, but no rejected product goes back on the line. All the proper controls must be in place to prevent false-rejects or you will spend your days evaluating and throwing out rejected products.

Placement of Metal Detector

The placement of the metal detector is just as essential as it functioning properly when it comes to metal detection. The best practice from a HACCP standpoint is to place the metal detector in the last position in the process to prevent a possible hazard. For instance, if you package bulk product into bags or bulk cases, it is best to have the product metal detected in the finished package if at all possible. If the product is metal detected before it is packaged then you take a risk that there could be an occurrence of metal happening after the metal detector and before it is packaged. Contamination of finished product can occur after the metal detection if “metal detectable” belting breaks and ends up into a bulk case or tote with what was considered good product. This can be prevented by implementing metal detection after the product is packaged. Some companies have two metal detectors in line at different locations. One metal detector is located up front in the process where it is able to detect to a more sensitive level before it is packaged and then one metal detector placed after it is packaged where it may not be able to be as sensitive.

Don’t forget, a metal detector’s sensitivity and capability can be affected by the size of the product being detected. For instance, if running a 4-ounce package of product through a 4-inch metal detector aperture, you are generally going to pick up much smaller pieces of metal contamination than if you run a 30-pound case with multiple packages through a larger aperture metal detector. Therefore, you have to decide the best place in the line to place a metal detector or detectors to eliminate the hazard. If you have any questions on the best placement, speak to others in the industry or reach out to a metal detector supplier for advice.