Safety and hygiene are always top of mind for food processors. Not only is there an important need to avoid bacteria like salmonella and listeria, but food processors also face a risk from foreign object contamination. Objects like stones can be accidentally mixed in with natural food ingredients during harvesting, and foreign objects such as plastic can be inadvertently added to a processing line at the manufacturing facility. So how do you screen your production line to minimise the risk of foreign object contamination? There are two kinds of modern detection systems: x-ray inspection systems and metal detectors.


X-ray inspection systems

X-ray systems in the food processing industry rely on a computer system to detect foreign objects (rather than a worker manually viewing a screen). The x-ray machine passes a beam through a product and then relays it back to a computer system, creating an image. The computer decides whether the product should be accepted or rejected based on visual analysis of the image.


One of the main advantages of an x-ray inspection system is it can detect many materials that metal detectors cannot – things like glass, rock, bone, plastic, and rubber.  X-ray systems are also capable of screening products with metal-based packaging such as foil, metallic film or aluminium.  Metal-based packaging is incompatible with a metal detector, so if your products involve any metallic materials, an x-ray inspection system may be a better option for your processing line.


The most difficult job of an x-ray inspection system is distinguishing a contaminant from the product or packaging. For an x-ray inspection system to work correctly, the contaminant needs to have enough contrast to the product, so that it can be detected in a greyscale image. This contrast is determined by a material’s density, so objects with low density such as hair, paper or fabric, are harder for x-ray systems to find. False positive readings can be costly, so it’s wise to run an extensive test of your products to determine whether an x-ray system will be able to detect contaminants in your products.


X-ray inspection systems have a few other disadvantages. They are slower than metal detectors, as they need a constant, reliable speed to work correctly. X-ray systems will also wear out, and they need regular maintenance at least once a year from a technician.


Metal detection systems

Metal detection systems work by transmitting an electromagnetic field between opposing coils. If a metallic object passes through the detector, it will disrupt the electromagnetic field, signaling that metal is present. Modern metal detectors can detect objects at just 0.5mm thick, and they are able to detect a contaminant regardless of its density or consistency of shape, unlike x-ray inspection systems.


Metal detector systems are cheaper and last longer than x-ray systems, and they can be used anywhere in the processing line, making them a versatile screening method. Metal detectors can detect all metal contaminants, even lighter ones such as aluminium. However, because metal detectors can only detect magnetic or electrically conductive objects, other contaminants such as glass are invisible.


One of the main challenges in using a metal detector is the risk of creating false positives. Wet or moist foods may be conductive, creating an interference signal, which affects the metal detector’s ability to screen correctly. The presence of certain ingredients like salt, acid and fat can also create false positives if the metal detector has not been calibrated correctly. Packaging presents another challenge – if you use foil or other metal-based packaging, you won’t be able to run these products through a metal detector.


Which should you choose?

The choice between an x-ray inspection system and a metal detector depends on your budget and what type of contaminant poses the biggest risk in your processing line. If you are concerned about metal contaminants, then a metal detector may be more suitable for you. If you’re more concerned about non-metals, an x-ray machine might be the better choice. If you’re concerned about all kinds of contaminants, and your budget allows it, consider installing both machines.


AccuPak is one of Australia’s largest manufacturers of packing, filling, bagging and palletising machinery and equipment. We distribute the Fortress brand of food metal detection systems and the latest available x-ray technology, and the experienced AccuPak team is committed to providing excellent after-sales support. To discuss which product inspection system is right for your food processing business, contact us today.