What Lies Beneath
By Megan Pellegrini

As meat- and poultry-processing plants become more stringent on food-safety standards, how is metal-detection technology keeping pace?
Food recalls due to microbiological contamination certainly receive plenty of media attention. But one never hears of meat and poultry products being recalled due to physical contamination by metal or glass. Processors have metal detector and X-ray machines to thank for that. How has detection technology changed since it was introduced in the late 1980s to best serve processors?
In short, not that much. The machines introduced in the 1980s and 1990s already were pretty sophisticated. Changes to the machines since then have largely been to fine-tune the production process, because processors operate in a tremendously different environment today.
Meat- and poultry-processing plants are becoming more stringent on food-safety standards, period. These changes include demanding better technology to pinpoint metals and installing updated programs for record keeping. Their customers expect them to provide proof of detection and removal of a minimum level of metal contaminants. All of these higher standards, of course, also lead to better product quality in the end.
Metal detectors are well-established in the meat and poultry industries. X-rays, electrical conductivity, magnetism, laser reflectance, color, gravity and terminal velocity also are used by processors for detection — mainly as backup after product runs through metal detectors. Line strainers are commonly used to remove foreign objects from liquid products. And magnets are well-suited for removing ferrous materials from particles and pumpable liquids, says Tim Bowser, Ph.D., food processing engineer with Oklahoma State University’s Department of Biosystems and Agricultural Engineering.
“You almost never hear about bones or metal in products,” says Scott Russell, Ph.D., associate professor of poultry processing and products microbiology, University of Georgia. “The data for these companies is pretty staggering. Physical hazards are not a reported problem anymore. They are well taken care [of] in the plants.”
However, traditional metal detectors and X-ray scanners do have limitations and customers need to be aware of that, says J. Craig Wyvill, head of the Atlanta-based Georgia Tech Research Institute’s Food Technology Processing Division and director of the Agricultural Technology Research Program.
For one, they cannot detect every particle of metal that goes through them. Wyvill notes that metal detectors can detect foreign objects better in frozen, not fresh product. Also, he points out that X-ray systems still need better signal processing and imaging devices.
The level of moisture, packing material, vibrations and electrical interference can interfere with the sensitivity of the detection machine, says Skip Steward, Ph.D., vice president of regulatory affairs for the American Meat Institute (AMI). Also the electrical conductivity in fresh meat can generate a signal even when metal is not present, known as the “product effect.”
Recently, the Georgia Tech Research Institute was asked by major metal-detector manufacturers to look into comparison testing of metal detectors. The manufacturers wanted to improve their product and make sure their performance met with customer expectations. According to Wyvill, they said customers didn’t fully understand the technological limitations of metal detectors.
“Customers can’t expect more than the metal detector sensors and X-rays can provide,” says Wyvill. “They need to use them knowing they are not perfect. Speed and the product itself can interfere with detection methods.”
The ABCs of metal detection
Metal detectors generally can detect anything from metal wires to lead-shot that have found their way into the meat supply, says Steward. In fact, they are capable of detecting medium to larger size ferrous, some non-ferrous and magnetic steel foreign material in fresh and frozen, wrapped and non-wrapped packages.
Metal detectors can be used in various production phases, such as during finished and bulk ingredient and product inspection. And it’s not a bad idea to position them after production equipment that may be known for breaking or chipping metal materials.
Industry analysts advise setting metal detectors at their maximum acceptable sensitivity setting, which will allow them to perform reliably without excessive product rejections. If a machine detects metal in a product, it then diverts it off the production line for manual inspection. The main criterion used to set the machine’s sensitivity standard is the size of the metal particles. Generally, spherical, non-magnetic particles larger than two millimeters and all spherical, magnetic particles larger than 1.5 millimeters are removed.
Glass, however, can be difficult for metal detectors to locate. So, it is usually not even allowed in manufacturing environments.
“We don’t hear about glass contamination at any frequency in meat and poultry products,” says Steward.
At only a decade old, X-ray machines are a relative newcomer to the meat and poultry industry. Current X-ray systems are able to detect ferrous, non-ferrous and stainless-steel contaminants, and a wide range of non-metallic contaminants such as stone, calcified bone, glass and some very dense plastics. Many X-ray detectors also can find defects, missing or misshapen parts and check the weight of food in individual compartments of a multi-compartment package.
In addition, they can detect metallic contaminants within packaging such as aluminum trays or metallic films. They are also able to distinguish between legitimate metals, such as sausage clips or aluminum tins, and unwanted items.
Whats new
Although the essence of metal detectors hasn’t changed, manufacturers are making continual adjustments to address their shortcomings. Metal detectors, for example, are now much more rugged, sensitive and automated today, says Bowser. Many are even waterproof to accommodate the harsher cleaning procedures used at plants. And their price has gone down quite a bit.
In addition, most metal detectors have automatic error detection, so they are less likely to send a product offline that is really not contaminated; thereby, saving the manual labor costs of physically inspecting the suspicious product. Digital signal processing technology also has improved vastly, so detectors can run at a higher operating frequency while they still automatically adjust for changes in product density.  
Metal detectors have enhanced detector construction, which allows the machine to better detect and remove very small pieces of metal and feature a more advanced operator interface.
Multi-frequency metal detectors are giving processors the flexibility to run different products with different “product effects” through the same machine. All products have the aforementioned “product effect” or “signal” due to its moisture, salt content, temperature, ingredient composition and size, which can affect the metal detectors’ electromagnetic field. Today’s detectors are able to phase out much of this signal to restore reasonable levels of sensitivity. X-ray manufacturers are also trying to improve detection sensitivity by working with new software technology, says Wyvill.
“Clearly, work is still going on with X-ray and traditional metal detector systems to reduce errors and improve accuracy,” he says. “They still have a ways to go.”
Installing GMPs
“Both metal and X-ray detectors are very effective when designed and operated correctly,” says Robyn Nick, director of marketing for Coleman Natural Foods. She notes that Coleman uses both metal detectors and X-ray detectors for locating foreign objects. “The health and safety of our consumers and employees is paramount. At Coleman, we take even the slightest risk seriously and have adopted multiple safety protocols, risk management practices and precautions to safeguard our products.”
By using both metal and X-ray detectors, Coleman ensures its product safety against the systems’ weaknesses. Nick notes that the limitations of metal detectors are size detection sensitivity, product variability sensitivity and false positives. X-ray scans aren’t as effective when product density varies.
“Metal detection systems have improved, particularly with regard to durability, reliability and consistent performance,” says Nick. “Early X-ray systems were not as reliable and were expensive. Improvements to current X-ray systems include being able to detect metallic contaminants within packaging such as aluminum trays or metallic films, and detection of a wide range of non-metallic contaminants.”
She notes that the greatest opportunity for improvement in either metal detector or X-ray technology is always in proper rejection of contaminated product.
Johnsonville Sausages, based in Sheboygan Falls, Wis., recently switched to X-ray technology from metal detectors. During its testing period, foreign object consumer complaints decreased to and stayed at zero, sealing the deal on the switch.
However, human vision and perception remain low-cost methods that still serve as “the gold standard and the most relied upon means of detection worldwide,” notes Bowser. “For many years, ‘dilution was the solution to product pollution.’ Today’s analytical methods can pick up contaminants at very, very low levels making this old rhyming proverb nearly obsolete.”
Alice Johnson, DVM, vice president of food safety, government regulation and public affairs for Butterball LLC, points out that the best form of material detection is good preventative measures.
“By closely following the routine of the poultry or livestock, the risk of finding foreign materials in their bodies is greatly reduced,” she says. “As a second measure, very careful, by-hand inspection is the next best way to ensure a completely untouched bird.”
She also notes that process control through appropriate Good Manufacturing Practices (GMPs) will reduce the risk of foreign objects getting into the product. For example, plant owners can prohibit employees from wearing jewelry, ban glass bottles inside the plant and make sure all equipment parts are accounted for through routine equipment checks.
“Technology can always be improved upon,” she says. “The sensitivity of the equipment will improve, allowing for greater accuracy. And packing itself can be improved to prevent the risk of pieces falling off or getting inside the product.”
AMI’s Steward agrees that plant employees should pay proper attention to cleaning and sanitation, and inspect grinders and equipment for foreign material such as pens and clipboards. Although metal detectors are very effective today, many variables can impact their performance. Indeed, it is still crucial to validate the equipment by testing its performance, he says.
“Plants should run experiments by putting metal in their products and ensuring their machines can detect them,” says Steward. “Equipment validation is important as improvements and changes take place.”
Detecting the future
Any equipment changes for the future will need to be user friendly, as the meat and poultry industries aren’t immune to high staff turnover. Industry analysts expect to see metal detector and X-ray machines become easier to set up and operate. Simplified data-management systems will need to become standard and compliant with existing plant networks.
Future equipment will be less affected by the product effect and sensitivity capabilities will increase. In the next three to five years, meat and poultry processors can not only look for better sensitivity but more features, improved networking ability and better customer interfaces.
According to Bowser, non-contact methods of measurement and detection are still needed, as well as fewer false positives and higher throughput. In addition, “lower installed cost will never go unappreciated,” he says.
“Improvements in diagnostic imaging should focus on further developing technology that is sensitive over a wide spectrum of products of varied type and composition,” notes Alling Yancy, Ph.D., vice president of food safety and product programs for the U.S. Poultry and Egg Association. “In-line diagnostics that more effectively detect unacceptable natural, and/or foreign, materials will allow for more rapid isolation of suspect product, thereby reducing the amount of product placed on hold awaiting further action.”
He notes that new technology should not be cost-prohibitive nor have a detrimental effect on product quality, and must be user friendly and sturdy enough to withstand the rigors of the typical processing plant environment.
With plant managers watching the animals to make sure they don’t ingest metal or glass, keeping an eye on the cleanliness of their plants to make sure nothing slips into a machine and employing the latest metal detection or X-ray systems, it’s pretty difficult for a foreign object to wind up in a meat or poultry product.
“If there is foreign material in a product, which is a very infrequent event, plants will detect it,” says Steward.