Foreign body contamination in pet food or pet treats can have far-reaching effects. Metal detection and x-ray systems are most often employed at the end of production to inspect finished, packaged product, but the additional use of this technology further upstream protects more than product safety. Catching metal and other foreign objects early can protect expensive processing equipment from damage and eliminate an item before it’s fragmented into smaller parts that are more difficult to detect and remove. Inline detection upstream can also identify contaminants before more processing resources have increased the value of the product.

“If you catch a metal contaminant in its largest form at the start of the processing line, you are eliminating it at the cheapest part of the process,” explains Steve Gidman, president of Fortress Technology, Toronto, Canada. “Pushing the inspection solely to the end of the line, any contamination will be caught at the most expensive part of the production process where an entire batch of product could potentially be contaminated with unidentifiable metal fragments. At this point, the cost to a business and brand reputation could be considerably higher.” Upstream detection complements the end-of-line systems by rejecting the metal and often smaller quantities of product before it’s fully packaged.

Large-bag inspection systems for fully packaged products are commonly used for dry, kibble applications. Upstream, pipeline metal detectors work best for processed liquids, pastes and meat slurries, and x-ray systems can inspect metalized packaging and detect non-metal contaminants such as glass or bone.

Needle in a haystack

Metal detectors create a balanced electrical field and look for a very subtle change in that field. “The challenge is pet food and treat products can often be conductive as they contain added vitamins, minerals and colorants with oxides,” explains Ray Spurgeon, product manager, Eriez Magnetics, Erie, Pennsylvania “In sufficient levels, these ingredients create conductivity and what is called a ‘product effect,’ making foreign metal objects more difficult to detect.” This is also the case with wet products because moisture equals conductivity.

Packaging materials common in pet food and treat processing also challenge inline detection technology. “We are seeing an increase in metalized film packaging,” says Robert Rogers, senior advisor for food safety and regulation, Mettler-Toledo, Lutz, Florida. “X-ray inspection systems can be used for these types of packages as well as for metal cans.”

“Testing should take place regularly — usually at the start and end of each production day — then hourly and between each product changeover,” recommends Steve Gidman, president of Fortress Technology, Toronto, Canada.

The vast majority of inline detection applications in pet food involve post packaging inspections. “Package styles are diverse, and many of our products are aligned to the packaging formats that the products are offered to the market in,” says Kyle Thomas, strategic business unit manager for Eagle Product Inspection, Lutz, Florida. “Our customers are not just looking for contaminates or foreign objects that pose product safety risks. Our systems can find and verify that specific items are indeed in the package.”

Many products are packaged in case-ready packaging, which means the case acts as the store display. X-ray inspection systems detect the position of pouches inside a case and verify the case contains the correct number of pouches. Often in pouch applications, x-ray systems verify that each pouch includes a resealable closure. For canned products, x-ray systems check for fill level, product voids and that cans are properly sealed.

As inline inspection and detection requirements get more complex, equipment manufacturers develop their own unique technologies to solve these challenges.

Reading the signals

Eagle Product Inspection applies dual energy to address complexities. “Dual energy allows us to look at a high energy spectrum image and a low energy spectrum image,” Thomas says. “The system looks at both values and fundamentally classifies those values as organic and inorganic. It does so by taking the resulting differential or ratio of energy absorbed, which is then associated with its chemical composition or atomic number. That result allows us to mask off organic items making the inorganic items pop.” Through product set up, operators teach inspection systems the uniqueness of specific product configurations enabling the system to recognize anomalies.

Eriez Magnetics helps tackle the challenges of pet food applications with a user interface similar to today’s smart phones in that it’s all icon based. “Overcoming different product variations starts with setting up the product,” Spurgeon says. “Eriez systems feature automatic setup through a full-color touchscreen that has a polar graph allowing an operator to visually see feedback from the metal detector. It’s not just values. It’s intuitive and simple to troubleshoot.” The system’s algorithm can detect a visual representation of the product and evaluate if it meets the target criteria and is free from foreign objects.

Addressing the challenge of product effects caused by moisture in pet food, the Interceptor metal detector from Fortress is designed to inspect conductive applications in paste, slurry or gravy form, helping to eliminate false rejects. The challenge is differentiating between the signal generated by the product as a result of moisture or mineral content and any metal contaminant. “The Interceptor transmits multiple frequencies at the same time which allows it to achieve much higher performance levels especially when inspecting products that have an effect due to moisture,” Gidman explains. “Compared to the traditional approach where inspection systems tune into specific frequencies, this method can identify the product effect and eliminate it from the higher-​frequency signal, where the potential effect of the metal is more prominent.”

A Mettler-Toledo X36 X-ray system inspects cans, cartons and metalized bags for metal, glass, bone and heavy plastic contaminants.
Gravity flow or throat detectors from Mettler-Toledo can inspect dry kibble products using Mettler-Toledo Safeline’s zero-metal-free-zone (ZMFZ) technology. This technology allows the metal detector to be close to other equipment and still accurately operate in plants with limited space. “Internal cancellation field (ICF) technology for highest sensitivity ICF is a special technique, patented by Safeline, that enables higher operational sensitivity settings to be used in close proximity to metal structures, such as weigh hoppers, metal chutes and forming shoulders,” Rogers says. “This technology enables the detector to locate small pieces of non-magnetic-grade stainless steel. The detector internally generates a secondary magnetic field that is opposed to the primary magnetic field produced by the detector. This technology prevents leakage of the primary magnetic field outside the detector, effectively suppressing interference from any nearby source including metallized film or aluminum foil.”

For detection technology to work intuitively, a system must be properly configured with the parameters for each individual product. Regular verification and testing is also important to ensure that contaminants don’t slip through undetected and that false positives don’t waste valuable product and cause production downtime.

Validated protection

Using preventive validation routines to challenge inspection equipment is an important part of pet food processing due diligence and quality control. “Testing should take place regularly — usually at the start and end of each production day — then hourly and between each product changeover,” Gidman recommends. “Intervals between tests need to be short enough that if a fault is found, products potentially affected have not left the facility and can be identified, quarantined and retested.” Third-party inspections are recommended annually at a minimum.

Many inspection systems automatically collect data. This supports reporting capabilities and assists in meeting the requirements of pet food safety programs and regulations. “Every event on the Eriez equipment is written to a log,” Spurgeon says. “An electronic paper trail is critical to ensuring a company has done their food safety due diligence.”

For best results update software when applicable and optimize the system for each new product or package configuration — similar is not good enough. “Take the time and effort to tune the equipment,” Thomas says. “Use the data that inspection equipment provides to make the process better, mitigate and fine tune where detection equipment can be placed for the best results.”

Confidence in the inspection equipment is critical. When the detector signals that metal is present, operations needs to be confident that the equipment did indeed detect metal. In other words, operations needs to be confident that it was not a false trip. “Brand image is everything, and that’s really in the end what this equipment and what Eriez does for our customers,” Spurgeon says. “We protect their brand.”