Metallic inclusions are the No. 1 contaminant in food products, causing product quality and consumer safety issues; however, the orientation of a metal contaminant can affect a metal detector, as the size, shape, and symmetry of metal contaminants cannot be controlled.

As an odd-shaped piece of metal passes through a machine in different orientations, the response to each one will be different. For this reason, we use spheres to test a metal detector: A sphere does not exhibit orientation effect and will always produce the same signal when passed through the same position within a metal detectors aperture. But if you flatten out the metal or roll it into a needle or wire shape, there will be a significant difference in signal, depending on how it passes through, due to the physics of disturbing the electromagnetic field.

The general rule for like metals is that if any of the dimensions are less than the detectable metal’s sphere size, the machine may have trouble detecting it in the hardest-to-detect orientation. Depending on the orientation in which it passes through, the signal will likely be much larger than that of the sphere.

These spherical test samples showcase advances in sensitivity and provide machine suppliers and buyers with a comparative benchmarking tool. They provide a solid and reliable gauge to measure machine sensitivity against. So, when a supplier reports a sensitivity improvement of 0.5 mm, this is a major concern.

Overcoming Orientation Effect

Orientation effect is a result of asymmetrical metal contaminant shards being more easily detected if they pass through the metal inspection system in one direction rather than another. Often, it’s easier to detect stainless steel and nonferrous wires when they pass through the aperture space sideways or upright, rather than in alignment with the conveyor. The reason for this is related to the magnetic permeability of the metal, which for stainless steel is much lower than for other metals.

One solution could be to position several metal detectors at various angles along the conveyor; however, this often results in a significant increase in aperture size, which diminishes the performance and sensitivity of the metal detector. Placing systems upstream throughout the process is usually more advisable.

Reducing the aperture size is another simple and effective way to increase metal detector sensitivity. Because sensitivity is measured at the geometric center of the aperture, the ratio of the aperture to the size of the product should be considered. Maximum sensitivity occurs when the contaminate is closest to the aperture walls where the electromagnetic field is strongest. It therefore makes sense that as the size of the aperture decreases, the performance of the metal detector improves.

During regular testing of food metal detectors, manufacturers should insert FDA-approved test pieces in various locations along the product—for example in the front, center, and back—and then run consecutive tests in which the metal sphere is travelling as close to the geometric center of the aperture as possible. These tests should be performed for all package sizes and configurations. This provides extra assurance that metal detectors are performing as they should, picking up the test contaminants, regardless of metal type, size, or product masking.

Know Your Metals

The type of metal contaminant also needs to be factored into the equation. All industrial metal detectors will exhibit a different level of sensitivity for the three main groups: ferrous (such as iron or steel), nonferrous (including aluminum foil), and stainless steel. Because metal detectors work by spotting materials that create a magnetic or conductive disturbance as they pass through an electro-magnetic field, stainless steel (300 series) is typically the most difficult to detect.

Figure 2. Stainless steel detection signals can be swamped by product effect in wet or salted products. Courtesy of Fortress Technology Inc.

Widely used in food preparation and production areas, stainless steel comes in various grades. The 300 series stainless steel is recommended for performance verifications, as it is non-magnetic and a poor electrical conductor, making it the hardest to detect. Consequently, a sphere of stainless steel hidden in a dry product typically needs to be 50% larger than a ferrous sphere to generate a similar signal size. This disparity can rise to 300% in wet products, such as fresh meals, meat, fish, sauces, preserves, and bread, because moisture in these products creates a conductive signal, and the metal detection can be swamped by product effect, which resembles the stainless-steel product effect phase characteristics.

Conversely, any product that is iron enriched, such as fortified cereals, supplements, or breakfast bars, creates a large magnetic signal that the detector must overcome in order to detect small pieces of metal. These are referred to as “dry” products and tend to be a lot easier in terms of detection capability, because there’s less worry about the product effect.

To identify a metal contaminant within conductive products, a metal detector must eliminate or reduce this product effect. The solution is to change the frequency of operation to minimize the effect of the product; however, when a metal detector’s operating frequency is altered, there’s usually a trade-off in performance.

Figure 3. The ratio of the aperture to the size of the product is an essential consideration as sensitivity is measured at the geometric center of the aperture. Courtesy of Fortress Technology Inc.

Simultaneous frequency is the most reliable way to remove product effect without compromising the sensitivity of a metal detector.

Finding Flat Flakes

Depending on how a metal flake is lodged within a product, there is also the potential for it to completely evade a metal detector by sneaking perfectly through the electromagnetic flux without causing a disturbance in the field. Inspection systems that use multiple oriented electromagnetic fields can cover each fields’ respective weakness; this technology is especially beneficial for upstream premium applications, such as confectionery and chocolate, and has proved to be reliable at detecting very thin flakes and foils that could be introduced in the mixing, rolling, scoring, molding, or baking processes.

Sphere Size Test Thresholds

The metal detection industry has general sphere size guidelines for food producers. These are based on whether the product being inspected is wet or dry, as well as the overall size of the product. For a wet block of cheese measuring approximately 75mm high, the sphere size parameters are currently ferrous 2.0 mm, nonferrous 2.5 mm, and stainless steel 3.5 mm.

Many variables can affect a metal detector’s performance, including orientation of contaminants, the type of product passing through the detector, product size, and even at times, the surrounding environment. Machine sensitivity remains a solid and reliable gauge, however.

As with any aspect of food safety, there’s always a cause and a consequence. The value of deeply rooted experience about how different food applications behave and change, about the conditions that cause these reactions, and about the relearning limits of inspection equipment, should never be underestimated.

Garr is a regional sales manager at Fortress Technology Inc.

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Preventing foreign object contamination is a growing priority for food processors. According to USDA, it accounted for more than 75% of the total volume of food recalled by the Food Safety and Inspection Service in 2019. Contamination isn’t a novel issue, however, and many processors are looking for new and innovative solutions to help automate detection and increase the likelihood of finding foreign materials. One reason for this trend is that materials such as plastics and rubber are showing up with greater frequency, and these materials are often missed by metal detectors and X-rays.

Improved detection of foreign contaminants will help reduce food waste as well as lower costs and the risk of recalls. Many processors look to identify contaminants early so they can address an issue quickly and minimize the impact on production.

The good news is that detection technology is evolving quickly. Vision-based systems are a good example of growing innovation in the processing sector. But what exactly do we mean when we talk about vision systems for food processing?

While X-rays and metal detectors are commonplace in processing, vision systems are relatively new. “Vision system” is an umbrella term for a number of different systems with widely varying capabilities and characteristics. In this article, we will compare different vision systems in terms of how they function, their specific attributes, and how they may benefit food processors.

The Science of Seeing

To understand the differences among types of vision systems, it’s useful to remember how light works—the science behind how we see things.

Our eyes are only able to see three color bands: red, green, and blue, otherwise known as the visible spectrum. However, light is actually made up of thousands of different wavelengths. Each wavelength behaves differently and interacts differently with various materials. We can use these diverse wavelengths of light, both inside and outside of the visible spectrum, to gather information about different materials or objects.

When it comes to comparing vision systems, there are three main differences to consider:

• The number of light bands, i.e., the number of colors that a system is able to see (otherwise known as wavelengths);
• The spectral resolution—the higher the resolution, the smaller the ‘gaps’ between each color or wavelength; and
• The amount of information a vision system is able to see per pixel of an image. A pixel is the smallest unit of information that makes up a picture.

Together, these three characteristics define the level of detail a vision system is able to consider, the ability of that system to detect a variety of different materials, and how “trainable” a system is, i.e., whether it can learn from the information it’s gathering.

The Art of Looking

The original vision systems are our eyes. Human inspectors are frequently brought in or added when there has been a contamination event. Studies from other industries have shown, however, that after just 15 minutes on an inspection task, human performance drops dramatically. After 30 minutes on a task, the probability of detection falls by more than 50% on average, meaning that inspectors have a one in two chance of missing the materials they’ve been hired to find.

This can be due to multiple factors, including line speed, levels of training or experience, fatigue or illness, and even external factors such as background noise or lighting conditions. Studies in other industries have shown that simply adding more inspectors does not necessarily increase detection rates.

Automation of repetitive tasks—such as inspection—delivers better and more consistent outcomes. It also frees up valuable staff for more important and, often, safer tasks that require human expertise.

Camera-Based Inspection Systems

Camera-based systems are the most well-understood type of vision system. Cameras have been around for more than a century, and most of us carry one in our pocket at all times. Camera-based inspection systems are the closest in performance to the human eye, which means that they will only see objects within the three colors of the visible spectrum. Their advantage over human inspectors can be greater consistency; they don’t get tired or lose concentration. However, cameras are not effective in detecting contaminants when there is little contrast between the object being inspected and the material they are looking for—for example, white plastic on a fatty piece of chicken or on ground pork trim.

Figure 1: Objects on
a busy background
(left) and on a plain
background (right).

When it comes to detecting contaminants, cameras will likely miss items such as clear plastics or any objects similar in color to the product. Line speed and lighting conditions can also affect camera performance, because cameras have trouble seeing things on a messy or variable background, such as meat on a line. Figure 1 shows how a camera can more easily see objects when the background is plain.

Camera-based systems are ideal for assessing size and shape, such as with nuggets or patties.

Beyond the Visible Spectrum

Multi-spectral systems are different from camera-based systems. Instead of being limited to three colors, as in a camera-based system, multispectral systems are able to see between three and 15 spectral bands, and can see colors outside the visible spectrum. This enables them to see some chemical properties of the inspected object.

Multi-spectral systems were used in early space-based imaging to map landscape details on Earth. Detection in these systems is based on the materials the system expects to see. In the case of space-based imaging, the systems were set to detect water versus land versus vegetation. In food processing, these systems can be useful when contaminants are consistently made of the same materials; however, new or previously unknown contaminants will be missed, even if this “new” contaminant reappears multiple times.

Because these types of systems use a set number of spectral bands, they have a limited capacity to learn from what they see over time. And, like camera-based systems, multispectral systems aren’t able to assess quality measures.

From Multispectral to Hyperspectral

As the name suggests, hyperspectral systems collect information across the electromagnetic spectrum. They measure continuous bands through both the visible and invisible spectra, which means they see hundreds or thousands of essentially continuous light bands. This means that hyperspectral systems gather very robust data about the materials being inspected, down to a chemical level.

Hyperspectral imaging systems produce incredibly rich data on every piece of product they inspect. In a food processing plant, that means you can not only find, but identify, foreign materials based on their chemical signature, reducing your time to resolve issues by pointing the way to the likely source of the contaminant.

Hyperspectral imaging systems can go beyond just finding foreign materials. Unlike multispectral or camera-based systems, hyperspectral systems can assess quality measures such as steak tenderness or fat/lean ratios in sausages and can find myopathies like woody breast or spaghetti breast in poultry.

Hyperspectral systems are also exceptional in another way: These systems can use artificial intelligence (AI) to learn from the chemical data they collect over time. This makes these systems highly effective at identifying new or unexpected contaminants. It also means these systems can grow and change over time as the needs of a processing plant change, without the need for new capital equipment.

Recent advances in computing and computer processing have made it possible for these hyperspectral systems to operate on the line in real time.

How to Choose a Vision-Based System

Vision systems have tremendous advantages for food processing, but it’s important to know which system is the right one for your plant. Asking the right questions will help guide your selection process.

Figure 2: Examples of detection curves for a hyperspectral
imaging system.

First, ask to see a detection curve for the system. A detection curve, a chart that shows object size plotted against probability of detection, will give you a very clear indication of how successful a system will be in detecting objects of any size. Figure 2 shows examples of detection curves for different materials identified by a hyperspectral imaging system.

A detection curve provides much more useful insight than simply asking about the smallest size of object a system can detect. A system that claims to find microscopic objects, for example, might only find them in very rare instances.

Second, ask about false positive rates. Using the same example, a system might claim to find a very high number of tiny objects. But what if many of these detections are false positives, meaning that there is no contaminant actually present? A lot of valuable product may be unnecessarily discarded.

Finally, ask if the system is future-proof. Will it be able to expand to detect new types of contaminants over time? Might you need to evaluate quality metrics in the future? Plants are constantly evolving, and new processing techniques or types of products bring in new forms of contaminants and evolving quality issues. Will the system be able to adapt to these changes?

The food processing sector is embracing innovation at a faster pace than ever before. But, as with any evolving technology, the key is understanding the differences among available detection systems. The right approach for your business may even be a combination of different systems—a multi-hurdled approach.

Asking the right questions will guide you in your selection and help drive efficiency and safety in the plant, while reducing food waste and costs in the long term.

Pawluczyk is chief executive officer of P&P Optica, based in Waterloo, Ontario, Canada. Reach her at olga.pawluczyk@ppo.ca.

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In March 2019, USDA issued a best practice guideline for meat and poultry producers to reinforce the requirement of notifying the agency within 24 hours of shipping products that are potentially contaminated with foreign objects. As the agency explained, although the rule had been in place since 2012, cases of foreign materials found by consumers had increased in recent years.

Foreign objects are an insidious issue for all food producers, not just meat and poultry processors. Unlike with pathogens, there is no kill step to eradicate or minimize the foreign object. Contaminations can occur at any point in the supply chain, with different materials and for various reasons: pieces of plastic from dough scrapers, bottle caps and golf balls, and broken metal from equipment or construction material are just a few examples from FDA’s product recall list.

Assessing Risk

The starting point to managing foreign objects in food production is to understand the hazards. “Risk is not a yes- or no-type question,” says De Ann Davis, food safety director at Commercial Food Sanitation in New Orleans. “Certain foreign materials present more of a health hazard than others. Some of them can be found readily through technology, while for others, like thin, clear plastics, it’s going to be very difficult.”

When you measure the likelihood of foreign object contamination, the quality of the information is important. “The best data comes from a strong near-miss program, which is a detailed library of materials found in partially or fully processed products before they end up on the shelf. Other important sources are your suppliers’ history and the validation of your own controls. It’s not just about how you can detect a piece of metal at the end of the line; it’s important to look at risk from a holistic standpoint,” adds Davis. The risk assessment will determine which foreign detection technologies to use and how to employ them.

You need a strong preventive maintenance program that avoids foreign material that may come off of equipment, such as pieces of conveyor belts, metal shavings, screws, or pieces of plastic. When foreign material is found on the equipment or within the facility, you also need a sanitation and GMP program that prevents it from entering the food-making process.—De Ann Davis, Commercial Food Sanitation

Sorters, Filters, and Magnets

Sorters, filters, and magnets are typically used with produce, powders, and liquids.

Produce is often washed first: “Water is a good segregation system because the produce usually floats, says Rob Kooijmans, CEO of the Food Strategy Institute in Amsterdam, Netherlands. “Wood floats on top and can be discarded later, soil dissolves, and stones sink.” In some cases, using magnets first might be a better option, as open fields could hide all sorts of foreign materials. That’s the case in the Netherlands and France, says Kooijmans, where it’s very common to find hand grenades from World War I or II with the produce.

A second, more sophisticated sorting level uses cameras, lasers, and infrared and ultraviolet (UV) radiations. “Cameras look at color and potentially shape, while lasers, infrared, and UV analyze reflection,” says Kooijmans. “By combining that information, you can detect foreign bodies that were not washed out in the beginning. A golf ball harvested with potatoes, for example, would float during the washing step and would probably deceive cameras and lasers too, but it will reflect UV light, while potatoes won’t.

Sieves are typically used with liquids and powders, while magnets offer a useful support, especially to detect any metal particles from grinding steel equipment left in dry powders, such as pepper and cocoa. “Sieves should be placed at the entry and exit of a processing step, because your process itself might introduce foreign objects. When only one option is possible for cost reasons, the best choice is the end of the line,” says Kooijmans.

X-Ray Systems and Metal Detectors

Metal detectors and X-ray systems detect foreign objects by recognizing the disturbance that they can cause to signals. In metal detectors, metal objects will change the electromagnetic field, generating a voltage signal; in X-rays, foreign objects with higher density will attenuate more energy, producing a darker area in the image.

The detection capability of both systems is limited by the so-called “product effect,” which can cause false positives or negatives. “In metal detectors, product effect is the phenomenon whereby the product and the contaminant generate a similar signal at the same frequency,” says Mike Munnelly, marketing manager of life sciences manufacturing at Thermo Fisher Scientific in Waltham, Mass.

The main cause of this product effect is the conductivity of the food, which can be increased by even the smallest variations in salt content, moisture, and temperature. Complex food matrixes make product effect even worse.

The most advanced metal detectors minimize the problem by using up to five frequencies at once. “Different metals respond better to different frequencies,” says Munnelly. With multiple frequencies, we can offer optimal performance. With just one, there is always some compromise to be made, maybe reducing the sensitivity to a particular metal in order to avoid product effect.”

Complex matrixes are a problem for X-rays too, due to their density profile. “With meat skewers, for example, detecting light contaminants would be much more difficult, as the wooden stick, the meat, and the vegetable oil would have different densities,” says Alex Kinne, an applications engineer at Thermo Fisher Scientific.

One solution is scanning products from different angles. “Using multiple beams greatly improves the chances of finding the most difficult contaminants, like glass inside of glass jars, that can hide at the bottom or in corners or edges,” says Kinne.

Another area of improvement for X-rays is imaging software that can differentiate between subtle changes in darkness: “It’s quite a difficult software to do well, but it has become more advanced over time, improving the probability of detecting contaminants,” says Munnelly.

Making Technologies Work Together

In general, each of these technologies has its own natural place in the production line: Sorting, filtering, and magnets only work with produce, liquids, or dry powders. Metal detectors and X-rays are better suited for constituted products. Their placement, however, is rather flexible.

“X-ray and metal detectors are used at different critical control points rather than in tandem,” says Kinne. “For example, in meat processing, metal detection may be used to inspect large oblong pieces of raw meat, and then X-ray after food is packaged.”

How you combine systems really depends on your risk, your food matrix, your line speed, and the capabilities of available technologies, says Davis.

For Munnelly, using X-ray, metal detection, or a combination of both depends on how “safe” food manufacturers want to be. “They could be guided by brand protection, a particular local regulation, or the request of a customer to use one or both of them,” he adds.

Investigating Foreign Object Findings

When a foreign object incident occurs, there are a few questions to answer as quickly as possible: What is it? Where does it come from? Why did it end up there? How much product could potentially be contaminated?

Investigation always starts in the facility, but it doesn’t necessarily end there. In some cases, food companies will resort to a lab to continue it with more sophisticated technology. “Whether or not a lab is involved depends on the impact of the incident,” says David Wright, associate principal scientist at Reading Scientific Services Ltd. (RSSL) in the United Kingdom. “If [a contamination] has gained media or regulatory attention, they’re likely going to investigate. When that’s not the case, then investigation is still advisable, as it allows the prevention of future, and potentially more serious, contamination.”

One risk of not conducting a deep analysis is misidentifying the material completely. “We had a case where a piece of suspected glass came in, which turned out to be an extremely hard plastic type. This might be unusual, but just highlights the fact that you might see something that it really isn’t,” says Rene Friedrichs, RSSL’s microscopy lab manager.

Identifying the type of material in a contamination is just the first step. You can obtain more useful information from a lab. “If a piece of glass was found by a consumer, we would determine [if] it’s a heat-resistance glass type from chipped kitchen glassware. In that case, it could have been unintentionally introduced by the consumer,” says Friedrichs.

RSSL’s microscopy lab use five technologies in particular, says Friedrichs:

• Light microscopy: Used to look at the morphology of the foreign material and to see whether there are deposits on it.
• X-ray microfluorescence: The standard technology to help identify types of glass, steels, and other metal alloys.
• Scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS): This technology can provide morphological and elemental information for even the smallest foreign materials.
• Fourier transform infrared spectrometer (FTIR): This technology can help to identify organic materials, such as types of fibers and polymers, by investigating functional groups.

The majority of foreign materials can be identified using some or all of these techniques. What tool to use will depend on each specific case. “We have a triage type approach where we make an initial evaluation of a sample using microscopy and then decide which analysis we regard as appropriate to correctly identify and characterize a sample,” says Wright. “If a foreign object is found in a packaged food, we will want to analyze the packing, as well, to help establish how it may have entered the product. We try to gather all the information and then decide the critical path: If it’s a piece of glass, it goes down one route; if it’s plastic; it goes down another. It depends on how we can find out what’s on the surface of something, what it’s been in contact with, and what else is around it.”

The benefit of engaging with a laboratory for further investigation is not just in the level of technology. “From our impartial, yet experienced, perspective, we will ask the right questions. When somebody is too close to a process, they might overlook what is actually quite obvious,” says Wright.

Prevention Is Always Better

In spite of the many technologies available, the best way to control foreign objects is to keep them out of the supply chain. “Before you think about the risk, you need a strong preventive maintenance program that avoids foreign material that may come off of equipment, such as pieces of conveyor belts, metal shavings, screws, or pieces of plastic. And when foreign material is found on the equipment or within the facility, you also need a sanitation and GMP program that prevents it from entering the food-making process,” says Davis.

“Too many companies just rely on their systems as if they were foolproof, but they’re not,” says Kooijmans. All these detection methods are trying to cure something that you should prevent in the first place. Prevention is always better.”

Tolu is freelance writer who specializes in covering the food industry. Reach him at andrea@andreatolu.com.

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Food contamination caused by bacteria or chemicals gets most of the attention when it comes to news stories. In 2018, the main headline-grabbing contaminants were Listeria, Salmonella, and E. coli—all three of which prompted recalls that included cheese products, salads, meats, and pet foods.

Because third-party X-ray inspection services are dedicated entirely to inspection, they operate at a much slower speed to allow technicians to monitor each item individually.

While recalls due to such bacterial contamination get a lot of attention, the fact is that the presence of foreign material in food continues to be a larger growing problem. It’s a significant enough problem that, on March 8 of this year, the USDA Food Safety and Inspection Service (FSIS) announced a new guideline for the meat and poultry industry dealing with customer complaints in direct response to contamination from plastic, metal, and other foreign materials.

Those new guidelines require contamination incidents to be reported to the FSIS within 24 hours.

The government agency says it renewed its emphasis on responding to complaints of foreign materials following dozens of complaints and recalls last year due to foreign contamination in chicken, sausage, and other meat products.

Are Contaminants More Common, or Are We Better at Catching Them?

As the number of reported incidents continues growing, many consumers question what’s going on with the food supply. Are there more instances of contamination, or does our 24/7 news cycle just make sure we’re hearing about them?

The truth is, it’s probably a little bit of both. The industry has become more sophisticated in its ability to detect contaminants, whether they are biological, chemical, or physical. A September 2018 story on National Public Radio’s Morning Edition noted that then-FDA Commissioner Scott Gottleib believed today’s food supply is safer than ever; what has changed is our ability to identify threats to our food and stop them from reaching consumers.

Preventing food contamination by foreign materials begins with understanding where the danger lies. There are a number of different ways for contaminants to enter the food supply, and as our food chain becomes increasingly global, those entry points continue to grow. Any time a new ingredient is introduced, from the field to the final stage of packaging, it also introduces a new opportunity for physical contamination.

Among the many sources of foreign contaminants in food products are pieces of manufacturing equipment, such as a blade, a wire, or a cracked gasket, that fall into the food. They can come from employees losing objects like an earring or a pen; a broken glass during packaging can also contaminate product. Or, it might come in the form of a rock or pieces of wood from where the food product or ingredient originated.

Further adding to contamination is the growing use of plastic materials. Today, plastic and rubber are two of the most common materials used in a food manufacturing plant—and while that makes the process easier for manufacturing in many ways, it has also created new headaches for food producers. Recently, two of the largest meat and poultry producers had to conduct recalls on their products, which totaled almost 100,000 pounds, due to rubber contamination.

Regardless of what type of physical contaminant it is or where the contamination occurred, the time to correct it is before that product hits the shelves and reaches consumers. Today’s increasingly sophisticated detection systems are designed to do just that.

Finding Foreign Materials in Food

Today’s food manufacturers have many choices when it comes to the type of equipment they use to safeguard their food. One of those options is X-ray inspection.

X-ray inspection machines have the ability to find all types of foreign material, including metal, bone, plastic, glass, rubber, wood, and more. The machines use a detector and programming algorithm to reject potential foreign contaminants based on a difference in their density. Since they are able to detect all types of foreign objects, they’re particularly effective in food manufacturing environments.

Even within the category of X-ray inspection machines, there are certain differences to consider. Inline X-ray inspection machines typically use flat-panel technology and are small enough to fit into the body of the inspection machine. They’re similar to the equipment used by the TSA for baggage screening at airports and will flag the presence of foreign materials, but they have certain limitations due to the speed of the production line and the power of the X-ray.

Since a food manufacturer may be running thousands of pounds of product per hour, inline machines aren’t able to typically keep up with the speed of production and likely can only alarm that there is a problem. That, in turn, means the indication of foreign material can cause the quarantine of thousands of pounds of product. At the same time, the higher rate of speed combined with operational desensitization to limit a higher rate of defaults can also keep the machine from detecting smaller contaminants, such as those less than 3 to 5 mm.

These machines let manufacturers become aware of the presence of foreign materials, allowing food producers to decide what their next steps will be to prevent the contaminated product from reaching consumers.

Third-party X-ray inspection services are a supplement to existing screening and detection methods, not an alternative. When an inline machine flags a problem, a third-party X-ray inspection service can then work through the quarantined product to find the contaminated product faster and more affordably than any other option. Dollar for dollar, it’s less expensive to have the product examined by a third-party service than it is to try reworking the product in the existing facility, to dispose of the full production run, or to risk a lawsuit or recall.

Because third-party X-ray inspection services are dedicated entirely to inspection, they operate at a much slower speed, which allows technicians to monitor each item individually as it passes through the machine. In a food production environment, it’s not feasible to have a designated worker visually watching a screen to look for contaminants. The speed of the line makes this an impossibility, but for a third-party inspection service, such monitoring is critical and is more effective.

For example, FlexXray’s custom X-ray inspection machines can detect multiple contaminants as small as 0.8 mm (or even smaller in most cases), and line technicians are trained to notice issues and changes in density that signal the presence of foreign material contamination. When such a change is noted, the technician can stop the line and zoom in on the area in question for a magnified image. If identified as a foreign contaminant, the product in question can be immediately removed from the line and segregated from the saleable product for safe and proper disposal.

Foreign material contamination issues aren’t an isolated problem—they’re something that every food manufacturer faces. Knowing your options and having a plan in place to resolve an issue when it occurs is the best insurance to avoid a costly recall or lawsuit and to keep business operations running smoothly.

Keith is the vice president of sales, marketing, and customer service at FlexXray. Reach him at ckeith@flexxray.com.

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Imagine watching the news and a story entitled “Check your fridge and pantry for food products recalled this week” brings up a picture of your brand’s packaging. It’s not that uncommon. For example, in late 2018 one manufacturer recalled 29,028 pounds of frozen, ready-to-eat poultry and pork sausage links after five people called USDA’s Food Safety and Inspection Service to let the agency know they found metal pieces in their sausage.

While regulatory pressure and the risk of financial loss have pushed many manufacturers to invest in detection technologies, mitigating risk entirely remains a challenge. Thankfully, today’s metal detectors and X-ray detection systems offer higher levels of sensitivity, but that wasn’t always the case, and not every manufacturing facility has the latest technology.

This article will explore the evolution of metal detection technology for food safety. Metal detection systems provide reliable, cost-effective protection from even the smallest metal contaminants found anywhere in a food production process. They can also help improve operational efficiency and eliminate expensive downtime, service costs, and repair bills. And metal detectors are suited for a wide range of demanding food processing applications and packing environments.

Metal Detector Technology

Metal detectors are common across food processing facilities to meet HACCP (Hazard Analysis and Critical Control Point) requirements. Most often they are placed at the end of the line as the last defense against escape before a packaged product is sent on its way to the consumer. The core technology, though, has always had limitations, such as the so-called “product effect,” where a detector cannot differentiate between a conductive product or one with high mineral content and the metal contaminant and susceptibility to “noise” coming from many possible sources in the typical harsh, industrial food production environment.

Basic metal detector technology relies on coils that are wound on a non-metallic frame and connected to a radio frequency transmitter and receiver. The transmitter “excites” any unexpected metal objects and generates very small changes in return signals to detect foreign contaminants. Digital signal processing algorithms are used to differentiate between the expected product signal and that of an unexpected foreign object. The technology works, but historically performance can be inconsistent and sometimes even unpredictable. Recently, with the introduction of multiscan metal detection technology, this is starting to change.

The Evolution of Frequencies

Early metal detection technologies for the food industry were limited to single, fixed frequencies. A manufacturer could best detect a piece of stainless steel using a high frequency, but when a wet, warm, or salty product was introduced it would be forced to reduce the frequency and thus the sensitivity due to the product effect. This simple frequency change required setup by skilled technicians who might spend hours selecting the “best” frequency for detection of all metal types. A user could not make this change themselves.

Single, fixed-frequency metal detectors had limitations for the typical food manufacturing environment given the range of products to be tested and the variability of metal contaminants that could enter the process. That’s why manufacturers started adding second and third frequency choices (always running just one frequency at a time), giving users more flexibility. Manual frequency switching became more common but was only marginally less onerous: Expertise was still needed to optimize detection. Nonetheless, this was an advancement since it introduced more frequency flexibility to metal detection.

The next advancement in metal detection was the development of frequency selection via software. The “best” single frequency for a given application could then be selected prior to production by scanning a product many times and testing detection. This was known as variable frequency metal detection, and it enabled setup without the need for a specialist. Manufacturers still were forced to live with the “best” single frequency compromise, however, and accept its lower overall performance.

A recent advancement in metal detection enabled detection at two frequencies simultaneously, essentially performing like a low and high frequency detector in one. Although the dual-frequency metal detection approach improved overall sensitivity, the combination of frequencies that could run simultaneously was still limited. The opportunity to miss metals with frequencies between or on either side of the dual setting still led to compromise that left quality managers wanting more.

The Advent of Multiscanning

Multiscan technology is said to be the long-awaited innovation in metal detection. Metal detectors with this capability can identify contaminants that are up to 50 percent smaller in volume than previous technologies, including food items with high product effect. With multiscan technology, the CCP can scan up to five adjustable frequencies, raising the probability of detection exponentially. Essentially, it’s the equivalent of having up to five completely adjustable metal detectors back to back in a production line.

Multiscan detectors don’t continuously broadcast the five frequencies simultaneously. If they did, the power requirement would be too high and expensive. Instead, the frequencies are scanned thousands of times per second, equivalent to broadcasting simultaneously without requiring as much energy.

Another benefit of multiscan technology is complete flexibility to set frequencies and the associated detection parameters. This is important given that the interaction of the product and metal in all applications is different, depending on factors such as the ingredients in the product, the type of packaging, the product temperature, and variation in all of the above. Most times these interactions are impossible to predict too. With multiscan technology users can make changes in software, selecting the appropriate five frequencies in the 50 to 1,000 kHz range. If a quick test shows detection for an application is best in the 400 to 600 kHz range, the user can easily select five frequencies in that range to maximize performance. To counteract product effect, the user can simply select a lower frequency range, such as 100 to 250 kHz. Different combinations can be selected for different products and they can be changed at will at any time. Multiscan detectors are based on the idea that there is no perfect frequency, and that the best range of frequencies changes depending on the application.

A not-so-obvious benefit of multiscan technology is that it can be used to address an all-too-common metal detection problem–electromagnetic interference (EMI), which can happen in almost any factory at any time. EMI is an invisible field typically generated by a motor or variable frequency drive that moves through the air into the metal detector aperture, causing interference with the detection signals. EMI can come from a variety of other sources in a harsh industrial setting and the aperture can’t be shielded because it’s where the products pass through. Users can simply look at the screen on an advanced multiscan detector to see which frequency or frequencies are affected by EMI and adjust accordingly. This can be done in a matter of minutes and doesn’t require a specialized skill set.

Finding the Best Metal Detection Solution

There is no “one size fits all” approach to metal detection. The best protection against metal escapes is ensuring that the solution you implement is the right one for your products. Even with advanced multiscan technology, it’s critical that manufacturers consider their unique systems, processes, equipment, and product types before making a final decision about which technology to deploy and how.

To ensure future detection performance, a best practice is to have the metal detector manufacturer conduct controlled tests on the detection equipment of interest. The test must simulate, as closely as possible, how product will ultimately be inspected on an actual processing line. Product-specific factors such as temperature and package configuration must be replicated.

While no product test can replicate actual conditions, the more rigorous the test, the better. A testing process should specify performance requirements to provide confidence that the inspection solution will be suited to a specific application. Even for an advanced metal detector, such as one with multiscan capability, it’s important to follow a strict process to ensure each requirement is addressed. At a minimum, the testing should consider the following.

Product presentation and orientation. Results could be invalid if the product passes through the metal detector in the wrong way.

Production conditions. Temperature, pitch, and speed should match the actual production environment. Because temperature affects the electromagnetic signal given off by products, failing to factor in the unique signal of a hot versus cold product on a production line would lead to false rejects. Pitch should also be tested to understand the total amount of signal in the detector at any time and how many products might be detected at a time.

Placement of metal. Testing should be performed by placing metal in multiple locations on a package, including the center of the aperture, the weakest detection point because it is the farthest away from the metal detector coils. A thorough assessment should include tests on leading, trailing, absolute center, and sides to ensure metal is detected anywhere in the package.

Analysis of results. After testing is complete, a formal report should provide recommendations for each tested product, including recommended conveyor speed, frequencies, and setup parameters.

Finding the best metal detection solution is certainly easier than it once was. The most advanced instruments are now more reliable and versatile, bringing greater efficiency to manufacturers while requiring fewer trade-offs. It’s possible to have confidence, high throughput, and flexibility at the same time. Today, the high bar is multiscan technology, yet future advancements are inevitable. It may never be possible to make escapes 100 percent preventable, but today’s technology—supported by best practices—is already saving millions for manufacturers by avoiding costly recalls and, most importantly, ensuring food is safer for consumers.

Ries, the lead product manager for metal detection and X-ray inspection at Thermo Fisher Scientific, advises customers on specifying, installing, and using metal detection and X-ray systems to improve food safety and quality. Reach him at Bob.ries@thermofisher.com.

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No day is a good day for bad news but it has often been said that a Friday afternoon is the most likely time a food manufacturer will get the first official notification of a product contamination. The number of food product recalls in North America, Europe, and Australasia have been growing for years. From 2015 to 2017, plastic and rubber contamination events increased recalls by at least one-and-a-half times. The most frequently reported recalls for plastic and rubber contamination are the food sectors that use higher levels of mechanical methods, such as poultry and red meat processing, cereals and bakery, and confectionary.

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(Editor’s Note: This is an online-only article attributed to the June/July 2018 issue.)

With over 23 years’ experience in food manufacturing, including holding various roles in quality assurance for several Fortune 500 companies, the one thing that always surprises me is that many manufacturing facilities still get customer complaints for metal in their products even though the companies have systems in place to prevent foreign material contamination. It begs the question, how can metal get through their process with metal detection equipment in place?

How Do Metal Detectors Miss Metal?

Production line in the food factory.
Image Credit: IP Galanternik D.U./iStockphoto

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(Editor’s Note: This is an online-only article attributed to the February/March 2018 issue.)

Seems like just yesterday, I found myself answering a customer complaint for a chipped tooth.  As a prior vice president of quality at a large food manufacturer, I asked myself how could a person chip a tooth on a piece of food, given all the great foreign material prevention programs my company had in place?

Third-party auditors gave my company high marks for its food safety programs. Though the company received high scores, I wondered if it could do even better. Programs were in place for analyzing hazards, internal standard operating procedures, and supplier approval programs—all designed to protect the customer. Filters and metal detectors were installed on manufacturing lines to identify foreign material and help prevent it from getting into the food. However, all the technology and programs did not prevent the inevitable based on customer complaints.

A consumer “claimed” he cracked a tooth on a stone when he took a bite from a food product.  Being the VP of quality, I put a great deal of thought into it but based on the limited information, I could not ultimately prove the crack was, or wasn’t, caused by the company’s product.  What I did know was that a person was injured, possibly as a result of a product my company manufactured. The product was made with real potatoes, which are grown in the dirt—yes grown in the dirt with rocks and other organic and non-organic materials along with whatever else ends up in the farm field where the potatoes are grown.

This potato incident had me asking about the company’s manufacturing technology. Despite various efforts and all the programs in place on the lines to protect the final consumer and assure a safe-quality product, it seemed that the systems had potentially failed in one instant.  Not only did I feel personal responsibility to investigate this further, I wanted to get my arms around the extent of the problem—how widespread it might be within the company—to better understand how often this might be happening to other consumers.

I began to investigate the overall customer complaints for these types of company products and found that this was not the first time a customer had complained about a rock or other hard object in their food. In fact, it happened to be the most common complaint for foreign material.  This made me wonder how many more companies and products made with “real” ingredients may have similar issues and how this can be prevented by the manufacturers.

Getting Pro-Active Using X-ray Technology

This was the first time I investigated X-ray technology for this specific process.  I had previous experience using X-ray technology to investigate known incidents, but I was reacting to the situation and not being pro-active.  X-ray technology was available, but it was much more expensive than the standard metal detection systems the company had in place. In fact, it was between five and 10 times the cost depending on the type and quality level of the machine. But what is the cost of protecting your brand and the health of your consumers? Most people will agree that protecting the customer, the brand, and the overall company reputation is the most important thing, even beyond the money.  It might seem like an easy answer from a logical standpoint—that manufacturers would use the best technology possible to prevent foreign materials in product. However, the answer is not always so simple.

Responsible Decisions

As a manufacturer, there are many things that come into play before making a capital purchase to improve the technology from standard metal detectors to X-ray.  A plant may have line constraints that prevent expansion such as spacing to fit the technology; line speeds that may not work with the new technology; and cost limitations, which may prevent adding the technology.  I have even heard manufacturers state that “there is not a return on investment” for X-ray if they only have to pay out a few thousand dollars a year on medical expenses for cracked teeth or other injuries versus paying hundreds of thousands to install X-ray technology.

This is similar to when an automobile comes out with better technology from a safety standpoint and all the old vehicles don’t upgrade to the technology, or only the high-end new vehicles incorporate the latest technical advances.  The consumers may choose to add the new features, but at a cost. You may think it would be standard for everyone to have back-up cameras on their car to prevent running over a toddler in the driveway, but that is not always the case.  In the camera scenario, the consumer gets to choose.  In foreign object control for food, the decision is left to the manufacturers.

Customers put their faith in the producers and trust they will make a safe-quality food using the best technology possible.

The government (FDA, USDA, etc.) does not specifically mandate technology or tolerances acceptable for foreign material in foods.  They have limits for things such as choking hazards and standards for what would be considered product adulteration. However, the trust and responsibility lie in the hands of the manufacturers to protect the consumer.

What’s in Your Food?

People have laughed when I asked them, “What’s in your food?” They usually respond by saying the ingredients. Seldom have I heard them say they found foreign material in their food. However, it is not uncommon for a consumer to find small bone chips in meat products, stones and glass in agricultural products, and dense brittle plastic in other manufactured items. When I share this information with them, it often comes up that they do remember a time when they had a foreign material incident in their food. It may have been a bone chip in a ground sausage product or a stone in their lentils. It may have been a piece of paper or plastic they found. They may not have been injured, but it did create a memory that they will carry with them for a long time.

As manufacturers, we want our customers to have only positive memories and experiences. When a consumer has a negative encounter with a product, we want to do everything possible to resolve the issue and make the customer happy.  Sometimes it involves addressing a perception that the customer has acquired, and we can help shape their thought process in a positive direction. But when it comes to foreign material, there aren’t any customers who would say we could change their mind and get them to believe that a small amount of foreign material is acceptable in their food.

As for X-ray technology, it is not a catch-all and it is not 100 percent fool-proof. In fact, for certain metal conditions it may not be as sensitive as a standard metal detector. However, there are multiple things that X-ray can do in combination with other programs and food safety tools to help ensure the customer receives a safe-quality product.  X-ray not only helps in identifying foreign materials, but is can detect missing components, determine mass/weights of product, and find cracked/misshapen products, along with other uses.

Many Fortune 500 companies and other progressive companies are installing X-ray machines to help detect foreign material in their process. Just like with any technology, it will take time for it to become an industry standard, but I can see a future in which all food manufacturers will be using this technology to help prevent their own consumers from chipping a tooth.

Hetherman, an operating partner in X-ray inspection for food at Service Cold Storage, has 22 years of experience in the food manufacturing industry. Reach him at chetherman@servicecold.biz or 715-600-4657.

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More stringent measures in the production process have led to a greater emphasis on the hygienic design of production line equipment. The trend in the general food sector is to purchase equipment that has been smartly designed to incorporate both hygienic construction and the challenges they face in terms of product handling.

Image credit: Eagle Product Inspection

Many of the applications are in the meat and poultry industry—predominantly because in many cases other types of foods go through secondary processes prior to the product reaching the consumer. These processes, that may include cooking, reprocessing, or significant alteration of the raw material, often help to sterilize the product.

For meat and poultry, a large percentage of products are provided to the consumer in the raw state. They will go through a series of processes that will alter form, such as grinding for hamburgers, or deboning and trimming chickens, but those items that are reaching consumers are still raw and haven’t usually been secondary processed.

What is Hygienic Design?

The latest guide from the Foundation for Meat and Poultry Research and Education, which was produced from their Equipment Design Task Force in 2014, can be found on the North American Meat Institute (NAMI) website. In terms of sanitary design principles, it is an ideal workmanship style document that outlines what sanitary design should mean both to a customer and a manufacturer. It is a good roadmap for suppliers to be able to look at the design and to quantify whether a system is going to be compliant with these design best practices.

Machines built using sanitary principles such as those provided by NAMI and the Sanitary Equipment Design Taskforce are designed so they meet a set of industry driven criteria that quantifiably defines sanitary construction. This includes such topics as the types and finishes of materials to be used and elimination of harborage areas where product can accumulate and create a microbiological risk. But the specifications are also very operations-centric providing guidance on best practices for inspection, maintenance, and cleaning protocols. The continuing challenge to manufacturers is to define what is the right amount of hygiene and sanitation for their specific operation and environment while still being profitable, protecting the consumer and the brand while complying with governmental standards and regulations.

In theory, every supplier of product inspection equipment should be able to design a device to perform a certain way at a specific point of time in a given environment. What’s difficult is to keep that performance consistent and within specification for long periods of continuous operation. Hygienically designed systems must be built to last—especially given the rigors and conditions of the meat and poultry industry and they also must perform their inspection tasks as specified throughout their useful life. Therefore, the overall robustness of the entire system is extremely important.

Where inspection is concerned, precision X-ray technology performs best when applied in a well-defined and controlled manner. When the necessary robustness required for the environment and operational longevity is added in, these two things may appear to be in conflict. Robustness and precision do not necessarily go hand-in-hand but are not mutually exclusive either, they must be balanced carefully with each specifically addressed. In an X-ray system, for example, there is a generator, which produces a beam that is shot through a window, through the product, through the conveyor, and then through to the detector, all contained within a housing to prevent X-ray emissions. When addressing sanitary design both inside and out with the need to clean machines rigorously every day, it should be done while maintaining the integrity, the technology, and its safe operation. Good design practices take these varying requirements into account with the manufacturer integrating them into a solution that effectively satisfies the needs for hygiene, longevity, and precise inspection.

In most cases, product is being inspected anywhere from 100-200 feet per minute in an environment that is wet from the product and periodic washdowns, creating a challenge to keep the conveyors moving and transporting product day in and day out. Like the design of the X-ray generator and detector assembly, the same rigor must be applied to the material handling and reject sortation system.

Other external influence factors around the machine such as floor and adjacent machine vibration and cold air handlers that can cause significant changes in temperature as they cycle on and off can impact machine performance, so it’s important to consider the surrounding area to mitigate those external influences before finalizing the machine placement to ensure a successful installation.

Benefits of Hygienic Design

It may be obvious to say, but the more hygienic the design the less the risk manufacturers have of an event occurring where the machines themselves contribute to it. When considering equipment purchase, customers should be encouraged to sit down and review the designs and to carry out their own scoring. If there is no set method of scoring within their business, the guide previously referred to from the Foundation for Meat and Poultry Research and Education and found on the NAMI website is easily accessible and can be invaluable in the decision-making process. An educated customer—particularly when it comes to the principle of hygienic design—will see the benefits of procuring a system that has been designed specifically for its environment. Of course, many customers are aware of what’s required already, but sometimes there is a preconception that inspection technologies need a “hall pass” when it comes to hygienic design and that there must be a compromise to achieve the desired inspection results to the detriment of the hygienic element. This is not always the case, as a system designed from the ground up to the specification can meet most of, if not all of the check boxes required. Just because it’s an inspection technology doesn’t mean there should be a compromise on standards.

Machines built to strict industry standards are designed to minimize and eliminate harborage areas where product can accumulate and create a microbiological risk, but the design must also be very operationally-centric, providing methods for user operation, maintenance, and cleaning. The continuing challenge to manufacturers is to define what is the right amount of hygiene and sanitation for their specific operation and environment while still being profitable, protecting the consumer and the brand while complying with governmental standards and regulations. Needless to say, when most consumers are shopping for dinner they don’t understand what it takes to produce a pound of ground beef—not least to produce it and still only charge $3.99 a pound, make a profit, and stay in business to continue to produce enough to meet future demand.

IP69 Doesn’t Guarantee Hygienic Design

Although hygienic design is paramount in the meat and poultry sector, due to the raw element of the product and the frequent washdown requirements in the harsh environments, the food sector in general is making it much more of a priority.

Things such as ease of cleaning are very important, as is ensuring there are no areas that could trap contaminants or microorganisms, and these challenges should be addressed at the initial design stage. Part of the process for sanitary and hygienic design is making sure the machines are easy to inspect once cleaned to ensure the process has been carried out completely. The latest systems enable line of sight inspections that do not take long at all—leading to further time and therefore production savings.

Many associate hygienic design with IP69 ratings, but these are often confused. IP69 and hygienic design are not the same thing. Having a system with an IP69 rating does not mean you have a hygienic machine. It is purely an ingress protection rating. It has nothing to do with the sanitation of the machine and how well it has been designed in terms of hygiene. It simply ensures that cabinets and enclosures will not leak when washed down to that specification. For instance, Eagle has machines that are IP69 compliant that are not hygienically designed—whereas nearly all of the hygienically designed machines are IP69 compliant. It is important to understand the difference.

Correct Approach to Design

It is far better to have a machine that is designed specifically for purpose using specific guidelines, such as NAMI, NSF, and European EHEDG. This way, customers can be supplied with a robust product that is designed to most closely match their purpose. If you compare a product designed in this way to one that has been adapted, the differences are very noticeable. Of course, an adapted machine will be cheaper, but in the bigger picture a machine designed for the application will have a far more attractive total cost of ownership, and will deliver a far bigger incremental value to a customer.

How long do you want a machine to last? That is the question. If you have to decommission a machine four years into a seven-year depreciation cycle, then that’s a fairly large hit to take financially. But there are other things such as cleaning cycles that are important to consider. These machines are cleaned on a daily basis—often multiple times—so to have a machine that has been designed to be disassembled, cleaned, and ready to be sanitized by one person in a matter of a few minutes is highly desirable. Most machines require two people to tear down and it takes longer. Subsequently it takes longer to put it back together. The time saved in man hours over the course of the machine’s life alone is significant, coupled with the uptime advantages associated with those hours makes for a very attractive proposition.

Working with an expert supplier to talk through requirements and to cover all available options is the first step to take when considering the purchase of a hygienic product inspection system. It’s not all about the initial investment. There is a far bigger picture to take into consideration, and in doing so manufacturers can ensure the protection of both brand and consumer, at the same time making considerable savings.

Thomas is strategic business unit manager at Eagle Product Inspection. Reach him at kyle.thomas@eaglepi.com.

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