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Kim Durkot Joined Thermo Fisher Scientific in November 2021 as field marketing manager for the Product Inspection business. In this feature, she explores how rising food recalls are driving retailer-specific inspection standards in the EU and US, with foreign object detection technologies like metal detection and X-ray inspection at the forefront.

As manufacturers are keenly aware, food recalls can have a major impact on reputation and profitability. Experts estimate direct costs to be in the region of $10 million with indirect costs potentially much higher and longer lasting. As food recalls rise across the EU and US, food retailers are becoming increasingly aware that they too are exposed to these negative impacts.

The result is a growing trend towards retailer-specific inspection standards; meeting them is becoming a condition of access to the markets that leading retailers gatekeep.

In the UK, for example, Marks and Spencer, a company renowned for the strength and quality of its food offering, has established a range of stringent inspection requirements that are seen as the gold standard within the industry. US retailers are progressively following suit, leaving suppliers with a choice between compliance or the risk of losing valuable on-shelf placement.

In this article, we explore strategies for tackling foreign object contamination, one of the top three causes of food recalls, responsible for ten out of 65 USDA product recalls in 2023. We delve into two key technologies – metal detection and X-ray inspection – offering guidance on what to look for in both systems and suppliers. This practical introduction is designed to help manufacturers stay ahead of the curve in meeting the increasingly stringent expectations of food retailers.

The challenge of foreign object detection

The range of physical contaminants that can enter the food supply chain is highly varied as evidenced from product recalls from the USDA and FDA archives, which include:

• Metal fragments in the sugar topping of baked items

• Pieces of glass in cashew snack packages

• Hard plastic and metal in raw pork chorizo

• Rocks in chicken pilaf

The size and nature of contaminants along with the properties of the food and its packaging all influence detectability. For example, the high conductivity associated with salty or moist foods can be problematic for certain technologies while metallicised packaging may be a complicating factor for others. The need to detect at speed, to avoid disrupting production schedules, is crucial and the levels of sensitivity required can be demanding.

Metal detection and X-ray inspection, together, answer directly to these challenges and are the front line ‘go to’ solutions for foreign object detection. Let’s take a closer look at their strengths and limitations.

Metal detection: How it works, and key system features

Metal detectors find both ferrous and non-ferrous contaminants, including aluminum and stainless steel, with balanced coil designs dominating the commercial landscape. Metallic particles passing between conducting coils disturb the field induced by a high-frequency radio transmitter, changing the voltage between the coils by a few microvolts (see figure 1). The resulting signal allows the instantaneous detection and rejection of contaminated product in accordance with well-defined threshold values.

Metal detectors are flexible, cost-effective and sufficiently robust to ensure long-life in most process settings. Systems operate over a wide range of speeds, detecting at either single or multiple frequencies. Metal detector technology is suitable for both packaged and unpackaged products but works best for dry, inert products that are unpackaged or where packaging is non-conductive.

That said, multiple frequency systems can handle wet, conductive products and, more broadly, deliver to higher performance standards.

In addition to setting specifications for size and sensitivity, retailers are looking for highly reliable, consistent, and assured contaminated product removal. Standards may therefore extend to how the system ensures contaminated product rejection, fail safe conditions, auditing, and recording capabilities (see figure 2). Features that may prove essential to meeting such requirements include:

• Failsafe sensors, complete with alarms

• Automatic rejection with lockable reject bin incorporating bin open/unlocked alarms and bin full notification

• Full enclosure between inspection point and reject bin to prohibit contaminated product

• Photo eye for pack registration

• Additional alarms, for example, fault detection, reject confirmation, air pressure failure, reject device failure; both visual and audible alarms may be required.

X-ray inspection: how it works and key system features

X-ray inspection systems detect a wide range of solid contaminants, including metals but also glass, rock, bone, and plastic. X-rays penetrating a product lose energy, with contaminants augmenting the effect. Conversion of the detected energy signal therefore reveals contaminants in the form of darker, shaded areas. Figure 3 shows the key features of an X-ray inspection system.

X-ray inspection systems are best used for conveyor or bulk inspection. Dense, highly textured products are the most challenging for X-ray inspection technology, but performance is dependent on both the hardware and software used.

With the right solution users can detect a wide range of contaminants with high sensitivity, in a diversity of packaged products including metal cans, glass bottles and products packaged with metallicised film or seals. Tuning sensitivity to ensure effective screening while avoiding an excessively high false rejection rate is critical for successful implementation.

It is important to note that X-ray inspection systems use high voltage X-ray tubes, rather than radioactive materials, to generate X-rays and that the FDA indicates no known adverse effects from consuming products subject to such screening. That said, it is important to purchase systems from a reputable supplier that meet the necessary standards: the US FDA Code of Federal Regulation 21 Part 1020.40, for example, or UK IRR 1999. Regular maintenance including the checking of safety switches and radiation shielding curtains is also advised.

Beyond technology

While retailers may be setting the standards for foreign object detection it is the choice of technology and supplier that will determine the cost of meeting them over the long term. The upfront capital expenditure associated with implementation is relatively easy to assess but total cost of ownership, over a 5-10 years window, is arguably the crucial figure.

A system ill-matched to product requirements, poorly engineered, inherently unreliable or ineffectively maintained will be unlikely to meet uptime requirements. When unplanned downtime triggers the cessation of product shipping any differences in purchase price can quickly become dwarfed by lost revenues.

To ensure procurement of an optimal long-term solution consider the following questions:

• Which detection technology can deliver the sensitivity and accuracy required for your application?

• Does the proposed solution offer the design, configuration and flexibility needed for your specific processing environment?

• Does the equipment have a track record of performance, longevity and reliability?

• Can you access expert application, commissioning and troubleshooting support, should you need it?

• Is maintenance proactive or reactive? If there is a problem what services and supplies are in place to ensure a speedy resolution?

• Are replacement parts, of certified quality, available on demand?

• Can you access training now, and into the future, when you have new recruits?

• Can you spread the cost of servicing and maintenance in line with your needs?

Retailers acting to protect themselves against the negative impacts of product recalls are boosting the imperative for foreign object detection to exacting and specific standards. Working with established, trusted vendors that are well-versed in meeting stringent and specific retailer requirements allows food manufacturers to respond confidently, effectively and cost-efficiently to this challenge.

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