X-ray inspection uses the fact that different atoms absorb X-rays to differing amounts. Therefore, protein will appear differently in an image to metal, bone or glass. The darker regions caused by these foreign objects can then be detected using image analysis software — and any product showing signs of contamination can be immediately removed from the process. As well as detecting a broad range of metallic and non-metallic contaminants, X-ray inspection can also use the generated image to count products, check product mass and carry out numerous other quality checks.
However, when poultry products can take such a wide range of forms — from nuggets to whole birds — how can manufacturers implement X-ray technology while minimizing waste? A single approach will not work for all products, so multiple tactics are needed.
For bone-in products, the approach is straightforward. Here, we can inspect as late in the process as possible — ideally once the product is sealed, to prevent any further contaminants being introduced. By designating a high-risk, unpackaged area and a low risk packaged area, X-ray can act as a gatekeeper to only allow compliant products through. Even in whole birds, metal contaminants on the scale of a single millimeter can be detected and removed from the product flow.
For products expected to be bone-free, however, the inspection philosophy becomes more complex. Inspection at the end, in a sealed container, is beneficial as it ensures no new contaminants can be introduced. However, if value has been added, then it might not be possible to rework rejected product. Instead it is preferable to detect bone much earlier in the process, ideally while it is still whole muscle. The natural variation between birds, and the automated preparation of chicken breasts, means the resulting muscle is not uniform. The varying thickness and uneven presentation can make it difficult to detect bones which are low density and hollow. The growth of dual-energy X-ray has sought to resolve some of these issues.
Dual-energy systems generate two images — one produced by high-energy X-rays and the other from low-energy X-rays. Because bone and muscle are made from different atomic constituents, they respond differently to the two energies. This allows the system to differentiate between variation in thickness and the presence of bone — leading to more sensitive detection. A well set-up system can detect wishbones of a few millimeters in length or rib and fan bones of around 5 mm. Having identified any bones left in the product, the items can be reworked easily to minimize product wastage.
If the product is to be sold as whole breasts, these items can then be packaged and move from a high-risk to a low-risk area, via a second X-ray system to confirm the absence of metal, glass or other contaminants in the sealed product.
For processed products, the muscle is often passed through a pipeline. This offers an excellent opportunity for X-ray inspection. Rather than using dual energy to compensate for the variation in product thickness, the predictable cross-section of the pipeline can be used to give a uniform inspection. This uniform presentation allows for excellent sensitivity against bone — even wishbones a few millimeters in length — and sub-millimeter sensitivity to metal contaminants. Additionally, the rejected product can be diverted into a mechanical separator, removing the bone fragment but preserving the protein — ensuring there is minimal waste.
If the product has passed through a grinder, the X-ray system can be configured to ignore bones below a certain size while still rejecting larger bones. This can provide useful feedback for whether the grinder is operating as expected.
Further in the process, this material may be formed into nuggets or other shapes. Wide-format X-ray inspection lends itself to positioning directly after the former — or after the freezer — where the product is singulated and separated. Belt widths of 1 meter are common, requiring specialist X-ray equipment.
However, inspection at this stage can verify individual item shape and mass — ensuring every nugget is exactly 12g — and check there has been clean removal from the mold; all while allowing for the detection of sub-millimeter metal contaminants, as well as glass and bone fragments. A multilane reject or air curtain allows for the removal of a single item. Contrast this with inspection once bagged, where a single reject results in the removal of dozens of items.
As with unprocessed products, a final inspection after packaging is also valuable. Inspecting a sealed product should always be the last step in any manufacturing process. This final step also provides the opportunity to gain a final count of the number of items leaving the production. Unlike other foreign object detection systems, X-ray provides a product count. By comparing the product count at each step along the process, it is possible to determine where in the process losses are occurring. Batch reporting and other KPI data can be made available to ensure uptime, detection performance and production rates are meeting targets.
X-ray inspection can provide more than just improved metal contaminant detection. Bone detection is of particular interest for poultry inspection — but choosing where to inspect in the process is just as important as choosing what equipment to use. Balancing performance and quality assurance with capital costs and maximizing the ability to rework rejected material is a key decision and expert advice on specific requirements is critical to ensure implementation meets your targets.
David Bosworth is a senior program manager at Cambridgeshire X-ray equipment specialist Cheyney Design. As well as working with customers to determine how best to solve their needs, he heads up the company's North American operations. David has a PhD in material science from the University of Cambridge.
