Single vs Dual Energy X-ray Technology for Food Inspection – 4 Factors to Help You Decide

Food & Beverage
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Food processors have relied on x-ray technology since the early 1990s to safeguard their brands and protect customers. Both single and dual energy x-ray technology are used for foreign body contamination detection today, with some manufacturers believing that, regardless of the application, dual energy is always best. However, this is a myth; dual energy doesn’t automatically give better inspection results.

This article explains that both technologies have their place and that the correct choice of energy depends on four factors: the likely contaminants and product, packaging, production speed and customer specifications.

1. Likely Contaminants and Product

Before selecting a technology, it’s important to consider the type of product and the likely contaminants. For example, in whole potatoes, the most likely contaminants are stone or a piece of golf ball, whereas in cookies or ready-to-eat foods, the most common contaminants are small metal and glass.

Single energy x-ray technology gives exceptional levels of detection for stainless steel, ferrous metals and non-ferrous metals. It’s also extremely effective at detecting glass, calcified bone, mineral stone and high-density plastics and rubber in products that are homogeneous in texture such as butter or yogurt. However, single energy is unable to detect thin glass, stones, rocks and low-density plastics and rubber in heterogeneous products such as a bag of hard candies.

In contrast, dual energy x-ray technology offers a clear advantage when detecting inorganic foreign bodies such as flat glass (as opposed to cylindrical glass), bone, stones, rocks and some low-density rubber and plastics. An inorganic foreign body in a heterogeneous product is also more detectable using dual energy x-ray technology. For example, dual energy makes it possible to detect flat glass and stone in mixed nuts, which can be challenging to detect using single energy detectors. Read this application note for unpackaged walnuts.

Single energy x-ray technology provides safety and quality assurance at every stage of the production process for raw, bulk, pumped and packaged applications. However, identifying foreign bodies in products with many density levels can prove more difficult for single energy detectors as the varying densities create ‘busy’ x-ray images. For example, the density variance caused by overlapping stems and leaves in bags of mixed salad leaves makes it difficult for single energy technology to identify contaminants. Download an example on how x-ray technology helps packaged salad bags manufacturers to ensure total quality and safety of their foods.

In contrast, dual energy x-ray technology lends itself to inspecting ‘difficult’ or ‘busy’ x-ray images caused by products with high variations in density due to its ability to discriminate materials by their chemical composition. It’s therefore capable of detecting flat glass and stone in multi-textured foods, such as trail mix, cereal and confectionery, something which single energy technology would find more challenging. Furthermore, dual energy is also capable of detecting rocks, golf balls and rubber grommets in potatoes.

2. Packaging

After considering the product and likely contaminants, it’s important to focus on the type of packaging material and whether or not the product will be inspected on its own or as part of a multipack.

Glass jars and bottles are one of the most difficult types of packaging to inspect. This is mainly because the primary contaminant is glass, the same material as the packaging. What’s more, metal cans and glass jars can also be challenging to inspect as parts of the containers will always be present in the inspected image. Single energy technology is ideal for inspecting a glass jar of jelly where the likely contaminant is glass, and modern special adaptive masking and inspection routines offer unsurpassed detection by dynamically adjusting to each individual pack. Read here the case study of Rodolfi Mansueto, an Italian manufacturer of tomato sauces in glass jars, and how by installing single energy x-ray technology in their lines they prevent glass contamination in their final products.

Single energy x-ray technology is also capable of inspecting unpackaged foods, as well as products in a variety of other packaging types such as metal and ceramic containers, plastic containers, cartons/boxes, pouches, bags/sacks, trays and tubes. 

Dual energy x-ray technology is able to detect inorganic contaminants in a variety of packaged products, and lends itself to finding foreign bodies in innovative packaging designs, such as fold-out cardboard sandwich packaging and corrugated card encasements, that can prove troublesome for traditional inspection tools. In addition, dual energy detectors are ideal for inspecting multipacks such as a multipack case of chips. This is because the dual energy essentially removes the edges of the individual packages within the case, making it easier to see contaminants that could potentially be hiding inside the box. 

Glass Detection in Chocolates
Rubber Detection in Salad Packages
Dual Energy Meat Inspection for Short Ribs
Stone Detection in Leafy Greens

3. Production Speed

As a rule of thumb, high-speed applications such as metal cans and flow-wrapped products like energy bars tend to be more suited to single energy x-ray inspection. Single energy x-ray technology is ideal for most packaging lines with products travelling at speeds between 150 and 400 feet per minute (FPM). In contrast, dual energy technology is better at inspecting incoming raw materials/ingredients such as nuts, which typically tend to be slower applications, travelling at speeds of between 80 and 200 FPM.

4. Customer Specifications

Customers’ requirements also determine the x-ray energy choice. For example, retail stores may specify that their suppliers have inspection technology that’s capable of detecting contaminants as small as .4 mm, which can easily be achieved with many applications using single energy x-ray technology.  This is because products will have been processed which increases the risk of small contaminants, in particular metal.

Alternatively, a processor may stipulate that a grower or farmer has the capacity to detect 3 mm tramp metal or rock/stone, which can be easily achieved using dual energy technology. Field contaminants are the only likely contaminants this far up the processing stream as the fresh crops won’t yet have been processed. Read here how Higos El Pajarero, Spanish leading manufacturer of dried figs, implemented an Eagle™ Bulk 415 PRO with MDX technology to enhance the quality of their fruit and comply with their customer specifications.

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