Why is Broccoli So Difficult? Especially When It's Frozen.

The trade publication, Food Engineering, recently published an article addressing the issue of finding hidden metal among frozen vegetables. A bulk food processor and supplier that flash freezes its fresh-picked broccoli and other vegetables discovered it needed to “upgrade its metal detection technology to identify increasingly smaller metal foreign objects as a result of more stringent requirements from customers.”

Industrial food metal detectors are used in the food production line to find metal slivers, needles, broken metal parts and wires that could enter the processing stream. This task is especially difficult with conventional inspection practices because of their variable size, thin shape, material composition, numerous possible orientations in a package and their light density.

To make matters worse, high-moisture products that are complicated by air bubbles and differing densities, can negatively impact a metal detector’s ability to distinguish between actual non-ferrous metal contaminants and the false signal given by a combination of typical product attributes. All metals, whether iron, stainless steel, brass or aluminum, react differently to an electromagnetic field, which is the principal underlying metal detection in products. These reactions change based on shape, size, orientation and position.

The inspection process of frozen foods is further complicated by the varying densities, the possible air bubbles and other physical characteristics of each product, since no two are exactly the same. If the freezer isn’t efficient or the products start to thaw, its unfrozen center could then contain moisture, which can create a strong product specific signal that may mask detection of smaller signals generated by a contaminant.

Let’s complicate these food safety matters even further with the presence of loud running machinery, motors turning off and on, vibrating equipment, and other plant noise — which all can impact the performance of standard metal detector technology. Typical metal detection equipment needs to have a “quiet” background so it can focus on finding the metal signal. Engineers call this the signal-to-noise ratio. The bigger the better.

Don’t despair, though, as there is a solution. The best way to overcome the wet product effect and the noise challenge is to use additional frequencies. Multiscan, multi-frequency, industrial food metal detectors can provide the highest probability of finding ferrous, non-ferrous, and stainless steel metal contaminants.

Food metal detectors that are equipped with Multiscan, multi-frequency, technology enable operators to pick a set of up to five frequencies, from 50 kHz to 1000 kHz. The technology then scans through each frequency at a very rapid rate. Running five frequencies helps make the machine close to ideal for detecting any type of metal you might encounter. Sensitivity is optimized, as you can choose to run the optimal frequency for each type of metal of concern. The result is that the probability of detection goes up exponentially and escapes are reduced.

The food processor named in the article upgraded its metal detector to multiscan technology and found that product effect was reduced and the interference of noise during processing became controlled, which helped optimize their inspection process, and resulted in recovery of an additional 5-10% of their product. The company is even more confident that its products are free from metal contaminants, which protects the customers and the brand.

So the next time a parent tells their child to eat their vegetables because they are good for them, folks can have a high degree of confidence there’s nothing bad in them as well.

Editor’s Note: Do you wonder if you have the right food product inspection equipment in place to keep consumers safe and protect your brand? To find out how they work and which one will work best for you, read A Practical Guide to Metal Detection and X-ray Inspection of Food.