A recent Produce Processing article reported that for year-to-date through Aug. 30, frozen fruit and vegetables increased the most among produce sales, up 26.8% year-to-date (fresh produce department sales are up 10.9% over the same time period in 2019).
That’s good news for the frozen food companies, but while they ramp up operations to meet demand, they must also continue to be vigilant in their food safety inspection practices. One frozen corn provider wanted to ensure they provided a consistent quality product to the customer, so they evaluated the latest inspection technology for food metal detectors.
Most food manufacturers utilize food weighing and inspection equipment as part of their food safety program. Metal detection technology is one of the most common ways that food processers help ensure there are no metal contaminants in the foods that reach the customers’ hands. These contaminants could have originated in products coming from a supplier, or they could have fallen into the processing stream by way of broken or worn equipment or by nuts, bolts, and screws that have loosened from quickly moving, vibrating machinery.
Food metal detectors help find small particles of metal by utilizing coils wound on a nonmetallic frame and connected to a high-frequency radio transmitter. When a particle of metal passes through the aperture, the electromagnetic field is disturbed under one coil, changing the output signal by a few microvolts. This output indicates metal is present, so the product can be kicked off the line and the appropriate personnel can be alerted.
It sounds pretty simple, but things get a bit complicated with frozen foods, which have high “product effect.” Product effect occurs when a product has a conductive property which affects the magnetic field generated by the food metal detector. This is typically found in high-salt and high-moisture products.
For example, partially-frozen packaged vegetables tend to have a high product effect. This negatively impacts the metal detector’s ability to distinguish between actual non-ferrous metal contaminants and the false signal given by the combination of typical product attributes. Complicating matters even more, upstream machinery can accumulate ice which may occasionally deposit into the product — like at the beginning of a new batch. This is also a challenge for metal detectors because the ice deposit can “look” like a metal contaminant to the metal detector.
One frozen food company was aware of these difficulties, so they tested one of the latest metal detection technologies, Multiscan, to see if it could overcome the product effect challenges.
With Multiscan technology, the operator picks a set of up to five frequencies from 50 kHz to 1000 kHz. The equipment scans through each frequency, effectively acting like five metal detectors in one. As a result, the detectors can run a frequency close to ideal for most any type of metal encountered. The probability of detection is greatly increased and escapes essentially disappear. Sensitivity is optimized because a different frequency can target each type of metal of concern.
The benefit was evident after a product test. The company sent us a 20-lb case of frozen corn (20F) to be tested using Multiscan metal detection technology.
Five different frequencies were utilized (300, 450, 575, 725, 900) to configure the metal detector before ferrous, nonferrous, and stainless steel test spheres were inserted into the product in multiple locations; leading, trailing, and middle of the container, to simulate the unpredictability of contaminant location in real production. The results revealed that ferrous metal was best detected at 300 kHz, while nonferrous and stainless steel metals were best detected at 725 kHz, and 900 kHz respectively. Alloys of metals have different reactions too. And the shape, orientation and position of the metal can change the resulting signals in a metal detector and warrant different frequencies for optimal detection. With Multiscan technology, unique metal contaminants can be detected at different locations in the package with different frequencies.
Test results were positive.
Product inspection equipment that utilizes Multiscan metal detection technology can help provide frozen food companies with the performance they need to detect foreign metal objects in food and improve the quality and safety of its products. This type of equipment protects a company’s brand, as the last thing a food producer wants to experience is an ‘ear-full’ of complaints from customers who find metal in their frozen corn.