Top Technologies for Foreign Object Control

The detection capability of both systems is limited by the so-called “product effect,” which can cause false positives or negatives. “In metal detectors, product effect is the phenomenon whereby the product and the contaminant generate a similar signal at the same frequency,” says Mike Munnelly, marketing manager of life sciences manufacturing at Thermo Fisher Scientific in Waltham, Mass.

The main cause of this product effect is the conductivity of the food, which can be increased by even the smallest variations in salt content, moisture, and temperature. Complex food matrixes make product effect even worse.

The most advanced metal detectors minimize the problem by using up to five frequencies at once. “Different metals respond better to different frequencies,” says Munnelly. With multiple frequencies, we can offer optimal performance. With just one, there is always some compromise to be made, maybe reducing the sensitivity to a particular metal in order to avoid product effect.”

Complex matrixes are a problem for X-rays too, due to their density profile. “With meat skewers, for example, detecting light contaminants would be much more difficult, as the wooden stick, the meat, and the vegetable oil would have different densities,” says Alex Kinne, an applications engineer at Thermo Fisher Scientific.

One solution is scanning products from different angles. “Using multiple beams greatly improves the chances of finding the most difficult contaminants, like glass inside of glass jars, that can hide at the bottom or in corners or edges,” says Kinne.

Another area of improvement for X-rays is imaging software that can differentiate between subtle changes in darkness: “It’s quite a difficult software to do well, but it has become more advanced over time, improving the probability of detecting contaminants,” says Munnelly.

Making Technologies Work Together

In general, each of these technologies has its own natural place in the production line: Sorting, filtering, and magnets only work with produce, liquids, or dry powders. Metal detectors and X-rays are better suited for constituted products. Their placement, however, is rather flexible.

“X-ray and metal detectors are used at different critical control points rather than in tandem,” says Kinne. “For example, in meat processing, metal detection may be used to inspect large oblong pieces of raw meat, and then X-ray after food is packaged.”

How you combine systems really depends on your risk, your food matrix, your line speed, and the capabilities of available technologies, says Davis.

For Munnelly, using X-ray, metal detection, or a combination of both depends on how “safe” food manufacturers want to be. “They could be guided by brand protection, a particular local regulation, or the request of a customer to use one or both of them,” he adds.

Investigating Foreign Object Findings

When a foreign object incident occurs, there are a few questions to answer as quickly as possible: What is it? Where does it come from? Why did it end up there? How much product could potentially be contaminated?

Investigation always starts in the facility, but it doesn’t necessarily end there. In some cases, food companies will resort to a lab to continue it with more sophisticated technology. “Whether or not a lab is involved depends on the impact of the incident,” says David Wright, associate principal scientist at Reading Scientific Services Ltd. (RSSL) in the United Kingdom. “If [a contamination] has gained media or regulatory attention, they’re likely going to investigate. When that’s not the case, then investigation is still advisable, as it allows the prevention of future, and potentially more serious, contamination.”

One risk of not conducting a deep analysis is misidentifying the material completely. “We had a case where a piece of suspected glass came in, which turned out to be an extremely hard plastic type. This might be unusual, but just highlights the fact that you might see something that it really isn’t,” says Rene Friedrichs, RSSL’s microscopy lab manager.