Potatoes are one of the world’s most versatile, main food crops. Demand never drops, with fries, crisps and table potatoes a household staple. To keep them free of metal contaminants Fortress Technology has designed an industrial-sized Bulk Potato Slider Detector System. Helping farmers to safeguard their reputations and livelihoods. 

Harvesting 5.31 million tons of potatoes annually, and with an annual UK farm gate value worth GBP 703 million, ensuring crops are free of metal contaminants is essential to any thriving farm. In the last decade, a number of crop processors, as an added safety precaution, have installed bulk metal detection systems after washing farmed produce and before packing into sacks. Further enhancing quality control at every phase of the food manufacturing supply chain.

Introducing this level of scrutiny is not unfounded. In October 2014, potato processors suffered a serious industry blow – product tampering. The discovery of needles in potatoes for one large international farmer resulted in a nationwide recall of nearly one million pounds of produce.

Although no sharp metal objects were detected in produce farmed by Fortress customers, one major potato processor took proactive steps to reassure their extensive supplier base and prevent an incident of this magnitude occurring. Their investment in three robust industrial-sized Fortress metal detectors continues to inspect 140,000 pounds of potatoes hourly.


Without upstream inspection, a potato containing a needle could unknowingly be thinly sliced into crisps. The subsequent metal fragments may be too small for even the most sensitive downstream metal inspection systems to detect. For a market that’s worth over £2 billion annually[ii], crisp producers are naturally eager to ensure their suppliers have robust inspection systems in place to help eliminate contaminants in root vegetables before processing.

As well as needles, drink cans casually discarded in crop fields, machinery nuts and bolts, or wire fencing blown down in a storm, can all be turned into the smallest metal fragments by powerful harvesters, cautions Fortress European managing director Phil Brown. These can easily disperse and embed contaminants into crops.

Addressing these fears directly, the prominent crop processor swiftly installed three industrial-sized Fortress Bulk Potato Slider Detector Systems. To this day, they continue to play an important role in guaranteeing high standards across the potato supply chain and provide valuable assurance to major retailers.


When creating the robust design, Fortress was mindful that potatoes have a number of product attributes that could affect the accuracy of the metal detectors. Phil elaborates: “Potatoes are typically washed and wet. They are neither super clean or dry, and they come in all different sizes.” These factors can impact a metal detector’s ability to distinguish between the potatoes and any metal contaminants introduced, leading to false signals and consequently wasted produce.

To ensure the potatoes were run at the highest performance level, Fortress engineered a special VLF (very low frequency) coil. This allows all potatoes to appear as dry products on the machine, essentially ignoring the product effect caused by soil, grit and moisture.

Another essential feature designed for harsh, rigorous production environments is the BSH rugged casing. This helps to provide better stability and metal detector performance for when rolling potatoes collide with the sides of the system as they are funnelled down the conveyor.


Orientation effect, especially when trying to detect long, thin needles, was another added challenge Fortress resolved. Typically, these contaminants will be embedded within the potato or root vegetable. Detecting any fragments will depend entirely on the direction that a bouncing potato is passing through the metal detector. In one orientation, the signal for the needle may be huge. But if turned 90 degrees, the needle may pass through the metal detector’s electromagnetic field undetected with little to no disturbance.

To combat this, Fortress engineered the metal detector with a rolling-system rather than traditional belt. It provides a stronger signal than stagnant objects. “The potatoes roll through the metal detector to limit the chance that a needle misses detection due to orientation effect,” expands Phil. The technique worked remarkably well in all test cases, with the customised metal detection unit reporting minimal false positives and superior accuracy and metal detection sensitivity.

Warehouse floorspace and how the reject system could align with other design features were also carefully addressed. Phil clarifies: “Space on farms is often tight. Products also roll through at fast speeds, making it challenging to account for the placement of potatoes as they pass through the metal detectors. The benefit of our roll-through design is there is no belt. Instead, a flap expels contaminated product to the reject area below.”

A simple conveyor with a low-maintenance UHMW slider bed was integrated alongside the farmers existing cleaning and grading systems, resulting in an optimised and cost-effective solution.


It is increasingly clear that the task of contamination control is no longer reserved for food processors; it stretches right up the supply chain. With the focus shifting from analysing hazards to preventing them, contaminant detection from farm right through to fork is essential to securing new business deals and guaranteeing the delivery of consumer-safe products.

Safety in the fast-evolving food sector places heavy emphasis on shared responsibility, notes Phil.  Upstream inspection after harvesting and before processing is now widely regarded as best practice.

Globally, farmers face multiple challenges every year, from floods and droughts to poor harvests, fluctuating energy costs and crop damage. “Although product tampering is extremely rare, in the last decade Fortress has observed a large uplift in enquiries from root vegetable and potato farmers and bulk processors for robust gravity and conveyor metal detection systems. These can help to prevent future adulteration and contamination events from causing potentially catastrophic damage to brand reputations,” ends Phil.


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