Smart piece of detection

Most snack producers opt for gravity metal detectors. With 15 Fortress mini Vertex snack inspection systems integrated with multi-head weighers in its Aintree factory, Trigon Snacks is no exception. Yet, for its latest coated honey roast nut production line, the nut specialist selected a bespoke linear Stealth metal detector with an innovative retractable conveyor reject system.

Processing 7,000 tons of nuts annually from its British Retail Consortium A-grade and RSPO certified facility, Trigon Snacks supplies a wide range of nuts and snacks to the licensed trade, retailers and food service operators. Marketed under its own Big D and Bar Bite brands, as well as retailer own-labels, for its new honey roasted nuts line the company commissioned a highly sensitive horizontal metal detection concept.

Sensitivity and tolerance

Stringent retailer COPs specified that as ‘naked nuts’ the new honey-coated range must be inspected for metal contaminants prior to own-label packaging. Additionally, Trigon required a supermarket spec metal detector that was sensitive enough to adapt to the fine oil and sugar tolerances.

For logistical reasons, a small-footprint, wide-head Stealth metal detector engineered to inspect the fried, dried and seasoned nuts on a conveyor before entering the chute and falling into the one-ton sacks (over 1,000 kilograms), was the most viable and accessible option. 

Screening 32 tons of honey roasted nuts daily, space limitations was a key driver to the design, reaffirms Trigon’s lead engineer Mark Grieve. “Being located on a mezzanine floor, we commissioned a wide head yet highly sensitive metal detector with a specially adapted linear conveyor system measuring just 40 cm wide.”

Reject on a roller

Factoring in the conveying and reject system was critical to guarantee reliable operation and avoid false readings. Given the tight footprint, a customised solution was the best way to ensure that metal detector performance was not compromised.

The low-profile nuts, combined with the inspection speed, meant that a kicker would be incompatible. It is also virtually impossible to isolate and divert contaminated products with naked products. With insufficient space to accommodate a flap style reject, Fortress instead engineered a clever and efficient retracting band conveyor and reject mechanism.

Rather than a typical tongue and groove conveyor, the rollers on Trigon’s moveable easy-clean, food-grade belt are rounded. The metal detector which sits at the front of the conveyor calculates precisely how long the contaminated nuts will take to reach the end of the conveyor band, communicating via the metal detector control system. The belt then smoothly retracts back on a sliding rail, rolling the rejected nuts into the dedicated bin located beneath the conveyor, resuming its inspection position in just seconds. 

To-date, Trigon reports zero false rejects on the honey roasted nut line, upholding the company’s longstanding sustainable, ethical and traceable principles. Despite admitting he was slightly apprehensive by the compact dimensions of the entire system, Mark corroborates that it has already proved itself to be a reliable and easy-to-use machine.

Hourly manual tests are the only reported source of daily waste. The lead engineer estimates this to be less than 0.05% of the total production, well below the food manufacturing average, which on some lines can reach double figures.

Smashing all expectations

From a sensitivity perspective, Fortress sales manager Jaison Anand validates that the metal detector is smashing expectations. Capable of detecting ferrous and non-ferrous particles as small as 1.0mm and stainless steel particles down to 1.5mm, he attributes this level of sensitivity to the aperture dimensions. “Aperture size is critical to optimal operation. If aligned to the size of the product being inspected, it delivers the best performance. That’s why we installed a wide, yet low-profile, metal detector head on the Trigon honey nut line.”

A long-standing advocate of Fortress equipment, Trigon Snacks, which last year celebrated its half century milestone, was in fact one of the food safety specialist’s first UK snack customers.

Managing director Phil Brown, a sales manager at the time, recollects the moment Trigon became the springboard for the development of Fortress Technology’s mini Vertex metal detector that’s now adopted widely by snack manufacturers across the globe. “I’d showcased a standard-sized gravity metal detector, but they needed something much more compact, with ultra slim case dimensions to slot between the volumetric filler and bagging machine. We created something very bespoke, taking a ‘try it and see if you like it’ approach. As we fully anticipated, they did!”

Several decades on and 15 of these very Vertex metal detectors continue to comply with HACCP regulations, detecting the tiniest metal particles and protecting the Trigon own-label and retailer brands.