Gravity metal detector chosen for bulk nuts and seeds

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The company first acquired a Stealth Gravity metal detector for its products in 2013. “We installed a further line, and wanted to obtain the same level of reliability and accuracy,” said David Danil, managing director at Levantine. 

“We are BRC (British Retail Consortium) certified and, as a part of that, we have HACCP (Hazard Analysis and Critical Control Point) assessments, with metal contaminant detection high up on the list of control points. Sensitivity levels are also hugely important, and the Fortress equipment exceeded those requirements too.” 

While different varieties of nut still account for the majority of Levantine’s volume, seeds are becoming an increasingly important part of the business. 

The company caters for retail portion packs, including own-label products for many of the major multiples. Yet, the majority of its business involves the bulk supply of nuts and seeds to other food processors, including snack brands, chocolatiers and ice cream manufacturers. Bulk bags are filled in weights of 12.5kg, 15kg, 25kg and even 1 tonne. 

A key question for Levantine was the speed and precision of the reject system, which is clearly a critical issue with valuable free-flowing product in freefall. It is vital that any contaminant is accurately targeted and removed, but this needs to happen without removing excessive amounts of uncontaminated product with it. 

“In terms of the reject mechanism, we knew that this system did the job for us,” said Danil. “The speed is adjustable via a pressure-reducing valve, depending on the weight and speed of the product.” 

One concern before installation was that vibration in such a busy manufacturing environment, with product pouring vertically through the aperture, might adversely affect the accuracy of the machine. “The fixing needs to be solid, since anything that shakes the metal detector affects the reading and its accuracy,” said Danil. 

The reject mechanism, in particular, is powerful and precise, so the metal detector needs to be securely held in place to avoid physical interference. But it also needs to be effectively isolated to avoid electrical interference.

The need to factor in ‘product effect’ is important in many food categories, including nuts and seeds, especially where salt, oils and other seasonings can mimic the presence of metal contaminants. “The impact of this ‘wet’ product effect has been minimal for us,” concluded Danil. “The machine settings can be adjusted to read the product accurately. Typically, we are only likely to get a false reject where there is a clump of product, salt or herbs, for example. It’s not a big issue for us.” 

To save on space on the factory floor, the metal detector is located midway between the first floor of the factory and a mezzanine. It is controlled from a remote panel at operator level, with product falling from a hopper to the weighing and bagging station below. 

The solution is said to offer high sensitivity which comes with Digital Signal Processing technology, allowing the detection of ferrous, non-ferrous and stainless steel contaminants, even down to the smallest dimensions. Data collection is integral to the system, with Contact Reporter Software helping to ensure HACCP compliance.