Getting Metal Out of Chocolate

A Guide to the Best Locations for Magnetic Separators and Metal Detectors in a Chocolate Production Line

Chocolate is made from the exceptionally hard cocoa bean and this means that metal gets introduced into the process, especially from equipment wear.  There have been a number of food safety alerts due to metal contamination in chocolate including the Raw Chocolate Company recalling chocolate goji berries because they may contain small pieces of metal.

However, a series of carefully selected and placed Metal Detectors and Magnetic Separators will remove any metal from the process before it becomes a bar that is loved by millions.

Magnetic Separator Location in a Chocolate Production Line
The locations for Magnetic Separators in a chocolate production process line

The Stages of Metal Removal

Stage 1 – When the cocoa beans are discharged from the delivery vessel, metal is removed by passing all the beans through a heavy duty Grate Magnet.  This captures any larger ferrous metal, like nails, nuts and bolts.

Stage 2 – After the cocoa beans have been cleaned and roasted, they are cracked with the shells being discarded and the nuts being fed into the process.  After cracking, the nuts can be fed on a conveyor through a Metal Detector (Metron C) before passing onto the grinder.  This protects the grinder from being damaged by metal freed in the cracking process.

Stage 3 – After the grinder, the nuts have been converted into a chocolate liquor.  The process of grinding will introduce fine metal into the process and this is removed with a Magnetic Liquid Trap followed by a P-Tron Metal Detector.

Liquid Chocolate Magnetic Trap
A Bunting Magnetic Liquid Trap with a Waterjacket

Stage 4 – The chocolate liquor passes through a hydraulic press where it is split into cocoa butter and cake for cocoa powder.  The cocoa cake is fed onto a grinder and screen with the packaged cocoa powder being passed through a Metal Detector Metron C on a conveyor as a final check.

Stage 5 – The cocoa butter is fed onto a mixer where sugar, milk and flavouring is added.  After mixing and passing through a series of rollers, the mixture is emulsified before being heated.  This molten hot mix is then passed through a Magnetic Liquid Trap with a waterjacket (the hot water in the waterjacket stops any material from cooling).   Care has to be taken in selecting the right magnets as high temperatures can irreversibly damage the magnetic field.  The magnets must be suitable for use in high temperature environments.  After the Magnetic Liquid Trap, the mixture is passed through a P-Tron Metal Detector to detect any non-ferrous metal that may still be present.  This joint protection is important to prevent damage to the next stage of the process (the moulds).

Stage 6 – After the chocolate is fed into moulds it is then cooled.  The final check is after cooling, when the moulded and formed chocolate is then fed on a conveyor through a Metal Detector (Metron C).  The metal-free chocolate is then packaging and despatched for sale to the millions of chocolate lovers all over the world.

Multi-stage Metal Detection and Magnetic Separation may appear excessive, but the best way to remove all metal from the process is to focus on areas where metal may be introduced or released as part of the production process.

For further information on ‘Getting Metal Out’ of Chocolate or any foodstuffs, please contact us on:

Phone: +44 (0) 1442 875081

Other Food Safety Articles



The Misconception of Eddy Current Rotor Speed

1st of 5 Misconceptions About Eddy Current Separation

Eddy Current Separators are used extensively throughout the recycling industry to separate non-ferrous metal (e.g. aluminium beverage cans, shredded aluminium and copper etc) from non-metallic materials.  One of the first Eddy Current Separators was built by the Bird Group in the UK in 1981 and the separation system has now become common place in recycling operations across the world.  But there are still some misconceptions about eddy current separation.

The magnetic rotor needs to rotate as fast as possible.

An Eddy Current Separator consists of a Magnetic Rotor with alternating magnetic poles rotating inside a slower rotating non-metallic shell.  Eddy Currents are induced into a non-ferrous metal particle when exposed to the changing magnetic polarity.  The eddy currents cause an electric current to be generated in the non-ferrous metal particle that produces its own magnetic field.  This magnetic field reacts with the rotating magnetic field of the rotor, resulting in a repulsive effect that throws the non-ferrous metal away from the rotating magnetic field.


It would be fair to assume that increasing the number of polarity changes in one second would have an effect on the separation.  In practice, the actual amount that a non-ferrous metal particle is thrown reaches a peak and as the rotor speed increases then separation actually deteriorates.

To inject the maximum amount of repulsive energy into a non-ferrous metal particle there needs to be a dwell time when the two opposing fields meet and if this is too short then the injected energy is less.  It is considered that very high rotation speeds do not allow for sufficient dwell time.  Nevertheless, manufacturers commonly claim that Eddy Currents with the highest rotating speed are the best designs.

In reality, the optimum separation speed will be unique to each design of Eddy Current Magnetic Rotor, but is commonly between 2,600 and 5,000 RPM.

Also, there are other considerations such as maintenance and wear.  As the rotor speed increases there is a higher wear factor on key components such as bearings.  Then the question has be asked that if one more item of metal is recovered by a Magnetic Rotor spinning at 5,000 RPM than one operating at 3,000 RPM but the resultant bearing wear is high, is it better to run at the lower speed.

Bunting will be exhibiting at Waste 16 on 9th June 2016 and RWM at the NEC in Birmingham (13th – 15th September 2016) and will be available to discuss the technology and physics behind eddy current separation.

For further details on the Bunting range of Eddy Current Separators, Magnetic Separators and Metal Detectors please contact Carlton Hicks ( or our technical sales team on:



Bunting Exhibiting at Waste 16

This year, Bunting Europe is a headline sponsor of the WASTE ’16 exhibition (Thursday 9th June 2016 AJ Bell Stadium, Salford, Manchester, UK) and will be on stand A79.  Now in its third year, WASTE ‘16, the Waste and Skip Trade Exhibition, is the North’s premier waste management event.

A key aspect of successfully managing waste is to recover and then sell valuable materials.  Metals are one of the most important and valuable materials in a waste stream and can be recovered using different designs of Magnetic Separator.

At WASTE ’16, we will be on hand to discuss ways to improve the recovery of metal and the purity including:Bunting HISC Stainless Steel Separator-2

On stand A79, we will also be available to discuss our latest new installation of a complete Metal Separation System (including a Vibratory Feeder, Magnetic Drum, Eddy Current Separator and Metal Separator) at a plastics recycling operation in Kent.

We look forward to seeing you at the WASTE ’16!

For further information on metal separation and recovery, please contact us on:

Phone: +44 (0) 1442 875081
Fax: +44 (0) 1442 875009


Is UK Manufacturing Really in Recession?

The BBC has reported that UK manufacturing has returned to recession for the 3rd time in 8 years.  This frightening statistic illustrates the challenges facing the manufacturing industry in the UK, with manufacturing output for the first quarter of 2016 being 1.9% lower than the same quarter in 2015.

However, there is some positive news, with PRW reporting that production of rubber and plastic products did show strong signs of recovery, increasing by 1.6%.  For us, this is good news as we supply equipment such as Magnetic Separators and Metal Detectors to remove metal from the plastics process and we have seen a general increase in activity in that sector.

Bunting Drawer Magnet


Manufacturing provides the cornerstone for any economy and the uncertainty surrounding the future existence of steel production in the UK continues to dominate the news.  However, that uncertainty is not only related to steel production, with the UK’s referendum on EU membership gathering pace as we approach 23rd June.  The predicted outcome of whether the UK will or will not remain in the EU is very much in the balance.

As a UK manufacturer of Magnetic Separators and Magnets, we are very aware of the challenges.  Many of our customers are, themselves, manufacturers.  We have broadened our sights and worked hard this year to develop business overseas with new distributors and representatives.  The effect on our overseas business after the referendum is an unwelcome unknown and this is an uncertainty that doesn’t help when setting marketing and business strategies for the future.

These are challenging times for the UK’s manufacturing sector.

Export Order for 12 Custom Plate Magnets

Removing Metal From Shredded Tobacco

Bunting Magnetics Europe Ltd has designed, manufactured and shipped 12 large and custom designed Self-Clean Plate Magnets to a customer in Italy for an export project in Indonesia.  The export order was valued at over £50,000 and was the result of close cooperation between the Bunting Europe engineering team based in Berkhamsted in the UK and the Italian customers engineers.

Bunting Magnetics Plate Magnets-0959

Plate Magnets are a simple form of Magnetic Separator with blocks of magnets magnetically arranged inside a rugged stainless steel fabricated housing to project a magnetic field on the flat surface of the plate.  The projected magnetic field captures both fine ferrous contamination and larger pieces of tramp ferrous metal from various types of free flowing material (including powdery, moist, lumpy, and abrasive products through to large material that might choke, bridge, or cause rapid wear in Magnetic Cartridge or Tube based separators).

For the Italian project, the objective was to remove tramp ferrous metal contamination from tobacco to protect damage to delicate and expensive cutter blades.  The product flow was poor with a high moisture content and so a Plate Magnet was the best suited design of Magnetic Separator for the application.  Due to specific application requirements, the Plate Magnet was custom designed to produce a specific shape and intensity of magnetic field.  Each Plate Magnet had a face of 600mm by 130mm with a depth of 45mm and weighed approx. 50kgs.  These were the largest Plate Magnets manufactured in the UK by Bunting.  The custom design, using high-energy rare earth magnets, meant that a peak magnetic field of over 10,000 gauss was produced on the surface, which was flat as recommended for low density product flows, inverted installations and sanitary applications.

The Plate Magnets were positioned inside chutes and due to the size and weight of each unit, the customer required each one to be self-cleaning, whereby any captured metal would be automatically removed and discarded.  The self-cleaning design requires a counter plate to be placed against the surface of the Plate Magnet.  During the self-cleaning process, both the counter plate and the main body of the Plate Magnet is pulled away from the chute then the counter plate is pulled away from the main body.  Any magnetically entrapped material is held against the counter plate and becomes demagnetized as the Plate Magnet moves away allowing the ferrous material to falls away into a discharge collection area.

The 12 identical Plate Magnets were designed, manufactured and despatched within 9 weeks.  The size, weight and magnetic strength of each Plate Magnet dictated that each unit had to be packed separately for shipment to Italy.

Dave Hill, Bunting’s Head of Sales, explained how Bunting secured the order.  “Being flexible and having the engineering capabilities in Europe to custom design the Plate Magnet for the client was vitally important.  Ultimately, that was the deciding factor.”

Plate Magnets are a very versatile and easy Magnetic Separators to install and use, providing very effective metal contamination protection.  For further information or to discuss a specific application, please contact us on:


Getting Metal Out of Grain and Cereals

A Guide to the Ideal Location for Magnetic Separators and Metal Detectors in a Grain and Cereal Processing Plant

By the time grain and cereals have been collected and delivered to a Milling Plant, it is highly likely that there is metal contamination present.  Removing that metal to prevent damage to processing equipment and to produce the highest quality end-product is essential and achieved with a series of different designs of Magnetic Separators and Metal Detectors.

Grain Processing Plant Bunting Magnetics Europe Ltd
A plant flow sheet illustrating the ideal location for Magnetic Separators and Metal Detectors to remove metal contamination from Grain and Cereals

Metal can be removed at various locations within a plant, as this guide illustrates.

Step 1 – Whole Wheat Receipt

Material being discharged from the back of the transportation can be fed through a heavy duty Grate Magnet, to catch larger tramp ferrous metal.  The grain is then conveyed and fed into an elevator, where a Plate Magnet can be positioned on the side of the receiving hopper to capture smaller ferrous metals.  Another option is to install a Magnetic Separation Pulley on the end of the conveyor.

Step 2 – After Wheat Blending Silos

A second Plate Magnet can be positioned on the side of the receiving hopper of the second elevator after the wheat has been discharged from the blending silos.  This removes any ferrous metal contamination that has been liberated during the blending process.

Another option is to install a Hump Magnet, which comprises of two Plate Magnets offset inside a doglegged housing, as the elevated wheat is discharged from the elevator into the Mill Mix Silos.

Step 3 – After Mill Mix Silos

Before the wheat mix is fed into a series of screens, aspirators and the de-stoner, a Plate Housing Magnet is ideal to remove any potentially damaging ferrous metal.  Often a Plate Magnet is also installed after passing through this stage of processing and separation, on the side of the hopper feeding the next elevator.

Step 4 – After the Tempering Silos

After the tempering silos there is a stage of more delicate processing with expensive and delicate processing equipment such as roller mills, sifters and purifiers followed by reducing rollers.  It is critical that metal does not enter this stage and due to the importance a series of high strength, deep field, Plate Housing Magnets are commonly installed above the start of the process (ie the Roller Mills).

Step 5 – Fine Material After the Reducing Rollers

At this stage, the material has been significantly reduced in size and different designs of Magnetic Separator are required to remove smaller and weakly magnetic particles.  After the reducing rollers, a Drawer Magnet is commonly installed, with banks of high strength Rare Earth Tube Magnets.  After the material is bleached and whilst being pneumatically conveyed, In-line Magnets, either of a Center Flow or Pneumatic design, are connected into the pipeline.

Bunting Magnetics In Line Magnet-25

Step 6 – Coarser Bran after the Purifier

The purifier will separate the bran fraction which will be fed over a Plate Magnet prior to storage and then despatch.

Step 7 – Prior to Despatch and Packing

After enrichment, the various products are ready for despatch.  If the flour is being fed under gravity into a transport vessel, then a Drawer Magnet is commonly used as a last final stage of protection against metal contamination.  This removes any metal introduced during the process.  If the flour is being pneumatically transported into a transport vessel, then the Center Flow In-Line Magnet is commonly used.

Bunting Grate Magnet
Grate Magnets or Magnetic Separators to capture ferrous metal contamination from free flowing materials

Where flour is being packed on site, a Quicktron Metal Detector is used to detect and remove both ferrous and non-ferrous metal particles, with a final check of the packed material being undertaken using a Metron Metal Detector.

The sequence of different designs and types of Metal Separator ensures that metal being introduced as any stage of the process (ie with the original feed material and during the process) is identified and removed.  Removing metal at various stages reduces the damage to processing equipment and ensures productivity targets are met.

For further information on removing metal from a Grain Process or any food production plant, please contact the Bunting Technical Sales team on:

Phone: +44 (0) 1442 875081

Fax: +44 (0) 1442 875009