Spotlight on sorting: What nut processors can gain from the latest sorting technologies

The TOMRA 5C is one of the company’s many sorters that can detect minute imperfections in nuts

Nut processing is wrought with overwhelming health and safety challenges ranging from foreign bodies to deadly toxins that can make or break food producers. TOMRA Food sorting technologies offer a thorough solution so manufacturers can have a greater piece of mind.

It is not easy for nut processors to ensure food safety or meet customers’ product specifications – foreign material and shell fragments can get into the processing line’s product stream, and nuts can be damaged by both by external and internal defects that are almost impossible to detect. There is also the risk posed by allergens if one type of nut should be unintentionally mixed with another. All of these threats have to be eliminated to protect processors and retailers from product recalls and reputational damage.

The removal of these threats and defects are achievable thanks to state-of-the-art optical sorting machines. Today’s sorting solutions deliver a multitude of other benefits: they grade to specification, minimise false rejects, increase removal efficiency, reduce or eliminate the need for manual intervention, help solve the problem of labuor (scarcity, cost, effectiveness), reduce downtime, and provide data about the product being sorted. Through these capabilities, sorters improve sustainability by cutting food waste while enhancing yields and profits.

This article spotlights sorters’ capabilities with four popular types of nut to see the sorting solutions offered by industry-leader TOMRA Food, looking first at almond processing to introduce and explain the technologies applicable throughout its various stages. Walnut, hazelnut and peanut processing will also be examined.

Different sorters for different tasks  

As harvested nuts are hulled, shelled then processed, different sorting solutions are needed to perform various tasks. Sorting machines initially take care of fairly basic requirements, but as nuts progress towards storage or packaging, the sorters become more sophisticated and specialised in their focus. The process for almonds is a good example.

With almonds, the removal of foreign material, hull and shell, is a challenge the huller-sheller typically deals with. A highly detailed inspection is not needed at this initial stage, but it is desirable to sort out the bigger pieces of unwanted material, and quickly. The machine best suited to this task is the TOMRA 3C, a free-fall machine capable of sorting more than 20 tons of nuts per hour. With an incredible efficiency of 99.5%+ purity, foreign materials, including hull, stone and most common defects are eliminated.

A second check for foreign materials and kernels is made when the almonds reach the processor – more sorting is done here to prevent later work. Handled by TOMRA’s Ixus Bulk sorter, a belt machine capable of unrivaled throughput, it employs the latest x-ray and imaging technology to detect and eject materials such as stones, glass and high-density plastics.

The sorter then looks for smaller and less dense foreign materials. Plastics might still be found, but most unwanted objects are now likely to be natural materials such as shell, small sticks or allergens arising from cross-contaminated products – a pistachio in an almond line, for example. The machine that performs this task is the TOMRA 5C, a premium optical sorter explicitly developed for nuts and dried fruit, recently launched as the successor to the TOMRA Nimbus. The TOMRA 5C is typically equipped at this point in almond processing with a single laser scanner plus a single BSI+ scanner uniquely capable of ‘seeing’ the biometric characteristics of materials on the line, using two different technologies to ensure removal of all types of foreign material.

For the third sorting stage at the almond processor, the TOMRA 5C is used again – equipped with two Biometric Signature Identification (BSI+) scanners, it can find hard-to-see and nearly invisible defects: insect damage, pin-hole, gummy, mold, brown spot, and shrivel. Though nuts with these defects are removed, they will be recovered for sale for other uses. Most defects at this stage are inedible and will be used in oils for cosmetics.

TOMRA’s unique BSI+ technology scans materials with both near-infrared (NIR) and visible spectrum wavelengths, making it possible to find these defects. It instantly compares the biometric characteristics of objects to features stored in a database to determine whether they should be accepted or rejected. Other critical nut defects such as rancidity, decay, mold, allergens, and water and oil content are also detected and rejected.

After the almonds have been mechanically sorted according to size, they will once again be run through a TOMRA 5C with full-option double laser scanners and double BSI+ scanners, looking for the most difficult to remove, very small defects such as pin-hole and embedded shells. Immediately before the nuts are shipped to market, they will be checked one more time for cosmetic imperfections such as chips and scratches by the TOMRA 5B, a belt machine that combines 360-degree surround-view technology with advanced shape algorithms for object processing. This sorter is ideal for the targeted identification of individual defects in high-volume production flows. The defect in this case is purely cosmetic and the rejected product will retain its delicious taste and high nutritional value in manufactured products.

Multiple checks for walnuts too

Walnuts are sold in so many different sizes, grades, and product types that they are the most complicated of all nuts to process. Booming global demand for walnuts creates a need to process them in ever-greater quantities, while consumers are simultaneously raising their expectations of product quality and food safety. This is seen in product specifications getting stricter: not long ago it was acceptable for a ton of nuts to contain up to 20 pieces of shell, but today many wholesalers insist on there being no more than five pieces per ton – or in some cases, fewer than one.

To achieve these standards, walnuts, like almonds, are typically passed through sorters six times or more. Thorough sorting also enables the recovery of nuts rejected as whole foods to be used for food ingredients, for their oils, or the cosmetics industry.

In the first stage, before cracking, the huller will put the walnuts through the Ixus Bulk x-ray sorter to remove foreign materials which could damage the shelling equipment. After sizing and shelling, the nuts are passed through a TOMRA 3C optical sorter at high capacity to remove shell fragments. Then the TOMRA 5C (or its predecessor, the Nimbus) works its magic no fewer than three times, before a final inspection is made by the TOMRA 5B. TOMRA’s ability to handle the product gently is critical in walnuts because they are quite fragile and breakage will reduce their value.

On the first run through the TOMRA 5C, when the machine is equipped with double-sided BSI+ scanners, a search is done for foreign materials, allergens, shell pieces, and shells within the walnut. On the second run, using a high-resolution double-sided laser and a single BSI+ scanner, the sorter detects and ejects hard-to-find product defects such as rancidity, mold, septa, shriveled nuts, and dark (red or black) nuts. On the third run, with the TOMRA 5C now ‘seeing’ through a double-sided laser and single BSI+ scanner, the product is graded according to colour and assessed to ensure compliance with the customer’s specification (for example, perhaps a maximum of three pieces of shell per ton is permitted). Then in the final step before distribution, the walnuts are inspected by the TOMRA 5B for grading by shape and perhaps also by colour.

Hazelnuts are not much easier

With hazelnuts, the process is equally complicated. Though usually hand-picked, processors will still need to remove many of the same defects such as stones and other foreign material. Hazelnuts will be run through a TOMRA 3C before cracking to remove unwanted items such as sticks, stones and loose kernels, then re-sorted to separate the loose kernels from the sticks and stones. Another TOMRA 3C is used after cracking, focused mainly on the shell pieces generated by the cracking process.

After this, the TOMRA 5C (or its predecessor, the Nimbus) is used at least twice, with some processors choosing to send the ejected product to another TOMRA 5C to recover what is saleable at a lower grade. Both these inspections are made with double-sided BSI+ scanners (and perhaps also a high-resolution laser), to find and remove product imperfections such as mold, shrivel, oblong, and cimiciato insect damage. Only by using TOMRA’s unique Biometric Signature Identification technology is it possible to find such damage.

Finding deadly toxin in peanuts

Of all the threats faced by nut processors, peanuts pose the most challenge as it contains aflatoxin, a naturally occurring mycotoxin which must be removed. Produced by certain Aspergillus molds (fungi) on plants such as corn and grain, or more commonly in the ground, this toxin usually develops in the field. As it tends to occur in ‘hot spots’, test samples do not always find it. But TOMRA’s Detox Machine does.

Its special design, incorporated in the TOMRA Nimbus machine, makes it possible to identify the extremely low intensity of light reflected by aflatoxin producing mold in peanuts and remove them. 

Peanut processors and retailers thus save costly product recalls and reputational damage. 

Mission accomplished with sorters

Although TOMRA’s sorting technologies are sophisticated, all are designed to be easy to use. Moreover, these machines are remotely controllable and easily networked and some even possess self-learning abilities to refine their sorting accuracy continually. Thus, false rejection rates are low, yields are high, and nut processors are empowered to conquer even the most daunting of operational challenges.

This article was first published in the December 2021/January 2022 issue of Food & Beverage Asia.