It’s not easy for nut processors to ensure food safety or meet customers’ product specifications. For instance, foreign material and shell fragments can get into the processing line’s product stream. Nuts can also be damaged by both external and internal defects which can be almost impossible to detect.

There’s also the risk posed by allergens if one type of nut should unintentionally get mixed with another. Yet all these threats must be eliminated to protect processors and retailers from product recalls and reputational damage.

If this makes nut processing sound like ‘Russian Roulette’, the good news is that it’s possible to remove all the bullets! This is achievable thanks to the extraordinary effectiveness of state-of-the-art optical sorting machines.

What’s more, 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 labour (scarcity, cost, effectiveness), reduce downtime, and provide data about the product being sorted. Through all these capabilities, sorters improve sustainability by cutting food waste while enhancing yields and profits.

This article looks at how sorters achieve all this. We highlight their capabilities with one of the most challenging nuts, walnuts, to see the sorting solutions offered by industry leader Tomra Food. The same technology can be used with almonds, hazelnuts and other nut types.

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 handle basic sorting, but as the nuts progress along the line towards storage or packaging, the sorters become more sophisticated and specialised in their focus. The process for walnuts is a good example of this.

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.

Consumers demanding tighter specifications

This is seen in product specifications getting stricter: not so 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, mould, septa, shrivelled 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.

Although Tomra’s sorting technologies are sophisticated, all are designed to be easy to use. What’s more, these machines are remotely controllable and easily networked, and some even possess self-learning abilities to refine their sorting accuracy continually.

As a result, false rejection rates are low, yields are high, and nut processors are empowered to conquer even the most daunting of operational challenges.

*Written by Brendan O’Donnell - global category director for nuts and dried fruits at Tomra Food.