Colour Sorters
Colour sorters are used to remove defects and foreign material (FM) from many foodstuffs worldwide. Colour sorting is particularly suitable to automate manual inspection of fresh fruit and vegetables such as carrots, potatoes, peas and beans coming direct from the field to remove extraneous vegetable matter (EVM) and gross defects, stones, sticks and so on that are picked up with the harvest. Other harvested products such as nuts, seeds and grains are also colour sorted as part of the post-harvest removal of husk, dust, stones etc. Colour sorters give the packer or processor labour saving and efficiency of operation for added value and cost savings over traditional methods of inspection.
Sorters inspect a huge range of processed and baked products on an industrial scale in widely diverse food sectors including rice, coffee beans, nuts, tea leaves, lettuce and salads, shredded cheese, baked beans, crisps and snacks after cooking and removing broken and wrongly filled or coated biscuits, and all of these prior to packing. French fries are sorted to remove colour defects from the potato strips and check their length profiles and many frozen and cut vegetables including mixes of diced carrot, potato, peas etc are inspected immediately prior to packing.
Colour sorters use high speed digital signal processing to scan the product stream on a wide flat belt or chute using black and white, colour cameras or infrared and ultraviolet lighting systems, or lasers, and other optical sensors. The product images are compared to stored profiles of the acceptable product limits and reject defects not recognised as good product. Very often the defect is removed from the line by one of an array of high speed air ejectors positioned just downstream of the cameras and many thousands of or a flap or other bulk defect gate. Good product continues out of the sorter to packing. Some sorters incorporate recovery systems for re-inspecting the defects.
Colour sorting techniques are also widely used in other industries, in recycling for example to remove green glass from white glass and in the tobacco industry to remove foreign matter from the shredded leaves.