Colour sorting for the bulk food industry

Good food can usually be distinguished from bad food by colour. This may appear to be an obvious statement, but the implications for the food industry are significant. Human perception of colour has proved very effective in determining food quality. Sorting of food products using the human eye and hand is still widely practised in regions where labour rates remain low. However, where the cost of labour has increased, so automated teehniques have been introduced. 

Colour sorters generally consist of four principal systems  

Figme 6.1 shows a typical layout for an optical sorting machine. 

In a bulk sorting system, dry products (rice, coffee, nuts) are fed from a vibrating hopper onto a flat, or charmelled, gravity chute. To prevent excessive clumping. 

The ejection system must be capable of physically removing unwanted product items from the main accept stream. The ejection process typically takes place while the product is in free fall accept particles are allowed to continue along their normal trajectory, and rejects are deflected into a receptacle. Deflection is usually achieved by emitting short bnrsts of compressed air through nozzles aimed directly at the rejects, althongh large or heavy objects (e.g., whole potatoes) may reqnire some sort of piston-operated device to mechanically deflect the rejects. 

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