Stones are a frequent foreign matter in coffee. They can be more easily removed from roasted coffee than from green coffee, since the roasting process reduces the specific weight of the coffee. The stone separator therefore functions on the principle of gravity: the coffee is placed on a sieve, which is set in vibration via a crankshaft drive. Airflow passing upwards produces a fluidised bed on which the coffee beans “float,” while stones and other heavy foreign bodies remain on the sieve and are conveyed by vibrations to an outlet. Lighter-weight particles (chaff, scraps of paper or similar) are suctioned off.

The high-suction destoners are employed in particular to clean roasted coffee. While the beans, which have been made lighter and larger by roasting, are conveyed upwards pneumatically, gravity forces foreign bodies of higher density – stones, in particular – to remain on the floor and then be disposed of.

• Stone separator  
• Metal eliminator  
• Dust extraction unit
• Colour sorter