Before passing the seeds to decortications machines, it should pass through the de-stoner machines, which will remove the stones of the seed size, which have passed through pre-clean- ing machines.

Certain Seeds like Ground-nuts, Castor and Cotton Seeds have outer covering known as shell or husk. This husk contains practically no oil and represents approximately 30% of the wei-ght of the seed. Its removal before crushing is important due to the following reasons :

It increases the pressing capacity of the mill. If husk is allowed to be pressed, it forms the part of the cake and absorbs oil to an extent as would be lost in the cake. This, therefore  results in the low yield of the oil. The presence of husk in the seeds also impart color of the oil. The husk being of siliceous nature, have a detrimental effect on the expellers. The decorticator machines setting needs checking very often to ensure that husk do not carry small kernel particles, which otherwise is a direct loss.

In these machines the seeds are passed through special rollers set-up with cutting edges and ridges which causes break in their shells, while the seed remains un-touched. Various types of machines are used to decorticate depending on the size and nature of the seed. Various makes of groundnuts decorticators, castor seed sellers & cotton seed hullers are available in the market. After breaking the husk, the seeds are cleaned by blowing the husk carefully.