Another method of extracting PKO from the cracked and separated nuts involves the
use of oil presses. There are many types of oil presses in the engineering market today,
but all work on a similar principle. The oil press consists of a heavy perforated or slotted
metal cage and a plunger while a screw press/oil expeller consist of a horizontallyrotating
screw contained in a barrel-shaped outer casing with perforated walls. A screw
press is a continuous screw auger designed to subject the oil-rich material to increasing
pressure as it is conveyed through the barrel. The barrel forms a cage of bars surrounding
the screw in a parallel fashion. The bars of the cage are separated by spacers, which
allow the oil to drain from the cage while the solids are conveyed down the barrel toward
higher pressure. The discharge opening for the reduced-oil solids and, thus, the back
pressure are controlled by a choking device. A plug of compressed oil-lean solids, termed
cake, forms at the discharge. The pressure increases down the length of the barrel by
increasing the root diameter of the screw, decreasing the pitch of the screw flights and
controlling the cake discharge opening by means of a choking device (Johnson, 2008).