Nutcracker
The separated nuts are passed to a polishing drum at the bottom of the depericarper,
where pieces of stalks are removed. Fresh kernels have a moisture content of about
20% and cannot be stored without deterioration (moisture content of above 7% can
encourage hydrolysis of the oil through autocatalytic and by lipolytic microorganism)
(Coley & Tinker, 2003). A nutcracker cracks the nuts after the conditioning and
drying process. A ripple mill is also used instead of nut cracker. Then the mixture of
cracked nuts and shells are separated via a winnowing system, followed by a hydrocyclone
or a clay bath. The clay bath separation technique is in the realm of traditional
method while modern mills almost exclusively use a hydrocyclones for separation
even though the clay bath system is cheaper (Corley & Tinker, 2003). A hydrocyclone
uses centrifugal force to separate the kernel from the shell using water. The clay bath
principle works on the specific gravity of kernel of 1.07 g per milliliter and the shell
of 1.17. The kernels will float while the shells sink in a clay bath mixture of specific
gravity 1.12. The kernels are then dried in hot air silos to moisture content of less than
7%. About 0.4 mt of kernels are produced with every metric tonne of crude palm oil
(CPO) (Wai-Lin, 2011). The sources of oil loss in this process are due to incomplete
cracked, un-cracked, and non-recovery of cracked nut.