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INTERDISCIPLINARY JOURNAL OF CONTEMPORARY RESEARCH IN BUSINESS
8.1 KERNEL PRE-TREATMENT
Proper kernel pre-treatment is necessary to efficiently extract oil from the kernels. the
feed kernels must undergo such pre-treatment as dehaulling, cleaning, destining, cooking
/ heating , drying to optimum moisture/temperature levels and flaking. foreign materials
are removed during the process of cleaning to avoid damaging of the screw presses,
increasing cost and downtime and contamination of the products.
A swinging hammer grinder, breaker rolls or the combination of both breaks the kernels
into small fragments. This process increase the surface area of the kernels, thus
facilitating flaking. The kernel fragments subsequently are subjected to flaking in the
roller mill. The thickness of the kernel cake is progressively reduced as it travels from top
roller to the bottom roller. This progressive rolling initiates rupturing of the cell walls.
The flakes at the bottom nip are from 0.25mm to 0.4mm thick(Golden oil,2002). The
kernel flakes are then conveyed to a stack cooker for steam conditioning; the purpose of
which is to:
� Adjust the moisture content of the meal to an optimum level
� Rupture the cell wall of the palm kernel, initiated by rolling.
� Reduce viscosity of the oil.
� Coagulate the protein in the meal to facilitate oil separation from protein material.
The meals are normally cooked to a moisture content of 3 % at 104-1100C.
8.3 SREW-PRESSING
The properly cooked meal is fed to the screw press, which consist of an interrupted
helical thread (worm); which revolves within a stationary perforated cylinder called the
cage or barrel. The meal is forced through the barrel by the action of the revolving
worms. The volume axially displaced by the worms diminishes from the feeding end to
the discharge end, thus compressing the meal as it passes through the barrel.
The expelled oil drains through the perforation of the lining bars of the barrel while the
de-oiled cake is discharged through annular orifice. In order to prevent extreme
temperatures that could damage the oil and cake quality, the worm- shaft is always
cooled with circulating water while the barrel is cooled by recycling some cooled oil. The
following facts can be drawn from the concept of screw pressing:
� With increasing pressure the yield increases reaching a limit at higher pressures. This
limit is dependent on the type of seed, seasonal variations, pre-treatment of the seed
and the equipment used. Most data available in literature are limited to pressures
below 35 MPa, with a few exceptions(.; Ford, R. J.; Wulfsohn, D.; Bargale, P. C
Irudayaraj, J.; Sosulski, F. W.Journal of Agricultural Engineering Research 2000.)
� Quality requirements for the oil or the meal may restrict the maximum allowable
temperature to prevent undesired cell wall components polluting the oil. It is therefore
desirable to reach high yields at lower temperatures.
� Starting from dry seeds, increasing the moisture content (MC) of the seeds increases
the yield until a seed-specific maximum. Increasing the moisture content beyond this
optimum decreases the yield again. This is due to two counteracting phenomena.
Increasing the moisture content of the seeds is reported to make the cell walls more
permeable (Bargale, P. C.; Singh, J. Journal of food science and technology 2000),(
which increases the yield), but also, to cause a plasticization of the seed material
COPY RIGHT © 2011 Institute of Interdisciplinary Business Research 66
JANUARY 2011
VOL 2, NO 9