Processing of Oil Palm
The sequence of processes involve in the industrial/large scale extraction of oil palm to produce a high yield of internationally acceptable quality. These are:
1. The reception of fresh fruit bunches from the plantations
The quality standard achieved is initially dependent on the quality of bunches arriving at the mill. The mill cannot improve upon this quality but can prevent or minimize further deterioration. Adequate care should be taken during harvesting and transportation of the fruit to avoid excessive bruising; resulting in oil of reduced quality.
2. Threshing of bunches to free the palm fruit
This involved the removal of the fruits from the spikelets growing on a main stem. It can be achieved manually using cutlass or axe, the fruits are then handpicked. In a mechanized system a rotating drum or fixed drum equipped with rotary beater bars detach the fruit from the bunch, leaving the spikelets on the stem.
Sterilization or cooking means the use of hightemperature wetheat treatment of loose fruit. The cooking serves the following purposes:
♦ Heat treatment destroys oilsplitting enzymes and arrests hydrolysis and autoxidation.
♦ Heat allows the oilbearing cells to come together and flow more easily on application of pressure. ♦ Fruit cooking weakens the pulp structure, softening it and making it easier to detach the fibrous material and its contents during the digestion process. Making the oil to be released more readily.
♦ The moisture introduced by the steam acts chemically to break down gums and resins which cause the oil to foam during frying.
4. Digestion of the fruit
Digestion is the process of releasing the palm oil in the fruit through breaking down of the oilbearing cells. The digester is usually made up of cylindrical vessel fitted rotating shaft carrying a number of beaters. Through the action of the rotating beater arms the fruit is pounded.
5. Pressing (Extracting the palm oil)
There are two methods which can be employed in extracting oil from digested material. One system uses mechanical presses and is called the ‘dry’ method. The other called the ‘wet’ method uses hot water to leach out the oil.
In the ‘dry’ method, the oil is squeezed out of a mixture of oil, moisture, fibre and nuts by applying mechanical pressure on the digested mash.
6. Clarification and drying of oil
This process ensures the oil is separated from its impurities. The fluid coming out of the press is a mixture of palm oil, water, cell debris, fibrous material and ‘nonoily solids’. Hot water is added to the thick mixture in the ratio 3:1. The diluted mixture is passed through a screen to remove coarse fibre.
The screened mixture is boiled from one or two hours and then allowed to settle by gravity in the large tank so that the palm oil, being lighter than water, will separate and rise to the top. The clear oil is decanted into a reception tank. The decanted oil is reheated in a cooking pot and the dried oil is carefully skimmed off from any residual moisture.
7. Oil storage
The purified oil is transferred to a tank for storage prior to dispatch from the mill. The stored temperature are maintained around 50°C using hot water or low pressure steamheating coils, to prevent solidification and fractionation. Iron contamination from the storage tank may occur if the tank is not lined with a suitable protective coating.
Processing of Oil Palm