Keyword: processing, fresh fruit bunch (FFB), milling, sterilization, clarification, purification, digestion

The main stages of processing FFBs are: –

(i) Sterilization

Fruit bunches are sterilized by steam at about 140°C for a period of 75-90 minutes. The main objectives are to deactivate hydrolytic enzymes responsible for the breakdown of oil to free fatty acids; to loosen the fruits from bunches; to coagulate mucilage to facilitate breaking of oil cells and aid recovery of oil; and precondition nuts to minimize kernel breakage.

(ii) Bunch Stripping

The fruits are stripped and separated from the bunch in a rotary drum stripper. Fruits are knocked out of the bunch by the lifting and dropping of bunches as they pass through the stripper. The detached fruits fall through the spaces between the bars on the stripper and are collected in a conveyor, which then feeds them into the digester.

(iii) Digestion

Digestion involves the mashing up of the fruits under steam heated conditions. The digester is a vertical cylindrical vessel fitted with a rotating staff carrying a number of stirring arms. The action of the stirring arms breaks up the oil-bearing cells of the mesocarp to form a digested mash.

(iv) Oil Extraction

Twin screw presses are generally used to press out the oil from the digested mash. Hot water may be added to enhance the oil flow and the crude oil slurry is collected in the crude oil tank for purification. The fibre and nut (press cake) are conveyed to depericarper for separation.

(v) Clarification and Purification

The crude palm oil (CPO) mixture from the screw press consists of a mixture of crude oil (35-45%), water (45-55%) and fibrous materials and other solids in varying proportions. The mixture is pumped into a continuous clarification tank. The oil is maintained at about 90°C to enhance oil separation. The oil is continuously skimmed off the top of the tank while the denser impurities settle at the tank bottom. The oil is passed through a high-speed centrifuge and a vacuum dryer to a moisture content of below 0.1% before being sent to the storage tank.