This palm fruit sterilization step in the palm oil extraction process is crucial to the final oil quality as well as the strippability of fruits. Sterilization inactivates the lipases in the fruits and prevents buildup of free fatty acids (FFA). In addition, steam sterilization of the FFBs facilitates fruits being stripped from the bunches. It also softens the fruit mesocarp for digestion and release of oil, and conditions nuts to minimize kernel breakage.
In recent years, new technology on sterilization saw the introduction of continuous sterilizers. Continuous sterilizer showed improved fruit strippability, even with usage of low-pressure steam or atmospheric steam. The new system consists of conveyor belts taking crushed FFBs into the continuous sterilizer, where the fruits are sterilized and subsequently discharged. This reduces much of the machinery associated with conventional sterilizers. In addition, there are cost savings in terms of manpower requirements, and maintenance.
The following discussion on the different types of sterilizer:
The horizontal sterilizer is the most commonly used sterilizer in palm oil mills. When disposed in a horizontal position, the cylindrical vessel sterilizer has fairly good disposition because the oil palm fresh fruit bunches placed in cages with a low stacking height are more uniformly spread out in this position across the length of the elongated vessel, as opposed to a vertical sterilizer. Thus, when pressurized steam is injected into the interior of the horizontally positioned cylindrical vessel, the steam can reach out to different directions and corners of the contents within the cages thereby helping treatment of the fruit bunches. Due to the low stacking height of the fruit bunches in the cages, condensate drains out freely from the fruit bunch stack facilitating heat penetration. The low stacking height also limits fruit bunch compression that facilitates low oil loss from the fruits during sterilisation.
Vertical sterilizers are available in several variations where fresh fruit bunches are placed directly into a tall vertical vessel without steel cages. The vertical sterilizer is considered for use in palm oil mills where space saving is important. Vertical sterilizers are much cleaner and easier to operate than conventional sterilizers.
Another type of sterilizer technology, the Tilting sterilizer eliminates much of the machinery associated with conventional sterilizers. The technology is the latest design that offers improved milling efficiency, and reduced labour and maintenance cost.