Introduction
Palm oil is extracted from fresh fruit bunches (FFB) by mechanical process, where a mill commonly handles 60 to 100mt per hour of FFB. The modern palm oil mill of today is based predominantly on concepts developed in the early 50s (Mongana Report). An average size FFB weighs about 20-30kg and contains 1500-2000 fruits (Figure1). The FFBs are harvested according to harvesting cycles, and delivered to the mills on the same day. The quality of crude palm oil is dependent on the care taken after harvesting, particularly on the handling of the FFBs.
Figure 1. Fresh fruit bunches waiting for processing at palm oil mill
A palm oil mill produces crude palm oil and kernels, as primary products and biomass as secondary product. The capacity of mills varies between 60- 100 tons FFB/h. A typical mill has many operation units as shown in Figure 2. This comprises of sterilization, stripping, digestion and pressing, clarification, purification, drying and storage. For the kernel line, there are steps such as nut/fibre separation, nut conditioning and cracking, cracked mixture separation, and kernel drying, storage. The dried kernels are often sold to palm kernel crushers for extraction of crude palm kernel oil. In some integrated plants, kernel crushing facilities exist side by side at the same complex.
Figure 2. Flow chart for the palm oil process (from Sivasothy, 2000).
Sterilisation
This first step in the process is crucial to the final oil quality as well as the strippability of fruits. Sterilization inactivates the lipases in the fruits, and prevents build-up 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 conditioning of nuts to minimize kernel breakage. Air is removed from the sterilizer by sweeping in steam in single-peak, double-peak or triple-peak cycles. In general,