Pressing sits at the heart of every palm oil mill. After sterilization and threshing, the digested fruit mash must be pressed to separate crude palm oil (CPO) from fiber and nuts. The choice of press machine—most commonly hydraulic or screw—shapes extraction efficiency, operating cost, product quality, and how easily your mill scales or automates. This guide explains how each press works, where it fits best, and how to choose confidently for new builds or upgrades. Where the Press Fits in the Line A typical flow is: FFB reception → Sterilization (steam) → Threshing → Digestion (heating + mechanical mashing) → Pressing → Clarification & Purification → Storage. The press must accept hot, well-digested mash (usually ~90–100 °C), create adequate compression to express oil, and discharge a press cake that is dry enough to minimize oil losses but still suitable for downstream kernel recovery. Hydraulic Presses How they work Hydraulic presses apply force intermittently using a hydraulic cylinder acting on a ram. Mash is loaded into a cage or basket (often lined with perforated plates). The ram compresses the mash, oil drains through perforations to a collection channel, and the ram retracts so operators can open the cage and reload for the next cycle. Some mills use multi-ram or carousel arrangements to raise throughput. Typical configuration Batch operation (manual or semi-automatic). Simple hydraulics (pump, reservoir, control valves), welded frame, perforated cage, and drain channels. Small installed motor power, but cycle-time dependent throughput. Best suited to village-scale or artisanal production, pilot plants, or specialty lines. Strengths High unit pressure is possible on a compact footprint. Simple mechanics; straightforward to understand and maintain. Low acquisition cost for small capacities. Flexible—can handle variable feed characteristics without complex controls. Limitations Batch, stop-start workflow limits capacity and raises labor per ton. Inconsistent cake dryness and higher residual oil than continuous screw presses in most cases. Harder to integrate into fully automated lines; operators handle loading/unloading. If cycle times are long, FFA may rise due to warm holding of mash before pressing and more exposure to air. Wear and cleaning of perforated baskets can be labor-intensive. Best fit: micro or cottage mills; R&D; locations with intermittent power; mills valuing low capex more than maximal recovery. Screw Presses Screw presses are continuous machines that dominate modern industrial palm oil mills. Two main styles are used: Single-Screw Press (worm press) Double-Screw (Twin-Screw) Press with intermeshing counter-rotating screws Core principle A rotating screw (or screws) conveys hot mash through a cylindrical cage with drainage slots or bars. The flight geometry, pitch reduction, and barrel clearance progressively compress the mash. Oil drains through the cage; solids exit as a compact press cake. Proper digestion and feed temperature are critical to reduce torque spikes and improve oil release. Single-Screw Press One rotating worm shaft inside a slotted cage. Throughput commonly 5–10 t FFB/h per unit (smaller/larger variants exist). Mechanical simplicity, wide parts availability, proven in thousands of mills. Pros: economical, simpler maintenance, modular capacity (add more units), good integration with conveyors/PLCs. Trade-offs: slightly higher residual oil vs. a well-tuned twin-screw; more torque concentration along one shaft demands a robust gearbox and periodic hardfacing of flights and cage bars. Double-Screw (Twin-Screw) Press Two intermeshing, counter-rotating screws; mash is compressed between the screws and against the cage. Per-unit capacity often 10–25+ t FFB/h. More uniform shear/compression, typically drier press cake (lower residual oil). Pros: high throughput, higher oil recovery (lower residuals), stable operation at large scales, favorable cake dryness for kernel recovery. Trade-offs: higher capex, more complex mechanics (two shafts, gear train), higher installed power, skilled maintenance required. Side-by-Side Comparison Operating mode, yield, energy, and maintenance Factor Hydraulic Press Single-Screw Press Double-Screw Press Operation Batch (intermittent) Continuous Continuous Typical Unit Capacity 0.3–3 t/h (batch-dependent) 5–10 t/h 10–25+ t/h Extraction / Residual Oil Variable; generally higher residuals Good-tuned units perform well Best, typically lowest residual Cake Dryness Variable; depends on cycle control Good Very good Energy (Installed Power) Low per unit energy/ton varies with cycle ~20–50 kW per unit ~60–100+ kW per unit Labor Requirement Higher (loading/unloading) Moderate Moderate Maintenance Hydraulics + cage cleaning Wear on worm flights, cage bars, and bearings More parts: two screws, gears, bearings Automation Limited; semi-auto possible Easy to integrate with PLC/SCADA Easy to integrate; complex interlocks Capex Low (small scale) Moderate Highest Best Use Case Village/pilot Small–medium mills Medium–large mills Note: Actual capacities and kW ratings depend on fruit quality, digestion, screw geometry, cage gap, and line design. Quality Impacts: Oil, Nuts, and Clarification Oil Quality (FFA, impurities): Continuous presses shorten exposure of hot mash to air vs. batch queues, helping limit FFA rise. Proper screening and dilution after pressing still determine the clarification load. In general, screw presses (especially twin-screw) deliver more consistent oil flow with fewer big slugs of fines than manual hydraulic cycles. Press Cake & Kernel Recovery: Drier cake improves nut–fiber separation and kernel recovery efficiency. Twin-screw presses usually give the driest cake, aiding downstream depericarper and nut crackers. Wear Metals & Contamination: Flight/cage wear can shed particles. Specify hardfaced, food-contact-appropriate materials, maintain bar gaps, and implement magnetic traps or strainers before clarification. Energy & Throughput Hydraulic presses often show low installed motor power, but the intermittent duty and longer warm dwell times can increase energy per ton (stop-start losses, longer heating). Single-screw units (approx. 20–50 kW each) suit modular lines; you can parallelize presses to match sterilizer capacity. Twin-screw units (approx. 60–100+ kW) deliver more tons per unit, frequently lowering energy per ton at high throughput despite higher nameplate kW. Spares and Reliability Hydraulic Press Critical spares: cylinder seals, pumps, valves, pressure gauges, cage liners. Failure modes: seal leakage, pressure loss, frame alignment drift. PM tasks: oil cleanliness checks, seal inspection, bolt torque verification, safety relief tests. Screw Press Critical spares: worms (several stages), cage bars, press cone, bearings, shaft sleeves, gearbox internals, V-belts/couplings. Failure modes: excessive wear → rising power draw and oil loss; cracked bars; cone seizure. PM tasks: daily cleaning of slots, weekly cone checks, scheduled worm/bar replacement, gearbox oil