From plantation to sterilizer, every drop, jolt, and hour shapes crude palm oil quality. Data shows bruised fruits can spike free fatty acids within minutes, putting design of ramps and conveyors under the spotlight.
The palm oil mill cannot upgrade bad fruit. As the FAO puts it, the mill “cannot improve crop quality, only prevent or minimise further deterioration” (FAO). That makes the short window between cutting fresh fruit bunches (FFB, whole clusters of palm fruit) and sterilization decisive.
What happens in that window is measurable. Bruised palm flesh converts oil to free fatty acids (FFA, a quality-limiting breakdown product) fast. One study tracked ~0.11% FFA per minute in the first 15 minutes on an exposed conveyor, with a plateau only after ~6–8 hours (Tan et al., 2023; MDPI).
The upshot: mills aim to sterilize within ~24 hours of harvest (“duration from harvest to sterilization of fruits is not more than a day,” Nizam et al., 2020). In practice, that means same-day processing whenever possible. Time is fruit.
Harvest selection and gentle handling
Quality starts in the field. Harvesters cut only optimally ripened palms—typically defined as ≥5 loose fruitlets per bunch—and avoid under-ripe fruit (FAO). Once cut, bunches are handled gently: no dropping, throwing, or dragging. Heavy bunches bruise easily; studies show throwing into trucks significantly increases bruising, which then accumulates during unloading (ResearchGate; ResearchGate).
Recommended practice includes carrying or placing FFB in crates or on trolley decks, cutting stalks short (≤2 cm), and keeping vibration low. Loose palm fruit (individual fruitlets) are collected separately because they contain high oil content but form FFA very quickly; they are sent immediately to the mill and not mixed with main FFB (MDPI; MDPI).
During transit, bins are covered—tarpaulin or enclosed—to block rain, mud, or bird droppings from contacting fruit (Sharif et al., 2017).
Harvest-to-sterilization time targets
Delays are costly because FFA rises rapidly once fruit is bruised. Intact, undamaged fruit typically sits around ~0.2–0.7% FFA; crushing or fast deterioration can push FFA to several percent within an hour. One test saw a bruised fruit jump from ≈1% to 6% in just 20 minutes (Krisdiarto & Sutiarso, 2016).
Mills therefore strive to sterilize all fruit within ~24 hours, with studies noting “duration from harvest to sterilization of fruits is not more than a day” (ResearchGate). Aging fruit for 16–24 hours before processing caused a “significant increase” in FFA (ResearchGate). Edible-grade crude palm oil (CPO) is ≤5% FFA; mills aim to keep incoming FFB near ~3% or lower (ResearchGate; MDPI).
Comparative truck data underline the point: bottom-layer fruit in a full load—typically the longest-waiting and most compressed—reached ~2.79% FFA versus ~0.64% at the top (ResearchGate). Many estates adopt 6–12 hour harvest cycles, use night transport, or deploy mobile sterilizers to deactivate lipases quickly. Every additional hour typically cuts effective oil yield and raises refinery costs to neutralize FFA.
Field transport and weighbridge flow
In-transit handling stays gentle. Trucks are kept mechanically sound (shock absorbers, controlled braking), routes avoid rough roads, and loading avoids crushing; wooden stakes or slatted boards can separate layers. Covered bins prevent contamination (Sharif et al., 2017).
At the mill, weighbridge delays are kept brief. Scheduling and communication spread arrivals through the shift to avoid truck queues and rushed dumping; if queues build, some mills shade waiting vehicles. Once positioned on the ramp, trucks are secured and unloaded promptly.
Loading ramp platform and gate design
The loading ramp is a quality gate. Modern setups use a hydraulic platform or “catwalk” with multiple discharge gates—often 10–14—above belt conveyors. One lane opens at a time so bunches flow slowly onto the belt, creating a controlled, distributed discharge rather than a single dump. Hydraulic actuation and sturdy railing prevent abrupt falls.
Underneath, wide rubber belts—often >3 ft wide—with textured surfaces grip bunches. Belt speeds sit around ~1–1.5 m/s to prevent skidding and piling. Ramp floors are slightly sloped toward the gates but not steep, and short aprons or feed hoppers guide fruit onto the belt. Impact-absorbing features—chains or netting—can break the fall, and capstans or wheel blocks hold the truck steady.
Empirical guidance is clear. Tan et al. identify “the conveyor system in the mill” as “the prime area to focus on in terms of FFA reduction,” since significant bruising occurs here (MDPI). Krisdiarto et al. stress cumulative damage: bruising at unloading cascades through the system and recommend designs and practices that “avoid high impact when dropping and throwing the fruit” (ResearchGate). Lane‑by‑lane, hydraulically braked discharges and belt‑loaders or elevator conveyors that remove fruit quickly help prevent piling.
Conveyors and transfer point parameters
After the ramp, incline conveyors are kept to moderate angles (≤30°) and fitted with cleated belts or flights to prevent sliding. Transfer points minimize vertical drops with chute linings or suspended curtains to slow descent, and angled or spider‑vaned belt ends reduce shearing bruises.
The payoff is quantifiable. Fruit stuck at the bottom of a piling conveyor shows higher bruise indices, driving FFA increases; smooth, continuous flow reduces damage (ResearchGate; MDPI). Mills upgrading ramps and conveyors—smoother transitions, sensors to prevent overfilling—frequently see a few percent improvement in oil extraction rate and lower FFA in crude oil. Well‑engineered intake protects safe incoming FFB (~3–4% FFA, and ≤5% for CPO) and helps protect up to 23–24% theoretical oil yield from being lost in refining.
Summary of operational priorities
Strict harvest protocols, covered and gentle transport, and controlled, low‑impact ramp and conveyor design preserve oil quality. Studies repeatedly show each hour of delay and each free‑fall drop raises FFA—e.g., ~0.11% FFA per minute in the first 15 minutes for bruised fruit (MDPI)—while same‑day processing, covered vehicles, multiple hydraulic ramp gates, wide slow belts, and avoidance of crushing keep fruit within spec. Implemented well, these measures lift CPO output and reduce refining losses, aligning with FAO guidance and mill studies (FAO; ResearchGate; ResearchGate; MDPI).
Source references
Core sources include peer‑reviewed studies and industry reports: Indonesian research showing delayed and rough handling raises FFA (ResearchGate; ResearchGate), Malaysian mill research linking conveyor bruising to FFA spikes (MDPI), and guidance on covering fruit in transit (ResearchGate). Additional citations: Nizam et al. (2020) (ResearchGate); Krisdiarto & Sutiarso (2016) (ResearchGate; ResearchGate); Sharif et al. (2017) (ResearchGate; ResearchGate); Tan et al. (2023) (MDPI). For overall context: FAO.
