Design and Testing of a Low-Cost Groundnut Oil Expeller for Rural Processors in Gombe State

Groundnut oil extraction in Gombe State, North East Nigeria, is predominantly conducted by small-scale processors using manual pressing methods that yield low extraction efficiency and poor product quality. This study designs, constructs, and tests a low-cost motorised screw-press expeller using locally sourced materials including mild steel and fabricated parts from Gombe market workshops. The expeller was evaluated using groundnut kernels of known moisture content, testing extraction efficiency, oil yield (percent), free fatty acid content, peroxide value, and throughput capacity. Optimisation experiments varied feed moisture content (4 to 10 percent wet basis), screw speed (40 to 80 rpm), and barrel temperature (60 to 120 degrees Celsius) using a Box-Behnken experimental design. The optimal conditions identified were 8 percent moisture, 60 rpm, and 100 degrees Celsius, yielding an oil extraction efficiency of 88 percent with a free fatty acid content of 1.2 percent and a peroxide value of 6.4 meq/kg, both within acceptable limits. Throughput was 25 kg of kernels per hour. The expeller fabrication cost was estimated at 180,000 Nigerian naira, with a payback period of 11 months for processors handling 50 kg of kernels per day. The study draws on recent literature on small-scale oilseed processing technology. Findings are intended for the Gombe State Agricultural Development Programme and rural technology dissemination initiatives. Keywords: groundnut oil, expeller, extraction efficiency, fabrication, Gombe State