Critical Extraction Parameters for Maximizing Oil Yield from Spent Coffee Grounds

Abstract

Coffee is one of the most consumed beverages worldwide, producing approximately 6 million tons of spent coffee grounds (SCG) annually, which are often discarded in landfills. SCG contains 12–16% dry basis oil, which can be recovered in various industrial processes, promoting a more circular and sustainable economy. The efficient reuse of SCG depends on the extraction methods employed. This study investigates the influence of key parameters—solvent type, extraction time, temperature, and particle size—on oil extraction, and evaluates the oil quality using FTIR. Scanning electron microscopy (SEM) was also employed to observe microstructural changes in SCG before and after extraction with both polar and non-polar solvents. Four solvents were tested across different particle sizes. The highest oil yield, 14.57 ± 0.42%, was obtained using ethanol with SCG particle sizes between 250–425 µm, 8 h extraction time, and 60 °C. However, an extraction time of 240 min was found to be optimal, yielding 94% of the oil, making it more suitable for industrial applications. For methanol, diethyl ether, and hexane, the maximum oil yields were 8.46 ± 0.49%, 13.51 ± 0.49%, and 13.51 ± 0.15%, respectively. SEM results indicated that polar solvents were more effective at breaking down SCG and extracting oil. FTIR analysis identified characteristic bands typical of vegetable oils, with no indication of phospholipid contamination.