Valorization of Coffee By-Products: Cascade Pathways for Food, Materials, Energy, and Environmental Applications

Coffee production and consumption generate heterogeneous biomass and effluent streams, including pulp, husk, mucilage, parchment, silverskin, spent coffee grounds (SCGs), and processing wastewater. However, the literature on their valorization remains fragmented by feedstock and application, with limited integration of safety, regulatory, and scalability considerations. This structured narrative review synthesizes recent evidence on the composition, stabilization, fractionation, and cascade biorefinery valorization of the principal coffee by-products. Current evidence most strongly supports cascade schemes in which lipids and bioactive compounds are recovered before carbohydrate- and lignin-rich fractions are directed to material, biochemical, anaerobic, or thermochemical conversion. However, while this sequence is technically feasible for SCGs, its applicability to other by-products requires further validation. Composition, moisture, stability, and contamination risks vary substantially among coffee by-products, and many reported applications remain at laboratory scale. Food uses additionally require control of caffeine, mycotoxins, process contaminants, and sensory acceptability. Cross-study comparisons are constrained by inconsistent feedstock descriptions and operating conditions, and three main limitations constrain industrial implementation: inconsistent feedstock characterization, safety concerns for food applications that remain insufficiently addressed, and scarce pilot-scale demonstrations and techno-economic assessments. Future research should prioritize by-product-specific cascade designs, standardized mass and energy balances, and safety validation. Overall, coffee by-products can function as valuable secondary resources, but their sustainable utilization requires feedstock-specific strategies rather than universal sequences.