Robusta coffee (Coffea canephora) possesses great industrial potential, whereas its intrinsic flavor defects compromise market competitiveness. Honey processing utilizing residual pulp and mucilage is capable of improving green coffee quality; nevertheless, the absence of quantitative research regarding graded pulp retention limits its industrial application. In this study, fermentation experiments with gradient retention of coffee cherry pulp were conducted to clarify the differential regulatory effects of varying coffee cherry pulp-retention amounts on physicochemical properties, functional components and volatile flavor precursor compounds of Hainan Robusta coffee. Quantitative scoring of coffee quality using international standard cup measuring instruments and the grey relational analysis was further employed to comprehensive quality assessment. Compared with the 0% coffee cherry pulp-retention treatment, all other treatments showed higher levels of selected functional components and volatile flavor precursor compounds. The 66% coffee cherry pulp-retention treatment enriched key roasting flavor substrates: sucrose, organic acids, pyrazines, and esters were increased by 8.74%, 26.58%, 80.66% and 30.18%, respectively. Meanwhile this treatment exhibited significantly lower protein and alkaloid contents than the 100% and 33% coffee cherry pulp-retention treatments, and significantly lower flavonoid content than the 0% and 33% coffee cherry pulp-retention treatments. This treatment exhibited remarkably excellent cup scores by 80.35 and superior comprehensive quality, outperforming the other treatments by 6.05–18.51%. This study identifies the optimal coffee cherry pulp-retention ratio for Robusta coffee post-harvest honey processing, providing theoretical basis and feasible technical references for the quality improvement, standardized processing and industrial promotion of local Robusta coffee.

Improper disposal of coffee-processing by-products can cause environmental pollution, greenhouse gas emissions, and resource loss, whereas their reuse in coffee plantations may support sustainable production. This review systematically examines the material properties, stabilization methods, field application pathways, agronomic effects, quality responses, and environmental risks of coffee-pulp-type by-products in cultivation. Relevant studies published up to June 2026 were retrieved from Web of Science, Scopus, ScienceDirect, SpringerLink, Google Scholar, and CNKI and qualitatively synthesized along the soil–plant–quality continuum. Current evidence suggests that properly stabilized materials, applied at appropriate rates, can improve soil organic matter, structure, water and nutrient retention, microbial activity, plant growth, photosynthesis, and crop yield in plantations. They may also indirectly influence green bean quality by regulating sugars, amino acids, chlorogenic acids, and caffeine. However, these effects depend strongly on material properties, maturity, application rate, coffee genotype, soil and climatic conditions, and management practices. Excessive or insufficiently decomposed materials may cause soil acidification, phytotoxicity, oxygen depletion, nutrient imbalance, and yield–quality trade-offs. Overall, recycling within plantations can turn processing waste into farm inputs, reinforce on-farm carbon and nutrient cycles, ease disposal burdens, and advance BCG and wider circular-economy principles in practice.