Systematic literature review on cultivation and post-harvest practices for quality optimisation in sustainable smallholder specialty coffee (2012–2025)

This systematic literature review synthesises research from 2012 to 2025 on cultivation and post-harvest practices for quality optimisation in sustainable smallholder specialty coffee. A total of 102 peer-reviewed studies were analysed across five practice modules-planting/agronomy, post-harvest processing, drying, storage, and micro-roasting. A modified PICO (Population, Intervention, Comparator, Outcome) framework was applied, with population redefined as smallholder-feasible contexts and outcome recast as a three-level adoptability classification, and each study was scored using a composite Synthesis Without Meta-analysis index integrating endpoint coverage, direction of effect, and adoptability. Results reveal a sharp global rise in fermentation-focused research after 2020, with Brazil, Ethiopia, Indonesia, and Thailand emerging as the leading contributors, listed in descending order of publication output. High-Synthesis Without Meta-analysis-score studies identify self-induced anaerobic fermentation (24–72 h ≤ 24 °C), open-greenhouse drying, and hermetic storage (PICS/GrainPro) as the most feasible low-cost interventions that enhance flavour stability and meet specialty standards. Integrating these practices with light-to-medium roasting and simple digital monitoring (e.g., NIR or e-nose) forms a replicable, sustainable production model for smallholders. Overall, the evidence underscores that clean fermentation, efficient solar drying, and hermetic storage-supported by data-driven monitoring-can simultaneously elevate cup quality, reduce post-harvest loss, and strengthen smallholder participation in global specialty coffee value chains. Based on the identified evidence gaps, future research should focus on optimising the fermentation process (e.g., standardising microbial starter cultures) and developing integrated solar-based clean-energy drying systems, to enable smallholder farmers improve process consistency and close the sustainability loop in specialty coffee production.