Effects of Roasting Degree and Grinding Size on Caffeine Content and Sensorial Quality of Coffee

This study optimized roasting and grinding parameters for Ethiopian Arabica coffee ( Coffea arabica L.) to enhance caffeine content and sensory attributes using Response Surface Methodology (RSM) with Box–Behnken design (BBD). Green coffee beans from Kercha Woreda, West Guji Zone, Oromiya, Ethiopia, were roasted at 200, 212.5, and 225°C for 7, 9.5, and 12 min, corresponding to light, medium, and dark roasts, respectively, then ground to 800, 450, and 100 μm (fines < 100 μm), and analyzed for caffeine via high‐performance liquid chromatography (HPLC) and sensory attributes using Specialty Coffee Association (SCA) cupping protocols. Caffeine content ranged from 1.30 to 1.53 g/100 g, with finer grinds and lighter roasts yielding higher levels due to reduced thermal degradation and increased extraction efficiency. Sensory scores varied from 66% to 88%, with medium roasts (212.5°C, 9.5 min) and coarse grinds (800 μm) achieving the highest scores due to balanced aroma, sweetness, and uniformity. RSM‐BBD identified optimal conditions of 11.8249 min at 213.347°C, with a size 793.972 μm grind, yielding 1.35 ± 0.01 g/100 g caffeine and 87 ± 0.02% cupping score, validated through triplicate trials. ANOVA confirmed significant effects of roasting time, temperature, and grind size on both responses ( p < 0.05). These findings provide a framework for consistent coffee quality, offering insights for producers to tailor caffeine and sensory profiles for diverse brewing methods.