Evaluation of traditional and modern drying methods for coffee husk processing: Physical characteristics and quality standards

Abstract

Coffee husk is a major by-product of coffee processing in Indonesia, with great potential for value-added utilization. However, its high moisture content and susceptibility to spoilage necessitate effective drying methods to ensure quality and stability. This study investigated the effects of sun-drying, batch-dryer, and cabinet-dryer methods on the physical characteristics of coffee husks from Arabica and Robusta varieties. Moisture content, color parameters (L, a, b, ΔE, chroma, hue), and bulk density were evaluated. Results showed that the batch-dryer method consistently reduced moisture content below the 12% standard, while maintaining color stability. The cabinet-dryer produced more uniform color, although with lower chroma due to browning, while sun-drying led to unstable moisture content and greater color change. Bulk density varied significantly, with Robusta showing higher values, especially with sun-drying and batch-dryer methods. ANOVA revealed significant differences between drying methods for all parameters, with further Duncan tests confirming the superiority of batch-dryer in ensuring coffee husk quality. These findings highlight the importance of artificial drying methods, particularly batch-dryer, in producing coffee husks with optimal physical characteristics for downstream processing into value-added products such as flour. The impact of this study is to provide a scientific basis for developing more effective postharvest technologies and to promote the utilization of coffee husks as an economically valuable raw material, thereby supporting waste reduction and sustainability in the coffee sector.