Impactos de processos de secagem na qualidade do café Arábica (Coffea arabica L.)

Abstract

In the coffee drying process, the use of mechanical dryers has grown in order to reduce quality losses, save time, and increase production efficiency. Fixed-bed dryers offer the lowest acquisition and maintenance costs, allowing for the processing of large volumes. This type of equipment requires strict control of drying parameters such as fruit mass temperature, layer height, airflow, and hot air temperature. In addition to equipment conditions, fruit characteristics also influence drying quality. Thus, after harvesting, the fruits need to be washed and separated into different stages of maturation: cherry coffee fractions (denser and more moisture) and overripe fractions (less dense and less moisture). In this sense, the present work aimed to evaluate the impacts of drying processes on the quality of Arabica coffee (Coffea arabica L.) in fixed-bed dryers with different useful operating volumes (12, 15 and 18 m³) at the cherry and overripe stages of maturation. It identifies potential impacts caused by differences in dryer size and initial moisture content, identifies which parameters directly impact moisture removal behavior, and predicts mathematical models for drying under each condition, assisting producers in deciding on the best drying parameters. This study is divided into three chapters. The first presents a theoretical study based on data obtained from scientific literature, with emphasis on publications indexed in the Elsevier (ScienceDirect), SpringerLink, Web of Science, Wiley Online Library, MDPI, and SciELO databases. It covers the main fundamentals related to the drying of agricultural products, coffee quality and processing, fermentation processes, kinetic modeling, and drying technologies, providing a scientific basis for the research. The second chapter comprises a study that relates different drying volumes and maturation stages to the final beverage quality, through physicochemical and sensory analyses, and evaluates the relationship between quality and the possible occurrence of natural fermentations in drying process. The third chapter presents a mathematical modeling study of the fixed-bed drying process under these same conditions, emphasizing the influence of equipment dimensions on moisture behavior and the prediction of kinetic models that best describe the drying of each volume and maturation stage. This study offers novel contributions to the understanding of mechanical drying behavior at different volumes and maturation stages, suggesting the presence of fermentations in the process and highlighting that the smaller volumes are recommended for obtaining coffees with higher sensory quality, as the height of the fruit layer significantly impacts the moisture removal rate. The Midilli mathematical model best describes the fixed-bed drying data and aids in the reproducibility and predictability of processes. This led to the creation of a decision flowchart to assist producers in determining the ideal drying volume for each stage of maturation and final objective.