Abstract
Controlling operating parameters during the drying process plays a crucial role in determining changes in the physical properties of coffee beans. This study examined the combined effect of drying temperature and cylinder rotation speed on the density and porosity of coffee beans in a rotary dryer system. Temperature variations were set at 40°C, 50°C, 60°C, and 70°C, while rotation speeds were varied by 5 rpm, 8 rpm, and 12 rpm. The evaluation was conducted to identify trends in changes in the internal structure of the beans in response to heat intensity and mechanical forces during the process. The results showed that increasing temperature contributed predominantly to the decrease in density, which was related to a reduction in water content and changes in the distribution of interparticle space within the bean matrix. At the same time, increasing rotation speed increased the opportunity for contact and movement between beans, thus accelerating the release of water vapor from the interior of the material. These conditions resulted in increased porosity values, especially at a combination of high temperature and 12 rpm rotation. Conversely, low temperature with 5 rpm rotation tended to maintain a higher structural density. The interaction of these two variables indicates that heat transfer and mechanical dynamics occur simultaneously in shaping the final physical characteristics of the product. In general, proper temperature and rotation speed settings are key factors in achieving stable and uniform drying results. These findings provide a technical basis for optimizing the rotary dryer-based coffee bean drying process.