Volcanic fermentation is an innovative technique in post-harvest coffee processing that involves forming conical mounds, called “volcanoes”, to create specific biotransformation conditions. This study investigates the impact of different volcano fermentation methods on the chemical composition and sensory attributes of coffee. Four methods were evaluated: asphalt patio (E1), on pallets (E2), in steel containers under the sun (E3), and in steel containers in the shade (E4). The chemical composition was analyzed in terms of sugars (sucrose, glucose, fructose), organic acids (citric, malic, succinic, lactic, acetic) and alcohols (glycerol, ethanol). In addition, color differences (ΔE) and sensory analysis of the fermented coffees were evaluated. The results of this study reveal that volcanic fermentation produces high-quality specialty coffees, but with divergent profiles of acids and alcohols, thus influencing the sensory characteristics of the resulting beverage. However, the different methods of volcanic fermentation did not significantly affect pH and soluble solids, indicating that the microbiota developed an efficient and consistent fermentation regardless of the solar exposure conditions. The most frequently mentioned sensory descriptors were chocolate, citrus fruits, honey/molasses, caramel, floral, and brown sugar. These findings highlight the significant influence of the volcanic fermentation method on the chemical and sensory quality of coffee fermented.

Tumbling ball mills are a common comminution device in the mineral industry processing, wherein the particle size reduction is performed by action of the grinding media. Different forms of transverse motion in a rotating cylinder have been studied by many researchers. The aim of this paper was to study the transitional phenomena between cascading, cataracting and centrifuging motion. In order to observe these transitions, experiments were carried out in a tumbling mill of 300 mm diameter, and three sizes of chrome steel balls were used as grinding media. Each size of ball was employed in three different lengths of the mill with the purpose to investigate the end-walls effect in the behavior ball charge. The image analysis technique was employed to identify the transition regions. A high-speed camera with maximum speed of 2000 frames/s was used to record images. Experimental data showed it was not found the end-wall effects on the transitional behavior, and this effect can be assessed in numerical studies by analyze of the specularity coefficient.