Effect of Broken Coffee Beans Particle Size, Roasting Temperature, and Roasting Time on Quality of Coffee Beverage

Abstract

Optimum flavor and aroma of the coffee are developed during the roasting process. However, certain problems exist in the coffee roasting process such as partial charring, over roasting, and poor temperature distribution across the coffee bean (due to the low thermal conductivity of bean), if conditions are not optimized. Hence, uniform temperature distribution across the coffee bean in the roasting process is highly desirable. To achieve these requirements, the broken coffee beans were positioned in a single layer packed bed arrangement using the closed system by circulating hot air. In this experiment, three factors were arranged in a completely randomized design with three levels and three replications. The first factor considered was roasting temperature (200°C, 230°C, and 260°C), second factor was roasting time (5 min, 10 min, and 15 min), and third was particle size (4–6 mm, 2.36–3.35 mm, and 1.7–2.36 mm). The initial moisture content of raw beans (cv. Limu) was determined. The data were collected on selective physical properties of roasted coffee beans and sensory acceptability of prepared beverage. The results showed that the physical properties and sensory acceptability are significantly high ( $P<0.001$ ). It depends on the interaction effect of all the studied factors. Among the studies parameters, roasting temperature of 230°C with a particle size range of 4–6 mm showed the steady transition in dry mass loss and change in bulk density with increase in roasting duration. Coffee roasted at 230°C for 10 min with a particle size of 4–6 mm showed the highest sensory acceptability score (89.21). In conclusion, it can be said that a temperature of 230°C, a time of 10 min, and a particle size between 2.36–3.35 mm and 4–6 mm are recommended conditions for the roasting process of coffee beans.