After coming out of the polishing machine, green coffee beans often still contain impurities such as whole cherries, broken beans, and black beans. The beans are uneven in size, so classification is necessary to meet the quality standards required for commercial coffee.
Size Classification: This step separates beans by size—large, small, fragments, and impurities—to create uniformity in the bean mass. This helps the next classification by weight to be more accurate and efficient, improving overall productivity. Size sorting can be done using sieving machines or manual sieves.
Density (Weight) Classification: This process separates beans by specific gravity, removing lighter materials and impurities to prepare for color sorting with greater accuracy and efficiency. It is essential to conduct size classification first before weight sorting to ensure machine precision.
Equipment such as air blowers (catado), suction fans, or manual vibrating sieves can be used for density separation.
Color Classification: Also known as grading based on national quality standards. This can be performed using color-sorting machines or manually by visual inspection on conveyor belts or sorting tables.
Color sorting ensures uniformity in color, removing defective or discolored beans to meet standard quality criteria.
Economic and technical considerations should be calculated to choose the simplest and most cost-effective methods before production, ensuring consistent product quality at the factory level.
After grading and classification, coffee beans must undergo quality inspection to confirm they meet required standards before storage or export.