A roasting drum has a main body and at least one opening formed through the main body. The main body has a first end, a second end opposite the first end, and multiple drums. The multiple drums are mounted around one another in sequence, are fastened to one another, and communicate with one another. Each one of the multiple drums has a blending blade formed on an inner surface of the drum. The blending blade is spiral and extends from the first end toward the second end. The blending blade of one of the multiple drums twists along a clockwise direction from the first end toward the second end. The blending blade of another one of the multiple drums that is mounted around the drum twists along a counter-clockwise direction from the first end toward the second end.