The present disclosure describes a refiner plate segment with one or more continuous, generally spiraling transition zones. A transition zone spans from an area near the inner portion of the plate, near the breaker bar area, and extends toward an area near the periphery of the plate at an angle. A tangent line to the transition zone intersecting a radial line forms this angle. The radial line is formed by a line perpendicular to the outer periphery passing through the center point of the center of plate rotation.