Grading involves separating food products into categories based on various quality factors such as size, shape, color, and presence of defects. It can be done manually or mechanically. Manual grading involves trained workers visually inspecting and sorting products. Mechanical grading uses machines like screens, roller graders, diverging belt graders, and weight graders to separate products. Screen graders use perforated screens to sort by size, roller and belt graders gradually increase space to drop smaller products first, and weight graders index products by weight. Potato graders use expanding pitch rubber spools or self-propelled combines to grade and harvest potatoes with minimal damage.