Size reduction is the mechanical process of breaking food particles into smaller pieces by crushing, grinding, cutting, or milling. It is one of the most fundamental operations in food processing: wheat is milled to flour, cocoa nibs are ground to liquor, meat is minced, vegetables are diced. Reducing size increases surface area, which speeds drying, extraction, cooking, and digestion, and it creates the textures consumers expect, from fine flour to coarse kibble. The equipment ranges from hammer mills and roller mills to colloid mills and homogenisers, each chosen for the target particle size and the product’s sensitivity to heat and shear. Control of particle size distribution is a quality parameter in its own right, deciding mouthfeel and functionality.