For food contact surfaces the finish is a hygiene specification, not a decorative one. The requirement is a smooth, uniform, cleanable surface with no crevices where product or bacteria can collect. In practice that means a well-controlled No.4.
Why No.4 and not mirror
A mirror finish looks cleaner but shows every scratch and water mark, and any surface damage from cleaning is immediately visible. No.4 is the standard food-industry finish because it stays acceptable looking after years of aggressive cleaning, and the fine directional grain is easy to re-work in place.
What matters in production
- Uniform grain — inconsistent roughness means inconsistent cleanability
- Wet grinding — keeps the surface cool and avoids embedded abrasive and burn marks
- Full removal of grinding residue — residue left on the surface is a contamination risk
Recommended machines
- Sheet grinding machines — wet grinding for No.4
- Sheet polishing machines — final refinement
- Coil grinding lines — for continuous coil feed