Product contact surfaces must be finished to a degree of surface roughness that is smooth enough to enable them to be easily cleaned and disinfected. The surface finish must have a roughness area Ra as low as practicable and without cracks, pits or cavities where water or soil might be retained. Although a surface finish Ra < 0.3 pm is a minimum requirement in the pharmaceutical industry, a surface roughness Ra # 0.8 pm is considered as acceptable for the food industry. Surface roughness, Ra, of enclosures in hygienic production areas should not exceed 2.5 pm. As surfaces deteriorate with time, their cleaning becomes more difficult (Hauser et al., 2004a).
The technique used for achieving the appropriate surface finish is of great importance. Although a surface roughness of Ra 0.8 pm can be achieved with different surface finish techniques (glass blasting, ceramic beats blasting, electropolishing, pickling), the topography/structure of the surface can differ a lot, giving different cleaning results.