Stainless steel finishes are an important aspect in sanitary food processing equipment, as finishing options alter more than just the appearance of the metal.
A variety of methods are used to achieve stainless steel finishes — hot and cold rolling, grinding with abrasives, buffing with cloth wheels, tumbling, dry etching, sandblasting, acid solutions, bead blasting, and more — each one affecting the surface smoothness in varying degrees.
According to the International Association for Food Protection, surface roughness has been generally related to cleanability of stainless steel, with smoother surfaces often considered more cleanable.
In a sanitary application, such as food processing, stainless steel needs a smooth, scratch-free, and non-corrosive finish to prevent the harboring and growth of bacteria.
Know the Terms
In choosing the type of finish needed for your application, it is important to understand the terms and definitions used for stainless steel finishes.
Surface Texture
The surface of the material including irregularities and deviations, including roughness and grain.
Grit
Grit is defined as the size of the abrasive used in the polishing process. Typically coarse, lower grit numbers are associated with grinding and higher grit numbers are associated with polishing. Grit size however does not fully define the surface.
RA (Roughness Average)
A standard for an average of the peaks and valleys of the metal’s surface, measured in microinches or micrometers. A profilometer is used to determine RA values.
RMS (Root Mean Square)
A machining standard used to diagnose machine operations and surface finish.
Stainless Steel Finishes for Food Processing
When it comes to applying stainless steel finishes in the food processing industry, we have found customers prefer these five finishes the most.
| Mill Finish | 2B Finish | No. 4 Finish | No. 4A Finish | Bead Blast |
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| Description | Unfinished steel in basic supply condition. | Achieved by cold-rolling, heat-treating, and pickling. A final light rolling pass gives the surface a smooth, reflective gray sheen. It is the standard finish for 304, 304L, and 316 stainless steel. | Consistent straight grain finish. It is produced by polishing with a 180-240 grit belt. | Fine polishing grit lines that are uniform and directional in appearance. It is produced by polishing with a 180-240 grit belt. | Uniform, non-directional, low-reflective surfaces that contrast well with high polished finishes. It is accomplished by applying fine glass beads at a high pressure without damaging the surface. |
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| Applications | Structural | Material handling, processing, direct food contact | Clean rooms, food processing equipment | Clean rooms, food processing equipment, Pharmaceutical, 3A Dairy Standards | Structural, material handling, food handling |
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| Sanitation Environment | Not used in food contact areas | Suitable for sanitary wash down procedures | Suitable for sanitary wash down procedures | Suitable for sanitary wash down procedures | Suitable for sanitary wash down procedures |
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| RA | >100 | 36 (7 gauge) 15 (16 gauge) | 29-40 | 18-31 | 45 |
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*The images in this post are a portrayal of the finish and are not completely accurate representations. Screen resolution, picture size, and photo quality all affect the look of the finish in the picture.
The Best Finish
Stainless steel resists corrosion, maintain strength at high temperatures, and is easily maintained — making it ideal for the food processing and pharmaceutical industries. Top it off with one of the 4 finishes above (not mill, unless the application is only structural in a non-food area!) and you’ll have an easy to clean surface that keeps your food product safe.
