Optimum hygiene starts during the surface treatment of stainless steel

Stainless steel (SS) is the construction material of choice for production, storage and transportation of ingredients and products in the food industry. The material does not give off any substances that may end up in the final product and is easy to clean. At least if the stainless steel material has undergone  proper surface treatment. A few criteria to watch out for 

Surface roughness < 0.8 micron

EHEDG (European Hygienic Equipment Design Group) suggests that the surface roughness of stainless steel (SS ) coming into contact with foodstuffs should have a Ra value of less than 0.8 micrometer. In some cases even lower roughnesses are required (smoother surfaces), depending on the quality requirements of a particular process.

The polishing tools

With polishing tools such as fat and chalk it is easier to make the surface smooth, but residues of fat or chalk may stay in the microstructures of the surface, leading to risk of contamination. Therefore, polish dry or only with water.

The brush direction

Production and storage tanks are best vertically brushed and pipes in the flow direction. If a tank would be brushed in the horizontal direction, the surface in the vertical direction can be more rough, leading to risk of contamination staying in the tank during emptying.

Passivation

After mechanical brushing and/or polishing, residues remain on the stainless steel surface. The chromium oxide layer on the stainless steel surface, and thus the corrosion resistance, will be affected. A chemical posttreatment with citric acid or nitric acid will re-establish the optimal surface .

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