‘Feeding the Planet, Energy for Life,’ is the main topic of the EXPO 2015 that will be held in Milan, Italy this year. The Universal Exposition is a meeting place for the food and other industry players and will kick off in a couple of months. In processing food, hygiene is a very important topic and exactly for this reason, stainless steel has turned out to be the best material to use. However, not just any stainless steel will do the job. The right surface finish is essential, and to make a good choice, the certification of materials for the food processing plants forms a key aspect that is gaining attention.
Surface finish and hygiene
B720 Arquitectos, led by Fermín Vázquez,
has designed the Spanish Pavilion for Expo
Milano 2015. Source: Milan Expo Tours
At the Expo Milano 2015 two interconnected aspects of food production will be at the centre of attention: traditional cultural values and the use of new technologies. Stainless steels are widely used in the food and beverage processing and manufacturing industries, for example for bulk storage and transportation, as well as in preparation and presentation.
The food processing and catering industries are among the largest consumers of stainless steel worldwide and ‘cleanability’ as well as corrosion resistance of the material is essential. With regard to this, it is important to understand the influence of surface finish. Poor corrosion performance for example is almost always linked to a poor choice in surface finish. When hygiene is essential, like in the food industry, an ultra-smooth surface is ideal. To determine ‘smoothness’, it is the ‘roughness’ that counts: the lower the surface roughness, the better the material is suited for use in environments where hygiene is top priority.
A generic description like ‘satin polished’ isn’t sufficient in determining which surface finish is the most hygienic. The surface roughness should be described by means of Ra, that expresses an average measure of the texture of the surface, normally in micrometres. Depending on the grade of stainless steel selected, it will be suitable for most classes of food and beverage products. In the food processing industry the '316' grades (1.4401/1.4404) are unofficially known as the 'food' grades, however, depending on the precise application of the material, the 1.4301 and 1.4016 grades may also be used.
Most important is that the material has a Ra of max 0.8 micron for cleanability, or preferably even a Ra of max 0.5 micron, so that corrosion resistance is also assured. The lower the surface roughness, the better, since corrosive material and bacteria are less likely to stick to a very smooth surface. Additionally, the smoother the surface, the easier it is to clean it.
Certificated hygienic metal
In order to promote hygiene during the processing and packing of food products, the European Hygienic Engineering & Design Group (EHEDG), a consortium of equipment manufacturers, food industries, research institutes, and public health authorities, established guidelines for materials and provides a certification when these are met.
Last year, the Italian Marcegaglia was the first steel manufacturing company to receive a certification from the EHEDG. Both the pickled and the bright annealed surfaced steels that Marcegaglia manufactures were tested, and Marcegaglia’s stainless steel tubes for food & beverage applications were classified as ‘easy cleanable’. In the article on Marcegaglia in Stainless Steel World News the EHEDG stated that “equipment for food processing should be designed according to specific hygienic guidelines and that this is fundamental in order to prevent contamination from micro-organisms”.
Stainless steel is the preferred metal for use in the food processing and catering industry. By choosing the right surface finish, hygienic use is assured. Surface roughness affects corrosion and to grasp the importance of this on a micro scale, the Ra value, or roughness value can be used.