August 15, 2015
The Ethiopian famine was in the minds of many when the first issue of Nickel magazine appeared in 1985. It featured a story on how nickel-containing stainless steels were playing a significant role in food safety as well as reducing the wastage of food that occurs between the farmer and the consumer.
Today, the food supply chain is even more internationalised and many countries have adopted food safety standards similar to those successfully employed in both Europe and North America. Those standards have gone through significant advances in the last 30 years and will continue to improve. But those same nickel-containing stainless steel alloys have remained and will remain as the first choice for food contact surfaces for all food and beverage processing operations.
Keeping food safe is a challenge. It requires not only selecting
the appropriate materials and proper equipment design but a rigorously enforced system to keep out dangerous contaminants.
One of the more recent standard improvements is the definition of a product contact surface. It is not restricted to the obvious surfaces of the containers, conveyors and vessels on or in which food is processed or stored, but includes any surface from which contamination, whether deposited on the surface or a constituent of the material, could drip, splash or be blown onto the food. Moreover, these surfaces must all be hygienic. This does not just mean “always clean and shiny”, reassuring as that may be, but resistant to contamination and easily cleanable between uses.
Enter the nickel-containing stainless steels, the most common alloys being Type 304 (UNS S30400), 304L (S30403) and 316L (S31603). Their corrosion resistance based on chromium and enhanced by nickel, is universally recognised: there is a stainless steel suitable for every food product from milk to mustard to the most demanding liquids such as soy sauce, where 6% Mo alloys are required. And sometimes the disinfecting chemicals are more corrosive than the food products themselves.
To allow for proper cleaning and disinfection, food product contact surfaces, must be smooth. Both EHEDG (European Hygienic Engineering and Design Group) and 3-A Sanitary Standards (U.S.) recommend smoother surfaces than 30 years ago, and now call for a surface roughness of 0.8µm or less. This standard can be exceeded by a 2B finish on stainless steel sheet. A high quality no.4 polished finish will also meet that requirement. In addition, the hardness of stainless steel resists the abrasion (for instance from dry particulate foods) which can roughen a food contact surface to the point where biofilms can adhere so firmly to the surface that normal cleaning procedures cannot remove them.
Outside Europe and North America, Australia, New Zealand and Japan have had rigorous standards for many years now and China is also upgrading its standards to world-class. The common element for all these countries is nickel-containing stainless steels as the materials of choice.