The surface of stainless steel resists oxidation at high temperatures and it tolerates very low temperatures as well. Its lightweight quality and high durability allow the development of endless applications in myriad industries. Stainless steel paved the way for modern technology and continues to be essential in our everyday lives.
Article by Ivan C. Amaya, Belt Technologies, Inc.
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Historical overview
The advantages of metal over other materials in terms of safety, strength, and sanitation have been well documented since Philip Monarz published the first detailed work on the corrosion resistance of stainless steel in 1911. In 1912, Eduard Maurer and Benno Strauss—two specialists working for the Krupp Iron Works in Germany—patented the first austenitic stainless steel of 21% chromium and 7% nickel. This was then followed by Harry Brearly’s patent of the first martensitic stainless steel in 1913. Other patents and combinations soon followed. It has been said that “stainless steel, with its sleek, shiny surface and tremendous strength, is a marvel of technology. It has revolutionized most modern industries, including food, medicine and transportation” (ii).
Antibacterial properties
Research-based literature and several extensive studies have been written on the attachment ability of certain bacteria, such as Salmonella and Listeria, to the surface of different materials including stainless steel, plastic and rubber. Not surprisingly, studies reveal that, “in general, polymeric materials have a stronger affinity for Listeria and Salmonella cells”
(vii). Salmonella and Listeria attach in higher numbers to hydrophobic materials such as rubber and plastic
(iv). Higher numbers of Salmonella and Listeria monocytogenes attach to polymeric materials than to stainless steel materials. Midelet and Carpentier reported similar findings for L. monocytogenes and also that it has a weaker affinity to stainless steel than to plastic materials.
Another study shows that Listeria biofilm formation is significantly higher on polymeric materials than on stainless steel (vii). There have been documented cases in recent years of foodborne illness outbreaks linked to the maintenance and cleaning of processing equipment that includes conveyor belts. As a result of scientific and legal requirements enacted by the FDA (i) food equipment manufacturers should focus their attention on the ability to thoroughly clean and sanitize conveyor belts and other food-related equipment in order to minimize downtime (i). This clearly supports the use of stainless steel conveyor belts as opposed to plasticmade conveyors and even metal-mesh
conveyors.
Stainless steel conveyor belts provide a nonporous surface that can be heated to over 121°C (250°F) for sterilization—well above the temperatures bacteria can survive— while most plastic conveyor belts cannot withstand more than 100°C (212°F). The surface hardness of stainless steel is greater than the surface hardness of polymer materials, and as Midelet and Carpentier (2002) and Tolvanen et al. (2007) reported, the attachment of L. monocytogenes to stainless steel is considerably weaker than it is to plastic materials. As the Tolvanen study concludes, “stainless steel shows weaker adhesion for bacteria and can be considered as the better type of conveyor belt to minimize cross-contamination. Similarly, cleaning is more efficient on hard surfaces such as stainless steel than on soft materials such as plastic.”
Solid endless stainless belt vs. metal-mesh conveyors
The FDA has recently conducted several inspections of food manufacturing plants. A recent FDA warning letter to a food manufacturing facility clearly stated that, as required by 21 CFR 110.80(b)(8), “you must take effective measures to protect against the inclusion of metal or other extraneous material in food” (i).
The warning letter describes in detail that “the mesh-belt conveyor . . . was seen broken or missing pieces in several places. The shape and size of the missing pieces of mesh-belt conveyor material is consistent with reported customer complaints. . . . Your firm’s forensic reports on four of these complaints documented the measurement of the metal fragments to be over 7mm in length”
(i). The FDA report suggests that, in order to avoid the above mentioned problems, metal detectors should be installed and additional employee training must be implemented. It also notes that: “The type and orientation of the metal object in the food affects the ability of the equipment to detect it.
Processing factors may also affect the conductivity of the product and create an interference that may mask metal inclusion unless the detector is properly calibrated. . . . Visual equipment checks may also be used in your process for protection of metal inclusion in product. Monitoring your equipment (meshbelt conveyors, nuts/bolts, equipment with metal to metal contact) to ensure parts are present and secure should be conducted with adequate frequency “(i).
The letter touches on the relevant aspects of appropriate cleaning and sanitizing as required by 21 CFR 110.80(b)(1). It says that: “The conveyor belt from cooling to packaging [was] embedded or stained with food debris after completion of your cleaning procedures. . . . Harmful microorganisms may remain viable on improperly cleaned and sanitized food contact surfaces, equipment and utensils and may lead to contamination of the food products with which they come in contact” (i).
Observations
Very clearly, there are significant advantages to using endless stainless steel belts vs. metal-mesh conveyors; as shown in the above example, the latter conveyors have many moving parts that are likely to wear out and fall off into the food being processed. This scenario does not occur when using endless stainless steel belts, as they do not have any moving parts that come into contact with the food products being conveyed.
Solid stainless steel conveyor belts are easy to operate and sanitize. They are cost-effective when factored against the price of additional equipment (detectors) and the necessary employee training and maintenance required with other belt materials. Endless stainless steel belts do not require any additional equipment or costly training and offer perfect compliance with the existing FDA regulations.
Most importantly for food applications, endless stainless steel belts can be cleaned in place, significantly reducing downtime, labor and the expenses for removal, washing and reinstallation of the conveyor belts. Mesh conveyors, however, have thousands of moving parts, joints and crevices that can house bacteria and prove difficult to clean or drain with standard cleaning agents. Both plastic and mesh conveyor belts must be occasionally removed for immersion in chemical solutions or for the installation of special cleaning systems and brushes that can access hinge points, joints and sprockets for thorough cleaning and sanitation. Endless stainless steel belts have a hard, bacteria-resistant, low-rugosity surface without moving parts, joints or crevices that could harbor bacteria. Sanitizing an endless stainless steel belt does not require the removal of the belt; they can be cleaned in place, with lower-cost detergents and processes.
Last but not least, endless steel conveyor belts are compliant with FDA regulations; this helps users avoid costly and cumbersome legal liabilities associated with non-compliance.
General conclusions
The above demonstrate the advantages and benefits of endless stainless steel belts from both a scientific point of view and a practical, legal and manufacturerminded point of view. The combined effect of a superior, bacteria-resistant material such as stainless steel in the form of a high-quality, specialized endless conveyor belt ensures obvious advantages and a low-cost, high-benefit ratio that does not require additional equipment, training or supervision. These benefits, combined with perfect legal compliance with existing laws, make endless stainless steel belts the most sensible option for food manufacturers.
References
(i)
Almogela, Darlene B. “Inspections, Compliance, Enforcement, and Criminal Investigations” Public Health Service Food and Drug Administration, 4 Mar. 2014. Web. 17 Mar. 2016.
(ii)
General Article: Stainless Steel. Dir. Thomas Ott. American Experience: Stainless Steel. PBS, 2012. Web. 22 Mar. 2016.
(iii)
Midelet, Graziella, and Brigitte Carpentier. “Transfer of Microorganisms, Including Listeria Monocytogenes, from Various Materials to Beef.” Applied Environmental Microbiology 68.8 (2002): 4015-024. Applied and Environmental Microbiology. American Society for Microbiology. Web. 17 Mar. 2016.
(iv)
Sinde, E., and J. Carballo. “Web of Science [v.5.21] – Web of Science Core Collection Full Record.” Food Microbiology 17.4 (2000): 439-47.Web of Science [v.5.21] – Web of Science Core Collection Full Record. 2000. Web. 22 Mar. 2016.
(v)
Tolvanen, Riina, Janne Lunden, Hannu Korkeala, and Gun Wirtanen. “Ultrasonic Cleaning of Conveyor Belt Materials Using Listeria Monocytogenes as a Model Organism.” Journal of Food Protection 3.70 (2007): 758-61. ResearchGate. Web. 22 Mar. 2016.
(vi)
Veluz, GA, S. Pitchiah, and CZ Alvarado. “Attachment of Salmonella Serovars and Listeria Monocytogenes to Stainless Steel and Plastic Conveyor Belts.” Poultry Science 91.8 (2004-2010): n. pag. Oxford Journals. 2 May 2012. Web.
About the Author
Ivan C. Amaya is Belt Technologies’ Sales & Marketing Manager/Americas, with over 20 years of experience in capital equipment, and diverse national and international industrial issues. Belt Technologies, Inc. has been producing custom metal belt conveyor solutions for new and existing conveyor systems for more than five decades. To learn more visit
www.belttechnologies.com.
