The European Hygienic Engineering & Design Group (EHEDG) is a consortium of equipment manufacturers, food companies, research institutes and public health authorities who have formed in order to promote hygiene during the processing and packing of food products.
The group has published guidelines by which the food industry can act to ensure compliance with regulations that legislate the handling, preparation, processing and packaging of food – for example EC Directives 98/37/EC and 93/43/EEC.
The EU has mandated that the European Federation of Standardisation Institutes (CEN) produces the standards by which companies must comply. The EHEDG guidelines feed into these standards and as such are not legal guidelines but are seen as ‘best practice’ in the food industry.
Keeping food hygienic
Historically, preventative measures were not employed for microbial contamination of food during the processing cycle. Instead, the focus lay on the removal of microorganisms after processing, for example by the application of heat, or the control of oxygen and carbon dioxide concentrations and the removal of the nutrients needed for microbial growth.
Industry developments, coupled with the publication of the EHEDG guidelines, have seen a shift towards preventative rather than reactive hygiene measures. The guidelines address a whole spectrum of issues ranging from the hygienic packing of food products to guidelines on the handling of air in the food industry, all of which focus on preventing contamination in the first place.
The EHEDG guidelines reflect the need for components of food processing equipment to comply with hygiene standards. The guidelines now provide best practice by which equipment can be designed – even down to the component level – in order to be considered hygienic. The aim is to provide qualified engineers, who are designing equipment for food processing and who also need to or want to comply, with hygienic engineering the means to design/develop an instrument that prevents contamination.
Hygienic design
One of the fundamentals in the prevention of contamination is the concept of hygienic design. This is the term for the design of equipment and machinery that is in practical terms ‘easy-to-clean’. As this definition may leave too much room for interpretation, the EHEDG has published guidelines and recommendations on equipment design. It also offers the service to inspect and assess equipment in order to approve that specific instrumentation fulfils the design recommendations and can therefore be called hygienic.
Historically, when components of food processing instruments have been developed - for example load cells in process vessel scales – the focus has been clearly on the technical specifications rather than on hygiene.
While on all equipment that is in direct contact with food or food products there are now very clear standards to follow and equipment compliance can even be certified, the area that is not in direct contact with food has been neglected. Actually for non-contact equipment no agreed standards exist. Even so, it is widely accepted that the area that is also not in direct contact with the product needs to be clean to reduce contamination risk.
Load cells, for example, do not come into direct contact with products in automatic mixing and batching equipment. However, it is essential to counter creeping contamination and the resultant spreading of germs. So, components are now being developed that are both hygienic and also provide the necessary technical solutions. This means that the principles for hygienic design are being employed on all equipment in the direct vicinity of food processing equipment. Hence similar rules to those which cover contacting equipment need to be applied.
An example: the hygienic load cell
In order to comply with the EHEDG guidelines, the housing of the load cell should be made completely of stainless steel alloy 1.4404 in accordance with AISI316L and thus meet the requirements for corrosion resistance, mechanical stability and non-toxicity of components in contact with the product.
The material must demonstrate particularly high corrosion resistance even in the case of exposure to solutions containing chloride, dependant on concentration and temperature. For functional reasons, making the measuring element out of highly stable, rustproof martensitic chromium steel would add an additional technical benefit.
The use of plastics should only be limited for cable sheathing. The thermoplastic elastomer (TPE) used should have high resistance to cleaning agents and processes and should feature excellent long-term resistance compared with PVC.
The complete housing should have smooth, stainless steel surfaces that are non-absorbent and free from imperfections such as holes, grooves and gaps. An even surface structure with low surface roughness of less than 1µm is needed to provide optimum cleanability.
By developing a hygienic load cell in coordination with the EHEDG guidelines, other features also need to be taken into account. These include:
- Welded joints – the micro-plasma welding process used should produce clean, smooth, welded joints with no roughness on which dirt may collect or become engrained. This would ensure the welded joints do not impair cleanability.
- Rounded corners – all corners should be rounded and not feature sharp edges. The adjustment chamber, for example, should be welded at the corners to ensure that sharp edges are avoided.
- Self-draining – there should be no horizontal surfaces on any part of the housing. The upper section of the housing should have an inclined surface to enable water to flow freely away. The adjustment chamber should also be rounded to prevent water from remaining on the surface.
- All mounting kits and accessories need to follow the same high standards as detailed above, avoiding gaps, open threads, and unsealed metal-to-metal contact surfaces.
Sartorius, the weighing specialist based in Germany has recently developed the PR6202, the only hygienic load cell currently on the market that is strictly designed to meet the stringent requirements of the EHEDG guidelines (Fig.1).
The Technical University of Munich's Chair for Mechanical Engineering and Process Technology has concluded in its overall assessment that Sartorius’ PR6202 load cell is designed hygienically in accordance with the recommendations of the EHEDG.
In addition, it has also established that, for the most part, despite surfaces that do not come into contact with product they even meet the requirements for areas that do come into such contact. Sartorius, and in specific, the PR6202 hygienic load cell, sets new standards for load cells in the food industry and sectors with similarly high requirements for cleanability and reliability.
Eugen Gassmass is with Sartorius Hamburg, GmbH, Germany. www.sartorius.com. For more information, visit www.ehedg.org and www.hygienic-design.com
