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Understanding good design pays dividends

07 April 2018

Misaligned flange joints can all encourage soils to accumulate where they may be hard to remove.
Misaligned flange joints can all encourage soils to accumulate where they may be hard to remove.

The design of food-processing and packaging equipment is critical to cost-effective and hygienic operation in food production. But how can the term ‘hygienic’ be interpreted? Eric Partington offers advice. 

Hygienic does not just mean ‘always shiny’. It means ‘resistant to the build-up of process soils and easy to clean between uses’. The Machinery Directive EC 2006/42 requires that ‘machinery intended for use with foodstuffs is designed and constructed in such a way as to avoid any risk of infection, sickness or contagion’. All surfaces in contact with foodstuffs must be smooth and have neither ridges nor crevices which could harbour organic materials. And they must be easy to clean and disinfect, where necessary, after the removal of any easily-dismantled parts.

These design features will also make it quicker and less expensive to clean the plant between production runs and will allow the volumes, concentration and temperature of the cleaning agents – and therefore, also, the volume and concentration of the resultant effluent – to be minimised. So, designing for hygiene can help reduce production costs.

What does ‘hygienic design’ involve and how can it be applied to the design of new equipment? Rough surfaces in contact with a food product will encourage adherence. The European Hygienic Engineering and Design Group (EHEDG) recommends a surface finish (expressed in ‘roughness average’ Ra units) of 0.8µm or lower. To put this into perspective, stainless steel sheet cold-rolled to the commonly-specified 2B finish will have a surface roughness of between 0.1 and 0.5µm Ra. It is also important that the surfaces of any welds with which the food will be in contact are not left rougher than 0.8µm. While this still represents peaks and troughs considerably bigger than a typical micro-organism, but cleaning a metallic surface of 0.8µm Ra is usually straightforward. However, such a surface can deteriorate with time if it is abraded rendering it more difficult to clean. One advantage of stainless steels is that they are more able to resist scratching.

Joints between the component parts of a piece of equipment need particular attention. Misalignment of adjacent parts and unsealed crevices at flange joints can all encourage soils to accumulate in corners and crevices where they may be hard to remove.

Dead arms, pipework equivalents of a cul-de-sac, where probes or sensors may be attached are difficult to flush out during cleaning. A dead arm should not be more than 50% longer than the diameter of its bore. Ensuring that all vessels, pipework, and pumps are self-draining will preclude cross-contamination between batches. But how do we know if a piece of equipment or a complex section of plant pipework is hygienic? Many component items available on the European market have been specifically tested and certified by EHEDG and carry a logo to say so. But any piece of equipment can be submitted for assessment by an organisation such as Campden BRI.

But what of older plant, which may not have been designed to meet the 2006 Machinery Directive? The food business operator’s responsibility under the Food Hygiene Regulations to ‘ensure the fitness [of his food products] for human consumption’ does not mean that the equipment should no longer be used. However, if there is any reason to suspect that it may not be possible to sanitise the equipment completely between production runs under the established cleaning regime, it would be ‘duly diligent’ to consider modifying that procedure until it can achieve the required cleanliness.

Hygiene is not optional. But designing for it can also pay dividends. An appreciation of what can contribute positively towards hygiene can help to more precisely structure food safety management systems.

Eric Partington is chairman of UK and Ireland Regional Section of EHEDG.


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