In its simplest form, hygienic principles apply to two fundamental aspects of design: surfaces designed for contact with food products, and those not meant to be (non-contact). In general, surfaces meant to be in contact with food must be non-porous, smooth and impervious without cracks or crevices.
Materials should be non-conducive to contamination, meaning non-reactive to food products, corrosive resistant, non-toxic, and durable. In addition, material should not require upkeep maintenance and be easily cleaned: this requires metal surfaces that won’t flake, bubble, chip or otherwise degrade under plant conditions.
As a result, stainless steel is a common and preferred material choice by many OEMs. Metals such as titanium and platinum, while corrosion-resistant and long-lasting, are less prevalent due primarily to cost, however they are a common component in stainless steel alloys for machines designed to work with highly acidic foods. Aluminum is often used for food processing machinery due to its price and lightweight characteristics, but it’s highly susceptible to corrosion, and oxidizing cleaning products accelerate that decline. In some instances plastic coatings are used to help protect against this, but the standard practice is anodizing or hard anodizing aluminum components.
When it comes to material surfaces (generally speaking) the rougher a surface, the more cleaning time required – hence the prerequisite for easily cleanable, smooth surfaces. The metric most used to gauge surface roughness is expressed in µm, as Ra-value described in ASME B46.1. Simply put, Ra is the average of a set of individual measurements of a surface’s peaks and valleys. Both 3-A and EHEDG standards specify that food contact surfaces have a maximum roughness of Ra = 0.8 µm; in practice cold-rolled stainless-steel sheet material usually has a Ra-value between 0.2 and 0.5 µm.
Surface finish quality should deter biofilm formation, however rougher surfaces may be acceptable if it can be shown that clean-ability standards can still be met and all film removal accomplished through cleaning procedures. Nonetheless, surface finishes that were acceptable in recent years are being increasingly questioned because they can hold biofilm – web-like coatings including bacteria which are particularly resistant to sanitation and create a microorganism growth medium.
Other important aspects of machine design include elimination or minimization of crevices, sharp corners, protrusions and shadow zones – not just when new, but over the equipment’s entire lifetime. This concept applies not only to a machine itself, but to the entire solution. For example, problems can arise when equipment parts are mounted together, resulting in non-welded metal-to-metal contact, which in turn can result in narrow and deep crevices. In cases where creating a crevice is unavoidable, cleaning procedures may require instructions for partial or total dismantling of equipment, or for increased cleaning times.
An additional aspect of fit and finish are seals between machine components. Elastomers are often used to seal between metal components, with the caveat that they must be designed and mounted in such a way as to avoid excessive compression, which can destroy the elastomer and increase contamination risk. Another consideration is the use of screw threads and bolts in the product contact area which introduces risk, as do designs that incorporate sharp corners. Dead areas or shadow zones are areas “hidden” from the main flow of cleaning liquids, making them more difficult to clean.
Drain-ability and placement
When it comes to cleaning, equipment “drain-ability” is a key design consideration, since even when no chemicals are used, many microorganisms can easily grow in residual water. Surfaces should be designed to slope toward drain points rather than be completely horizontal, and ridges or ledges that hamper drainage should be avoided. If any of these situations are unavoidable design issues, or if cleaning and disinfectant residues cannot be easily removed thru drainage, specific cleaning procedures need to take such areas into account. Ensuring that all areas are mechanically cleanable, and the equipment is designed in a way that caustic foams and sanitizing solutions can be applied without damaging the equipment is important.
When evaluating a machine’s hygienic design, also consider the actual placement of equipment components such as electronic cabinets, pumps, drives, etc. For instance, a design that places electrical/ PLC components so as to lessen the risks associated with wash down can significantly improve component longevity. In non-wash down environments, the ability to remove or break down parts quickly and easily for proper cleaning becomes paramount. In such cases, carrying buffer stock for more difficult-to-clean parts can help minimize downtime by allowing for rapid reassembly in parallel to more time-consuming cleaning efforts.
Another aspect of sanitary design that has grown in importance is its contribution to allergen-free production. Producers that run packaging lines for both allergens and non-allergens pay close attention to hygienic machine designs. Consider a scenario where flow wrapping of both types of food bars are occurring on the same machine. Operators may clean all belts during a changeover, but a single positive equipment swab test for allergens can keep the line shut down far after changeover as additional cleaning is performed.
Hygienic practice isn’t just the machine design
This further emphasizes that the criteria for a hygienic packaging environment is not just the packing machine design itself, but the entire process:
- Deposit and filter systems
- Gas medium
- Packaging environment
- Operators handling product
Hygienic machine designs are important, and a fundamental aspect of food safety, but far from the only one. Operating a sanitary production environment requires producers to take many other safety measures. In the most general sense, the packaging machine should be installed in an environment appropriate for the handling of hygiene-sensitive products: uncluttered and free access around the machine, away from overhead utilities that can create dust or other foreign matter.
There should be enough clearance under the machine to enable adequate cleaning and inspection, and they should not be positioned over drains if doing so restricts drain inspection and cleaning. The mounting pads or feet should be suitably sealed to the floor, and connection methods for utilities (air, water, or electricity) can’t increase contamination risk.
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