Hygienic construction

The main goal of the designer of a machine or a device is to ensure that the machine meets the functional requirements. The set objectives are achieved by meeting the functional requirements. The design must meet the necessary and legally required preconditions with regard to hygiene. No microbiological problems should arise, especially when the machine is in operation.

From a hygienic point of view, the designer must pay attention to the following matters:

• Cleanability and disinfection: the machine must be easy to clean as easy as possible.
• Preventing the entry of micro-organisms into products: the machine must be impermeable to micro-organisms.
• Preventing the growth of microorganisms: Especially blind spots, crevices and openings must be avoided.
• Coordination of hygienic requirements with functional requirements: hygiene requirements sometimes clash with functional requirements and compromises have to be made. These trade-offs almost always mean that it becomes more difficult to clean and disinfect the machine or device. Such trade-offs must be well documented and discussed with the user.
• Validating whether the hygiene requirements have actually been met: it is very important to check whether the hygiene requirements are actually being met. If this is not the case, the required hygiene level can sometimes be achieved with relatively simple adjustments. If any doubts remain, it is possible to make testing or inspecting the machine part of the regular maintenance procedures.

Design criteria

The following basic criteria are part of hygienic design:

• No imperfections in product surfaces,
• No non-welded direct metal-to-metal connections
• Good alignment of pipes and equipment. No imperfections.
• No O-rings coming into contact with the product. If this is nevertheless necessary, provide a flat, static seal.
• No direct product contact with threads.
• Avoid sharp corners (<90o). Radius of the corners between a minimum of 3 mm and a maximum of 6 mm.
• No sharp edges due to deburring
• Smooth surface finish and acceptable surface roughness,
• Product surfaces must have an acceptable surface roughness Ra. The maximum roughness for large contact surfaces is 0.8 μm,
• Avoid horizontal surfaces, both inside and outside the equipment, including the pipework,
• Liquids must be able to flow freely, always to one side,
• Prevent condensation on equipment and pipes. If this is not possible, condensation must be able to drain,
• Ensure good, smooth weld seams, also for surfaces that do not come into contact with the product. If this is not met, post-processing is necessary. This can be done by grinding or polishing the material,
• It must not be possible for water or dirt to remain on supports (for example in front of the pipes),
• If pipework or components need to be insulated, this can be done with a completely sealed stainless steel jacket. This mantle makes it impossible for air and / or moisture to penetrate. With double-walled pipes, insulation can take place by vacuuming the space between the walls.

Ultimately, all surfaces that come into contact with the product should be easy to clean by hand and easy to inspect visually. If this is not possible, it must be demonstrated how all contaminants can be removed.