Hygienic Design Principles: Dead Spots, Welds, and Surface Roughness

What Is Hygienic Design?

Hygienic design means designing a machine so that its food contact zones are easy to clean, easy to inspect, unlikely to harbor dirt, and won't carry contamination into food. It's different from "washing a few more times afterward"; it reduces the chance of cleaning failures through the structure itself.

Taiwan's regulations require the same thing in performance terms: Article 7 of the Standards for Food Factory Buildings and Equipment (食品工廠建築及設備設廠標準) requires equipment designs that prevent harm to food, are easy to clean, sanitize, and inspect, and keep lubricants, metal fragments, and wastewater out; GHP Annex 2 requires food contact surfaces to be kept smooth and free of dents or cracks.

Section 2.1 of Annex I of the EU Machinery Directive 2006/42/EC sets out hygiene requirements specifically for foodstuffs machinery. Key points include: contact materials must comply with the relevant rules; surfaces must be smooth, without ridges or crevices that could harbor organic matter; joints must be minimized; machinery must be easy to clean and disinfect, with parts removable where necessary; inside surfaces must have corner radii sufficient for thorough cleaning; cleaning fluids must drain completely; lubricants must not come into contact with food; and the instructions must specify recommended cleaning agents and methods. The EU has adopted a new Machinery Regulation, (EU) 2023/1230, which replaces 2006/42/EC from January 20, 2027.

Dead Spots

Dead spots are places that cleaning water and brushes can't reach, or where residue collects, for example:

• Dead legs and pipe sections without an outlet.
• Sharp inside corners and gaps between overlapping metal sheets.
• Screw heads and threads exposed in the contact zone.
• Recesses that can't drain.

Hygienic design replaces right angles with rounded corners, gives surfaces a drainage slope, moves fasteners outside the contact zone, or uses quick-release structures so every surface can be seen and washed.

Welds

Welds are where stainless steel equipment most often has problems: discontinuous, uneven welds, porosity, or slag all become hiding places for bacteria, and heat-tinted areas around welds have reduced corrosion resistance. Welds in contact zones are generally required to be continuous, ground and polished flush with the surrounding surface, and treated for heat tint.

Surface Roughness

The rougher a surface, the more easily microorganisms attach in tiny valleys and the harder they are to remove during cleaning. The industry commonly describes this with Ra (arithmetic mean roughness, in μm). According to equipment makers' summaries of EHEDG Guideline Doc 8, the figure often cited for food contact surfaces is Ra 0.8 μm or less; but Ra is only an average, and surfaces with the same Ra can still have different textures. Actual design and acceptance values should follow the original EHEDG or 3-A guidelines and the specifications agreed between buyer and seller.

Other Common Principles

• Drainage: Surfaces and piping drain naturally without standing water.
• Removability: Contact parts can be removed for washing without tools or with simple tools, and can't be reassembled incorrectly.
• Isolating lubrication and drives: Bearings, gears, and chains are placed outside the contact zone, with shaft seals designed to prevent lubricant from seeping in.
• Material compatibility: Avoid contact between dissimilar metals that causes corrosion; plastics and seals must withstand cleaning agents and temperatures.
• Inspectability: Once disassembled, contact surfaces are visible to the naked eye so you can confirm they're clean.

What Are EHEDG and 3-A?

• EHEDG (European Hygienic Engineering & Design Group): Made up of equipment makers, food companies, and research institutes, it publishes a series of hygienic design guidelines and also offers hygienic design certification for equipment. Website: ehedg.org.
• 3-A Sanitary Standards: A US sanitary standards organization that originated in the dairy industry. It develops sanitary standards and accepted practices for equipment, and compliant equipment can carry the 3-A symbol. Website: 3-a.org.

Both are voluntary industry standards, not Taiwanese regulations; but when exporting to Europe or the US or supplying international brands, customers often use them as the basis for equipment specifications.

Look at Your Own Machines From This Angle

When buying or accepting an encrusting machine or divider, you can go through a simple checklist item by item: can the contact parts be removed, can every surface be seen once removed, are there right-angle crevices, are the welds smooth, where are the lubrication points, and does cleaning water pool on the machine? For how Dong-Yih models are disassembled and washed, please call 06-257-4644. For scheduling equipment cleaning, see Allergen Management and Machine Changeover Cleaning.

FAQ

Q: What is hygienic design?
A: Designing a machine from the start so that its food contact zones are easy to clean, easy to inspect, and don't harbor dirt, while keeping contaminants such as lubricants and debris out of food.

Q: What surface roughness should contact surfaces have?
A: The industry often cites Ra 0.8 μm or less from EHEDG guidelines; Taiwan's regulations don't set a number and only require surfaces to be smooth and free of dents or cracks. Actual values follow the original guidelines and contract specifications.

Q: What are EHEDG and 3-A?
A: EHEDG is a European hygienic engineering and design organization, and 3-A is a sanitary standards organization that originated in the US dairy industry. Both publish hygienic design guidelines for equipment and offer certification or a symbol; they are voluntary standards.

Q: Where are the EU's hygiene requirements for food machinery?
A: Section 2.1 of Annex I of the Machinery Directive 2006/42/EC; the new Machinery Regulation (EU) 2023/1230 replaces that directive from January 20, 2027.