From 'Good enough' to 99.99%

Tunnel steam ovens are brilliant for cooking – and a pain to clean. You have a long, hot, enclosed chamber with a wire mesh belt running through it.

Fats, proteins and marinades drip onto the belt and frame, then carbonise and stick to metal surfaces like varnish. The belt has wires, edges and joints where residues love to hide. Add steam and condensation, and you end up with sticky, burnt-on deposits that are hard to reach and even harder to remove properly with manual cleaning.

That was exactly the situation for a manufacturer of roasted and marinated products running a tunnel steam oven with a stainless-steel belt. The existing manual cleaning method seemed to work, but the quality team wanted better cleaning results.

ATP swab tests on three areas of the tunnel belt (left side, entry and right side) showed:

• Before cleaning: ATP values in the 95,000–160,000 RLU range*
• After the manual method: still 1,600–3,800 RLU left on the surface
• Calculated cleanliness: 97–98%

On paper, this met the internal criterion of “more than 90% cleanliness”, so it technically passed – but it didn’t leave much safety margin, especially on a belt that carries high-risk, sticky products through a closed system.

To ensure the final products were of the highest quality, a higher level of cleanliness was needed.

*RLU (Relative Light Units) is the number shown by the ATP test device. The device turns any food residue or microbes on the surface into a tiny flash of light and measures its brightness. The more light (higher RLU), the more organic contamination is present; the lower the RLU, the cleaner the surface.

The plant therefore wanted to test an automated cleaning system for the tunnel belt and then repeat the tests. The new process was designed to:

• Reach the full belt width, including sides
• Flush out residues rather than just brushing them around
• Rinse thoroughly so no detergent remains on the surface

With the automated system in place:

• Post-cleaning ATP: dropped to between 5 and 12 RLU
• Cleanliness: 99.99% in all three test areas
• Pass rate: 100% of tests above the ≥90% cleanliness criterion
• Chemical check: pH-paper tests confirmed no detectable chemical residue on the belt or in the rinse water

In everyday language: the manual method left the belt reasonably clean; the automated system left it virtually spotless and free of detergent residues.