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Superheated or 'dry' steam shows sanitation potential

March 22, 2023
Dry facilities, such as some packing operations, may not be able to use water-based sanitizers. In fact, some facilities may even lack floor drains.
To expand potential microbial sanitation options for those operations, Abby Snyder, Ph.D., with Cornell University, is leading research to evaluate how well superheated steam (SHS) works and determine how current tools need to be improved to better support the produce industry.

Key Take-Aways

• Superheated steam or dry steam can kill pathogens on environmental surfaces without leaving moisture or condensation.
• Researchers looked at thermal distribution across stainless steel coupons using different temperatures and nozzle distances.
• Project also will address several considerations including cost, range of applications, wear and tear on equipment and worker safety.
• Online survey will gauge how much packing facilities are willing to pay for SHS technology.
Also known as dry steam, SHS can kill pathogens on environmental surfaces, according to previous research. But little is known about its performance on a pilot scale.
As part of her research, titled “Practical application of superheated steam to harvesting, processing, and produce packing tools and equipment,” Snyder also plans to address other considerations, including cost, range of applications, wear and tear on equipment, changes to ambient relative humidity and worker safety.
“It’s a really tough problem to solve,” Snyder said. “We wanted to bring some practical assessments to our academic research to better understand whether these tools would be useful to the industry.”
Joining her as co-principal investigator is V.M. Balasubramaniam, Ph.D., with Ohio State University, who brings expertise in food and agricultural engineering.
“He’s an important collaborator because the project is at the intersection of produce safety and process engineering,” said Snyder, whose background is microbial food safety. “This is an interdisciplinary approach to developing novel sanitation technology.”
Superheated steam differs from the visible, wet steam vapor emitted by a tea kettle in that it is invisible and acts like a hot gas at super-high temperatures. Applied to surfaces, superheated steam has been shown to kill pathogens without leaving moisture or condensation. 
The researchers used portable pilot-scale roll-along and backpack units fabricated by a collaborating manufacturer. As part of the project, they reviewed Occupational Safety and Health Administration guidelines and developed worker safety and operator compliance training.
Initial trials looked at thermal distribution across stainless steel coupons — or discs — at ambient temperatures using three different coupon thicknesses and three different nozzle distances.
Temperatures at the contact point ranged from 170 to 320 degrees Celsius (338 to 608 degrees Fahrenheit), depending on nozzle distance. Compare that to commercial pizza ovens, which typically range from 400 F to 800 F. 
High temperatures support short exposure times, and the team also plans to characterize how rapidly temperature dissipates across the surface. The researchers plan to conduct similar tests with concrete coupons as well as ones made of materials used in picking bags.
Although superheated steam doesn’t use large amounts of water, it is unknown whether prolonged use of the technology could change ambient relative humidity in enclosed spaces, depending on size and ventilation. As part of the project, Snyder said they will look at whether those relative humidity changes could potentially lead to condensation with extended superheated steam use.
One of the project’s objectives is to better understand how much the industry would be willing to pay for SHS technology. To that end, Snyder is conducting a brief online survey that proposes different scenarios. Respondents remain anonymous. To participate in the survey, visit
Because superheated steam doesn’t use large amounts of water, Snyder said the technology could offer the produce industry potential water savings. But it also could provide the industry with more sanitation options.
“I think these practical findings will lead to the development of better sanitation equipment in the produce industry. We’re moving it forward from theoretical research to something practical.”
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