Superheated steam dishwasher could kill bacteria in just 25 seconds

Computer simulations of a simplified dishwasher that uses hot, dry steam and no detergent found that it could kill all heat-resistant bacteria on a plate in under half a minute – but it might not actually clean your dishes

By Karmela Padavic-Callaghan

A superheated steam dishwasher could kill heat-resistant bacteria on a plate in less than 30 seconds, computer simulations suggest.

Natalie Germann at TU Dortmund University in Germany and Laila Abu-Farah at the Technical University of Munich in Germany modelled a simplified dishwasher that used very hot steam to clean, rather than hot water and soap.

When steam reaches a high enough temperature, it becomes “superheated”, meaning all the water droplets evaporate so it is purely gaseous and dry. In this form, it can transfer more heat when it hits a surface than conventional steam.

The researchers simulated a simple device that could use superheated steam to clean dishes on a computer. It consisted of a nozzle shooting out superheated steam into a box containing a single plate with heat-resistant bacteria on it. The bacteria was modelled on Geobacillus stearothermophilus, which can cause food to spoil and can survive in temperatures above those that normal dishwashers reach.

After 2 seconds of the simulation, about 50 per cent of the bacteria were dead. After 25 seconds their concentration on the plate fell to zero.

Germann says that in a machine with more nozzles and more dishes this would probably take longer than half a minute, but she expects it would still be shorter than in conventional dishwasher where the average cycle lasts 1.5 hours.

Abigail Snyder at Cornell University in New York says that superheated steam is already used as a sanitiser in commercial food processing plants because it is an effective alternative to using detergents that can sometimes be harmful. However, she says that superheated steam can’t be the only washing method because it wouldn’t remove bits of food that are stuck to dishes.

Superheated steam dishwashers could be an option for sterilising medical instruments, says Rainer Stamminger at the University of Bonn in Germany. However, the very high temperatures may prove challenging for use in homes and cause damage to some dishes, he says.

Germann and her colleagues are planning to next simulate more complex versions of their dishwasher by adding more nozzles and more dishes.

Journal reference: Physics of Fluids, DOI: 10.1063/5.0090418