The ‘five-second rule’ food rule goes under review

Oh no! Eating food off the floor is not safe‚ even when you apply “the five-second rule”.

Researchers at Rutgers University in the United States have disproved the “widely accepted notion” that it’s acceptable to eat food that has fallen on the ground‚ according to a recently published study.

The study - Longer Contact Times Increase Cross-Contamination of Enterobacter Aerogenes from Surfaces to Food - which was written by Robyn Miranda and Donald Schaffner‚ found that moisture‚ type of surface and contact time all contribute to “cross-contamination”.

According to Miranda and Schaffner’s study - which appears online in the American Society for Microbiology's journal‚ Applied and Environmental Microbiology - in some instances‚ bacterial transfer begins in less than one second.

“The popular notion of the 'five-second rule' is that food dropped on the floor‚ but picked up quickly‚ is safe to eat because bacteria need time to transfer‚" Schaffner said in a statement published by Rutgers.

“We decided to look into this because the practice is so widespread.

“The topic might appear ‘light’ but we wanted our results backed by solid science‚” Schaffner added.

According to Rutgers University‚ the researchers tested four surfaces – stainless steel‚ ceramic tile‚ wood and carpet – and four different foods (watermelon‚ bread‚ bread and butter‚ and gummy candy).

They also looked at four different contact times – less than one second‚ five‚ 30 and 300 seconds.

“Transfer scenarios were evaluated for each surface type‚ food type‚ contact time and bacterial prep; surfaces were inoculated with bacteria and allowed to completely dry before food samples were dropped and left to remain for specified periods.

“All totalled 128 scenarios were replicated 20 times each‚ yielding 2560 measurements. Post-transfer surface and food samples were analysed for contamination‚” the university statement read.

It was noted that watermelon had the most contamination‚ gummy candy the least.

“Transfer of bacteria from surfaces to food appears to be affected most by moisture‚” Schaffner said.

“Bacteria don’t have legs‚ they move with the moisture‚ and the wetter the food‚ the higher the risk of transfer. Also‚ longer food contact times usually result in the transfer of more bacteria from each surface to food.”

Carpet surfaces were found to have “very low transfer rates” compared with those of tile and stainless steel‚ “whereas transfer from wood is more variable”.

“The topography of the surface and food seem to play an important role in bacterial transfer‚” Schaffner said.

The university statement went on to add that‚ while the researchers demonstrate that the five-second rule is “real” in the sense that longer contact time results in more bacterial transfer‚ it also shows other factors‚ including the nature of the food and the surface it falls on‚ are of equal or greater importance.

“The five-second rule is a significant oversimplification of what actually happens when bacteria transfer from a surface to food.

“Bacteria can contaminate instantaneously‚” Schaffner said.

- TMG Digital