Researchers Debunk The ‘Five-Second Rule’: Eating Food Off The Floor Isn’t Always Safe


Surprisingly, it turns out that no matter how fast you pick up food that has fallen to the floor, bacteria may transfer to it.

The Rutgers Researchers have strongly disproved the “safe” five-second window which is the widely accepted notion that it is ok to pick up food that has fallen on the ground within five seconds and eat it. It was found by Donald Schaffner, professor and extension specialist in food science, that moisture, type of surface and contact time all contribute to the rate of contamination and that in some instances, the transfer begins in less than a second. Their findings appear online in the American Society for Microbiology’s journal, Applied and Environmental Microbiology.

According to Schaffner, “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.” He also added that while the pop culture “rule” has been featured by at least two TV programs, research in peer-reviewed journals is limited.

Schaffner, who conducted research with Robyn Miranda, a graduate student in his laboratory at the School of Environmental and Biological Sciences, Rutgers University-New Brunswick said, “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.”

During the research, the researchers tested four surfaces which were – stainless steel, ceramic tile, wood and carpet – with four different foods – watermelon, bread, bread and butter and gummy candy. They also used four different contact times; less than one second, five, thirty and three hundred seconds. They used two media, tryptic soy broth or peptone buffer, to grow Enterobacter aerogenes, a nonpathogenic “cousin” of Salmonella naturally occurring in the human digestive system.

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For each surface type, food type, contact time and bacterial prep, the transfers were evaluated. Before the samples were dropped and left to remain for specified periods, surfaces were inoculated with bacteria and allowed to completely dry. Post-transfer surface and food samples were analyzed for contamination. In total, 128 scenarios were replicated 20 times each, yielding 2,560 measurements.

According to Schaffner, “Transfer of bacteria from surfaces to food appears to be affected most by moisture.” Not surprisingly, watermelon had the most contamination and gummy candy the least. “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.” He added.

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

So while the finding of the research shows 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.

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