A straightforwardly titled study — “Is the Five-Second Rule Real?” — led by food microbiologist Donald W. Schaffner at Rutgers University has sadly concluded that no, it’s not. Alas, if you pick up food from the floor, germs are probably coming with it.
The finding appeared online this month in the American Society for Microbiology’s journal, Applied and Environmental Microbiology.
An earlier study from Aston University’s School of Life and Health Sciences in England had suggested that food picked up just a few seconds after being dropped was “less likely to contain bacteria than if left for longer periods of time,” but Schaffer noted that this study did not appear in a peer-reviewed journal.
Schaffer’s study tested four foods (sliced watermelon, bread with and without butter and strawberry-flavored gummy candy) on four surfaces (stainless steel, ceramic tile, wood and carpet). The surfaces were treated with bacteria similar to salmonella; the foods dropped from a height of five inches. Four contact times — less than one second, five seconds, 30 seconds and 300 seconds — yielded a total of 128 possible combinations that were replicated 20 times each for 2,560 measurements.
So yes, it’s probably safe to call this the definitive study on the five-second rule.
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The takeaway: While the concept of the five-second rule is somewhat valid — the longer food remained in contact with the surface, the more bacteria was transferred — there was no situation in which food escaped contamination completely.
“Bacteria can contaminate instantaneously,” Schaffner’s press release concluded.
That said, if you’re a butterfingered eater (literally, not figuratively), carpet had lower transmission rate than tile and stainless steel, while transfer rates from wood varied. The food’s composition and the surface it fell upon were both bigger factors than exposure time, Schaffner found — porous and wet watermelon gathered more bacteria than the hard surface of the gummy candy.
Regarding his own eating practices, Schaffner told the New York Times: “I will tell you on the record that I’ve eaten food off the floor,” before adding, “If I were to drop a piece of watermelon on my relatively clean kitchen floor, I’m telling you, man, it’s going in the compost.”