Does the five-second rule hold any truth? If you quickly grab your dropped food before it has been in contact with the ground for too long, does it really remain germ-free? Of course not. Why would bacteria wait for five seconds before colonizing to your potato chip or apple slice? But it's not quite that simple, says a new study from Rutgers University.
"The popular notion of the 'five-second rule' states food dropped on the floor for less than five seconds is 'safe,' because bacteria need time to transfer," says the report. "The rule has been explored by a single study in the published literature and on at least two television shows."
The Rutgers researchers, then, set out to answer the question once and for all. To do so, researchers applied bacteria to four kinds of surfaces—stainless steel, tile, wood, and carpet—and dropped four kinds of food onto them: watermelon, bread, bread with butter, and gummy candy.
Once dropped, the foods were left in place for 1, 5, 30, and 300 seconds (5 minutes) before being snatched up.
The results show that—no surprise—longer contact times do indeed mean more bacteria on the food, but the kind of food dropped, and the type of surface it is dropped onto, both affect the results more than the contact time.
Wet watermelon picked up the most bacteria, and gummy candy the least. "Transfer of bacteria from surfaces to food appears to be affected most by moisture," study co-author Donald Schaffner told Rutgers News. "Bacteria don’t have legs, they move with the moisture, and the wetter the food, the higher the risk of transfer."
More surprising is that carpet, seemingly the grossest of all surfaces, was the cleanest in terms of bacterial transfer. This is most likely down to the "topography" of the materials. Viewed close up, you'll see that carpet doesn't touch the food as much as something smooth like steel or tile.
So, dropping a gummy candy onto carpet and then eating it will probably cause you less harm than the sugar in the candy, whereas soft, wet fruit dropped onto a wooden floor will be a bacterial feast, no matter how quickly you snatch it up. Not that either of those is necessarily safe or dangerous—that also depends on just how filthy the surface is to begin with. Still, the longer you leave the food in contact with a surface of any kind, the more contamination it picks up.
"Longer food contact times usually result in the transfer of more bacteria from each surface to food," said Schaffner, although that doesn't mean that you can rely on the five-second rule to keep your safe: "Bacteria can contaminate instantaneously," he said.
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