Have you heard that if you drop food on the floor, it’s still safe to eat for five seconds?
It’s an intriguing idea, but where did it come from?
We can’t be sure who thought of the five-second rule first, but some attribute it to Genghis Khan. No, really! “There were some historical quotes from Genghis Khan about eating food off the floor in reference to a ‘if it was good enough for him, then it was safe for everybody’ kind of a response,” said Paul Dawson, professor at Clemson University’s food, nutrition, and packaging sciences department.
But 13th-century Mongols didn’t know about microorganisms and the illnesses they could cause, so eating foods off the floor may have seemed fine to them, according to the book “Did You Just Eat That?” written by Dawson and Brian Sheldon.
Another possible source is a story about Julia Child, who reportedly dropped a piece of meat and picked it up with the comment that if you’re alone in the kitchen, no one will see you. But according to Dawson, the story isn’t true. “We couldn’t track down exactly when it started,” he said. “I think it’s just one of those society myths that kind of got started and people kept propagating it.”
So we don’t know where the five-second rule came from, but the real question is its veracity. Is it really true?
Both Dawson and Schaffner have actually studied what happens when different foods come in contact with various surfaces. In a 2006 study published in the Journal of Applied Microbiology, Dawson and other researchers investigated how the length of time food was in contact with a contaminated surface affected bacteria transfer. They tested three floor types ― tile, wood and carpet ― contaminated with salmonella, and two kinds of food: bologna and bread.
They found the floor’s contamination level and the type of surface mattered most. Carpet contained more bacteria longer, but didn’t transfer as much to the foods; carpet’s porous surface enabled bacteria to seep in and not stand on the surface as much. Also, while how long food is on the floor is important, the food type and what’s actually on that floor is just as critical. For example, bacteria transfer was high for foods with a high moisture content, like watermelon cubes. “We think this is because the moisture facilitates movement of the bacteria from the surface to the food,” Schaffner explained. “Bacteria don’t have legs, so they really do require something like moisture to allow them to move.”
The key is whether the surface is actually contaminated. “I would trust my freshly mopped kitchen floor more than I would trust another surface like a New York City subway platform,” Schaffner said.
So can we trust the five-second rule? In a word, no. “It’s pretty much a myth,” Dawson said. “It really depends on what’s on the ground and where the food lands.” Food will pick up bacteria immediately, “so you’re just gambling if you eat it and you’re not sure what’s on that surface.” Schaffner puts it this way: “There is no ‘safe’ amount of time when no bacterial will transfer.”
For more information, see “Does The 5-Second Rule Actually Mean It’s Safe To Eat Food Off The Floor?” by Erica Sweeney (https://www.huffpost.com/entry/5-second-rule-food_l_619bb219e4b025be1adf16c3?).