Scientists reveal gross truth behind the ‘five second rule’
Imagine it’s lunch. You are holding a fat slice of watermelon. It looks delicious. You move in for a bite. But something goes terribly wrong. The fruit slips from your juice-slicked fingers. Time slows as the nutritious treat tumbles to the linoleum.
Eh. You shrug, scooping up the slice. Maybe you make a halfhearted attempt to brush it clean. Maybe you even invoke that childhood decree – the five-second rule – as you sink your teeth into its melon flesh.
If you are unfamiliar with the rule, if you were never a klutsy fourth-grader with a sweet tooth and a fistful of M&Ms, it is simply this: If you drop food to the ground, you have a five-second window to pick it up and the snack will remain clean enough to eat.
Like most ideas concocted in cafeterias where the French toast sticks are haute cuisine, this rule does not hold up under intelligent, or basically any, scrutiny – including a new study published in the journal Applied and Environmental Microbiology.
“The five-second rule is a significant oversimplification of what actually happens when bacteria transfer from a surface to food,” Donald Schaffner, a Rutgers University biologist and an author of the research, said in a statement. “Bacteria can contaminate instantaneously.”
We know it does not make sense, but the five-second rule sticks anyway. As Monica Hesse wrote at The Washington Post in 2007: “The beauty of the five-second rule is that it is utterly pliable and that it is not about food so much as it is about yearning and disgust and gastronomic history and evolutionary wiring and the implicit social contract we make when we break (and drop) bread with other human beings.”
The five-second rule is the fulcrum on which we balance our aversion to spoiled grub with our desire to scarf down the tasty stuff, microbes be damned. (This is the point where we should mention there are 31 known pathogens responsible for an estimated 9 million cases of food-borne illness a year, according to the Centers for the Disease Control and Prevention.)
Though the origins of the five-second rule are murky, it is possible the tension it represents has always existed. Clemson University food scientist Paul Dawson points to Julia Child flubbing a potato pancake flip in an early episode of The French Chef as a sort of precursor. Her pancake doesn’t land on the floor, just on the stovetop, so she cooks it anyway. But Child seals her destiny as the patron saint of the wayward lamb with a quote: “Remember, you are alone in the kitchen and nobody can see you.”
Somewhere along the line, the five-second rule came to be. By the year 2000, at least, the folkloric rule had matured enough to star in a Volkswagen Passat commercial. A cursory search into the depths of the internet yielded a few turn-of-the-21st-century mentions that progressively picked up steam.
Food science experts have been trying to understand – and debunk – the notion ever since. The show MythBusters busted it in 2005. Clemson’s Paul Dawson published the first peer-reviewed study taking a crack at the rule in 2007. The new study aims to be a coup de grace: The paper is the best, most comprehensive evidence to date that, as a rule, the five-second method does not hold up.
The Rutgers researchers dropped watermelon cubes, Haribo strawberry gummies, plain white bread and buttered bread onto various surfaces from a height of about 10 centimetres.
Those surfaces – carpet, ceramic tile, stainless steel and wood – were slathered with Enterobacter aerogenes, a bacteria similar in food-clinging ability to salmonella but far less a dangerous bug. The scientists left the food on the surfaces for intervals varying from less than a second to five, 30 and 300 seconds.
All told, the researchers performed each different type of drop (for instance, gummy on wood, five seconds; watermelon on stainless steel, less than a second) 20 times apiece, totaling 2,560 measurements. The scientists then assessed how much E. aerogenes transferred between surface and food.
Although time was a factor – broadly speaking, the longer a food touched a surface the more bacteria it had – what was far more relevant was the composition of food or surface.
“Bacteria don’t have legs, they move with the moisture,” as Schaffner pointed out. Wet food, therefore, had the most risk of transfer. Watermelon soaked up the most bacteria, the Haribo candies the least.
To the surprise of the researchers, carpet transferred fewer bacteria than steel or tile. Wood was hard to pin down, showing a large variation.
The scientists concluded their paper, echoing Schaffner’s statement: The five-second rule is a “significant oversimplification” for the chance of bacteria transfer in real life. In other words, don’t drop that watermelon.
The Washington Post
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