The Five Second Rule Isn't True

Imagine it’s lunch.  You are holding a fat slice of melon.  It looks delicious.  You move in for the uh.....kill.  But something goes terribly wrong. The fruit slips from your fingers.  Time slows as the nutritious treat tumbles to the linoleum.  Rats!

You shrug, scooping up the slice.  Maybe you make a halfhearted attempt to brush it clean.  Maybe you even invoke that kitchen decree — the five-second rule — as you sink your teeth into its melon flesh.  "It was only four seconds.  I'm good!"

In case you’re not familiar with “the rule” it is 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.  The five-second rule is the fulcrum (pun intended) on which we balance our aversion to spoiled grub with our desire to scarf down the tasty stuff, belay the microbes.

Like most ideas concocted in cafeterias where pop tarts are avant garde 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.”  Uh-oh.

The Rutgers researchers dropped watermelon cubes, Haribo strawberry gummies, plain white bread and buttered bread onto various surfaces from a height of about five inches.

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.

“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, try not to drop that toast, friends.  And never drop your melon.

Bon appétit !!