Study: Five-second rule is too generous for fallen food

Researchers at Rutgers University in New Jersey say in a new study that bacteria can contaminate food that falls on the floor instantaneously. Photo / 123RF

It might be time to reconsider the five-second rule when thinking about eating food that has fallen on the floor.

Researchers at Rutgers University in New Jersey say in a new study that bacteria can contaminate food that falls on the floor instantaneously.

The findings were published this month in the American Society for Microbiology's journal.

Researcher Donald Schaffner said the five-second rule is a "significant oversimplification of what actually happens when bacteria transfer from a surface to food."

Schaffner's research isn't the first to conclude that the favorite excuse for why that yummy snack that fell on the ground is still OK to eat is wrong.

The Rutgers researchers dropped watermelon cubes, Haribo strawberry gummies, plain white bread and buttered bread (purchased from a New Jersey ShopRite) 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.

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 tests. 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.

"Bacteria don't have legs, they move with the moisture," as Schaffner pointed out. Wet food, therefore, had the most risk of transfer.

- AP, Washington Post