Think the '5-second rule' means it's okay to eat food you dropped on the floor? Think again!

[Originally published on May 27, 2018]

When a morsel of a favourite food drops to the floor, people often invoke "the five-second rule," which says it's safe to eat if it's picked up quickly. 

Donald Schaffner, a food scientist at Rutger's University in New Brunswick, New Jersey, prefers hard science to common wisdom. He and a graduate student decided to put "the five-second rule" to the test. 

In their experiment, published in the journal of the American Society for Microbiology, they dropped four different foods onto four different surfaces and left them there for different lengths of time, then measured the extent of food contamination.

What we discovered was that the type of food [dropped] makes a huge difference.- Donald Schaffner

"What we discovered was that no matter which food or which surface...we saw some bacteria transfer," says Schaffner. "So what we conclude from that is there is no safe amount of time [to leave food on the floor.] You cannot be completely risk-free." 

The experiment involved dropping bread, bread with butter, watermelon and gummy candy on wood, stainless steel, ceramic tile and carpeting. 

"What we discovered was that the type of food makes a huge difference," says Schaffner. "If you really want to get a lot of germs off of a surface, the best food to use is watermelon. Because of the water in watermelon, it absorbed millions of bacteria almost instantaneously, no matter how long we left the food to sit on that surface."

Schaffner says the floor surface also makes a difference. He explains why the least amount of contamination occurred when food was dropped on a carpet.

This interview with Michael Enright was another instalment of our occasional series, "Think Again." Click 'listen' at the top of the page to hear Michael's conversation with Donald Schaffner.