We’ve all face this conundrum: that last delicious morsel of food, which you saved to enjoy last, helplessly falls to the floor. Rather than tossing it, you look around, and there’s no doubt you thought about picking it up and gobbling it down before anyone’s judging eyes locks in on you.
It’s the infamous ‘5-second-rule’, suggesting food that’s fallen to the floor, but immediately picked up and eaten, is okay as long as it’s consumed within those five seconds.
A new study, however, says that may be a myth.
The Centers for Disease Control and Prevention (CDC) says 1 in 6 people in the U.S. become sick due to foodborne illnesses, totaling to nearly 48 million people. Amongst that total, 3,000 succumb to those foodborne illnesses.
The authors of the 5-second-rule study noted that bacterial cross-contamination from surfaces – like the floor – to food, contributes to foodborne diseases. It’s the main reason they wanted to investigate the cliché further.
“We decided to look into this because the [5-second rule] practice is so widespread,” says Prof. Schaffner, from Rutgers University in New Brunswick, NJ.
“The topic might appear ‘light’ but we wanted our results backed by solid science.”
There have been past studies that suggest the 5-second-rule does hold true, though that research is limited to few peer-reviewed journals.
Prof. Schaffner says the rule is based on the idea that ‘bacteria need time to transfer.’ So, they had to find out: is picking up food in 5 seconds quick enough so the bacteria doesn’t move from surface to food?
Schaffner’s team used four surfaces in their study: stainless steel, ceramic tile, wood, and carpet. They also used four different foods: watermelon, bread, bread with butter, and gummy candy. For a diligent and thorough trial, they also used four different contact times – less than a second, 5 seconds, 30 seconds, and finally 300 seconds.
The bacteria they used in the experiment was Enterobacter aerogenes, which is a “cousin” of Salmonella, naturally produced in the human digestive system. It was smeared on the multiple surfaces, and dried before testing the food morsels.
In total, they tested 128 scenarios and combinations, replicated 20 times each, totaling 2,560 measurements. The results found watermelon to be the most easily contaminated, while the gummy candy stayed the cleanest. Interestingly, the discovered bacteria transfer is also affected by moisture.
“Bacteria don’t have legs,” says Prof. Schaffner. “They move with the moisture, and the wetter the food, the higher the risk of transfer. Also, longer food contact times usually result in the transfer of more bacteria from each surface to food.”
The research team concluded their study by saying that while longer contact times do result in more bacterial transfer, “other factors including the nature of the food and the surface are of equal or greater importance.”
So, they feel their thorough research finally, once and for all, disproves the 5-second-rule for good.
The team’s findings were published in the American Society for Microbiology’s journal, Applied and Environmental Microbiology.