You might have heard of the five-second rule – the widely accepted notion that food dropped on the floor is safe, as long as you pick it up within five seconds.
Researchers at Rutgers University, New Brunswick, have shown it isn’t so, that bacteria can contaminate a sweet that has fallen on the floor no matter how fast you pick it up.
“The popular notion of the ‘five-second rule’ is that food dropped on the floor, but picked up quickly, is safe to eat because bacteria need time to transfer,” said Donald Schaffner, professor and extension specialist in food science.
“We decided to look into this because the practice is so widespread. The topic might appear ‘light’ but we wanted our results backed by solid science.”
The results showed that moisture, type of surface and contact time all contribute to cross-contamination. In some instances, the transfer begins in less than one second.
The researchers tested four surfaces – stainless steel, ceramic tile, wood and carpet – and four different foods (watermelon, bread, bread and butter, and gummy candy).
Unexpectedly, researchers found carpet has very low bacteria transfer rates compared with those of tile and stainless steel.
Also surprisingly, watermelon had the most contamination and gummy candy the least.
“Transfer of bacteria from surfaces to food appears to be affected most by moisture,” Schaffner said. “Bacteria don’t have legs, they move with the moisture, and the wetter the food, the higher the risk of transfer.
“The five-second rule is a significant oversimplification of what actually happens when bacteria transfer from a surface to food,” he added. “Bacteria can contaminate instantaneously.”