Researchers believe that no matter how fast you pick food up from the floor, there’s a high chance that cross-contamination has already taken place.
The cross-contamination five-second rule is the belief that food dropped on the ground is still good to eat if picked up within five seconds.
Some researchers are now persuaded that bacteria sticks to things in less than a second. However, this largely depends on the type of food and the surface on which it was dropped.
Donald Schaffner who is a professor and extension specialist in food science deduced that moisture, type of surface and contact time add to cross-contamination.
“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,” Schaffner said.
“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,”
Four foods and four different surfaces were experimented on in the study. The foods were watermelon, bread, bread and butter, and gummy candy. The surfaces tested on were; stainless steel, ceramic tile, wood and carpet. They also compared four different contact times– less than 1 second, 5, 30 and 300 seconds for each food and surface.
They used two media in growing bacteria which were later applied on these surfaces and left to dry. The experiment began and each scenario was replicated 20 times for accuracy.
Water is bacteria’s ‘legs’
Following these, the food samples and the surfaces were analyzed for contamination. The result showed that watermelon had the most cross-contamination while gummy candy had the least.
Also, different surfaces had different rates of cross-contamination. Carpet had the lowest compared to tile and steel while wood was variable.
“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. Also, longer food contact times usually result in the transfer of more bacteria from each surface to food.”
The study shows that although the five-second rule makes sense, it oversimplifies the fact that bacteria can transfer faster onto food.
The study which was conducted by Robert Schaffner in conjunction with Robyn Miranda, a graduate student in his laboratory at the School of Environmental and Biological Sciences, Rutgers University-New Brunswick.
Their findings can be found in the American Society for Microbiology’s journal, Applied and Environmental Microbiology.