Is eating food that has fallen to the floor ever truly safe? Many cling to the “5-second rule,” which asserts that, if you pick up dropped food within five seconds of it hitting the ground, it’s still safe to eat. Now, researchers at Rutgers have disproved the widely accepted notion. They found that moisture, the type of surface, and contact time all contribute to cross-contamination. In some instances, the transfer of bacteria begins in less than one second. The researchers tested four surfaces – stainless steel, ceramic tile, wood and carpet – and four different foods — watermelon, bread, gummy candy, and bread and butter. They also looked at four different contact times – less than one second, five seconds, 30 seconds and 300 seconds. Surfaces were inoculated with bacteria and allowed to completely dry before food samples were dropped and left to remain for the specified periods. Not surprisingly, watermelon had the most contamination, with the gummy candy having the least. Transfer of bacteria from surfaces to food appears to be affected most by moisture. 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. Perhaps unexpectedly, carpet has very low transfer rates compared with those of tile and stainless steel, whereas transfer from wood is more variable. So while the researchers demonstrated that the 5-second rule is “real” in the sense that longer contact time results in more bacterial transfer, it also shows other factors, including the nature of the food and the surface it falls on, are of equal or greater importance. The bottom line: bacteria can contaminate instantaneously.
