Food on Floor 'Five Second Rule' Debunked

Eating food off the floor is not safe as bacteria may transfer in less than a second, says a new study that disproves the widely accepted notion that it is alright to scoop up food within a “safe” five-second window. Researchers found 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 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. While the pop culture “rule” has been featured by at least two TV programmes, research in peer-reviewed journals is limited. The researchers tested four surfaces – stainless steel, ceramic tile, wood and carpet – and four different foods (watermelon, bread, bread and butter, and gummy candy).

They also looked at four different contact times – less than one second, five, 30 and 300 seconds. They used two media – tryptic soy broth or peptone buffer – to grow Enterobacter aerogenes, a non pathogenic “cousin” of Salmonella naturally occurring in the human digestive system. Transfer scenarios were evaluated for each surface type, food type, contact time and bacterial prep; surfaces were inoculated with bacteria and allowed to completely dry before food samples were dropped and left to remain for specified periods. All totaled 128 scenarios were replicated 20 times each, yielding 2,560 measurements. Post transfer surface and food samples were analyzed for contamination. Not surprisingly, watermelon had the most contamination, gummy candy the least.