First of all, you should know that neither of us is overly paranoid about germs. If you could see the tea mugs we drink out of, you would be amazed that we remain reasonably healthy. In general, it seems harmless enough to eat something that you dropped on the floor for just a few seconds. (Okay, so maybe you wouldn’t follow the five-second rule in a public toilet, but other than that it doesn’t sound like such a bad idea.)
That is, until you start reading the work of scientists who specialize in food science and microbiology, the studies of how bugs get into our food and stay there. We are not sure how these scientists manage to eat anything without being paranoid, and, unfortunately for us, they decided to put the five-second rule to the test.
Food scientists conducted three experiments to find out what happens when the five-second rule comes up against Salmonella typhimurium, a fairly common but nasty bacterium that can cause wretched diarrhoea and vomiting. They tested how well Salmonella survived on wood, tile and carpet, and they tested how well it transferred from these surfaces to either bologna sausage or bread. They found that bacteria were still alive after four weeks on dry wood, tile or carpet, and that enough of the bacteria survived to be able to transfer to food. Next, the scientists tested how much time it took for the bacteria to transfer from these different floor surfaces to the food. The worst offender of the five-second rule was bologna on tile. Over 99 per cent of the bacterial cells transferred from the tile to the bologna after just five seconds of the bologna hitting the floor! Transfer from wood was a bit slower (5 to 68 per cent of the bacteria were transferred) and transfer from carpet was actually not very successful. After hitting the carpet, less than 0.5 per cent of the bacteria transferred to the bologna. When they did transfer, bacteria moved to the food almost immediately upon contact. By five seconds, it was too late. Other bacteria, like Campylobacter and Salmonella enteritis, can also survive well on formica, tile, stainless steel, wood and cotton cloths, so if you listen to the microbiologists, you can never be too careful about cleaning things up in the kitchen, and you also can’t trust the five-second rule. Bacteria that can make you ill can survive on the floor or other surfaces for a long time, and they can contaminate other foods that touch them for only a few seconds.
Bacteria aren’t the only thing that could make you ill when your food hits the floor. A study of pesticides on household surfaces shows that these toxic chemicals can also transfer to foods like apples, salami and cheese. The pesticides seem to take a little longer than bacteria, though. The average pesticide was only 1 per cent efficient in transferring over to the food at the one-minute mark, but up to 83 per cent transferred if it was left on the floor for sixty minutes. Applying more force to the food (like throwing it against the floor) also resulted in more pesticide getting on the food, up to 70 per cent at ten minutes on hardwood flooring when bologna was squished with a force equivalent to 1.5 kg.