You’re enjoying that ice cream so much, it feels like an explosion of flavour melting in your mouth. Alas, you don’t realise that your scoop of ice cream is slowly making its way to the floor. Can you salvage some of your ice cream and lick it off the floor? It’s fine, there’s the five-second rule, right? Or maybe not…

The five-second rule states that food is safe to eat off the floor if it is picked up within five seconds. Researchers have tested various food on different surfaces in order to check bacterial transfer. The surfaces tested were, stainless steel, ceramic tile, wood and carpet where the food that was dropped included watermelon, dry bread, buttered bread and gummy candies.

These foods were then dropped on a bacteria-covered surface and left for an amount of time: one second, five seconds, 30 seconds and 300 seconds. The bacteria used is a safe non-pathogenic relative of Salmonella, Enterobacter aerogenes.

Researchers found that bacteria transfer depends on the amount of moisture in the food, as well as the surface that it is dropped on. Bacteria transfer does not follow the five-second rule. The longer it is left on the ground, the more bacteria is transferred to the food. Their mode of transfer is faster if the food is wet and sticky like a watermelon.

So while contamination is higher the longer it’s left on the ground, bacteria certainly doesn’t wait five seconds to infest the food, especially if it is moist. This research was published in Applied and Environmental Microbiology.

So the next time you’re enjoying your last morsel of food and this happens to fall on the ground, pick it up, throw it out and mourn your food while thinking about what you can eat next.

For more information: www.sciencealert.com.