Five second rule: Excuse to eat off the floor ‘debunked’ by US scientists

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Invoking the “five-second rule” has saved many a dropped morsel of food from the bin, but scientists have now debunked the unwritten law for eating off the ground.

The popular belief that food touching the floor for five seconds or less is safe to consume has been tested by Rutgers University, New Jersey, to determine once and for all if it has any merits.

Based on the assumption that bacteria needs time to transfer onto food, the rule has been the last bastion of the person hoping to salvage scraps from the floor.

But in a study published in the American Society for Microbiology journal, researchers have warned that the five second guide is not a foolproof rule to live, or should we say, dine by.

Day 2 of Summer and we already have a casualty ☀️🔥😵 #vsco #instadfw #fivesecondrule

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“We decided to look into this because the practice is so widespread,” said Rutgers food science professor Donald Schaffner, who also noted the rule had featured on television.

“The topic might appear ‘light’ but we wanted our results backed by solid science.”

Using watermelon, bread, buttered bread and gummy candy, bacteria contamination over a period of one, five, 30 and 300 seconds was tested.

A total of 2,560 experimental scenarios were carried out involving a noninfectious “cousin” bacteria to Salmonella, known as Enterobacter aerogenes.

During the study, the food was placed onto four different dry surfaces - stainless steel, ceramic tile, wood and carpet - all inoculated with the bacteria.

But the results make grim reading for anyone who has ever dusted off a piece of ‘floor candy’ - which according to a survey by Birmingham’s Aston University is 87 per cent of people.

The study concludes that bacteria transfer can take place “instantaneously,” although some food types are more germ friendly than others.

“The five second rule is a significant oversimplification of what actually happens when bacteria transfer from a surface to food. Bacteria can contaminate instantaneously,” said researcher Schaffner.

The testing revealed watermelon had the most contamination due to its high moisture content, while the candy received the least transfer of the Salmonella substitute.

“Transfer of bacteria from surfaces to food appears to be affected most by moisture,” Schaffner explained.

“Bacteria don’t have legs, they move with the moisture, and the wetter the food, the higher the risk of transfer.”

One saving grace for floor scavengers is that while food is likely to be invaded by potentially harmful bacteria the moment it hits a dirty surface, the less time there the better.

But if one really must eat from the ground, it appears that carpet, with its “low transfer” rate, is the better option compared with tiles or stainless steel.