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5 second rule holds truth?

By Joe Whitworth+

14-Mar-2014
Last updated on 14-Mar-2014 at 14:58 GMT

5 second rule: Fact or fiction?
5 second rule: Fact or fiction?

The ‘five second rule’ about picking up food after it has been dropped on the floor may have some scientific basis, according to research.

Aston University researchers looked at two pathogens from three indoor floor types and transfer to toast, pasta, biscuit and a sticky sweet when contact was made from three to 30 seconds.

The research team analysed the survival of bacteria on surfaces and transfer onto other foods.

E.coli and Staphylococcus aureus were most likely to transfer from laminate or tiled surfaces to moist foods in contact for more than five seconds.

Carpeted surfaces were the least likely surface for the bacteria to transfer from.

Research last year from Dr Ronald Cutler, a microbiologist from Queen Mary, University of London, concluded the five second rule was a ‘myth’ and food dropped on any type of floor surface should be thrown away.

Surface structure

Professor Anthony Hilton, head of biological and biomedical science at Aston University, said the structure of the surface did have an impact.

“Food seems to be held up on the fibres, as it hits the carpet and the fibres hold it up so it doesn’t get full contact like it does on the tile and the laminate,” he told FoodQualityNews.com.

“I am not suggesting for a moment that the food industry carpets all the floors but there could be things to learn with the fibres role in contact area and how organisms transfer.”

He said E.coli and Staphylococcus aureus were chosen as they are often used as lab models representative of a variety of microorganisms as a common way to see if a model will work.

On laminate and tile E. colidrops one log every six days and S.aureusdrops one log every 12 days.

On carpet E. coli drops one log every 0.5 day and S.aureus drops one log every 3.5 days.

“Current thinking is that with the five second rule it is five seconds before the organisms transfer – immediately there are none and after five seconds they all jump on,” said Hilton.

“Really more accumulate over time, as the food settles on the floor. For example a piece of pasta settling after being dropped on the floor, it picks up bacteria as it melts into the floor, so to speak.”

Hilton said they wanted to find out the persistence of organisms on surfaces and their ability to transfer to food – as for bacteria to transfer to dropped food, they need to be on the floor material in the first place.

“Outdoor surfaces are completely different and present a different contamination risk. It depends on how clean the surface is to start with as well but we based it on typical findings with a normal hygiene routine.”

Who employs the rule?

The Aston team also carried out a survey of people who employ the five-second rule as part of a research project, the study is not peer reviewed.

277 females and 218 males responded to the survey given out through lectures and Facebook.

87% said they had or would eat food dropped on the floor with 55% female and 45% male.

81% of females said they had applied the “5 second rule” compared to 64% males.

Professor Hilton added: “Our study showed that a surprisingly large majority of people are happy to consume dropped food, with women the most likely to do so.

“But they are also more likely to follow the 5 second rule, which our research has shown to be much more than an old wives tale.” 

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