5 second rule: Is it true?

Editor’s note: The opinions expressed in this commentary are solely those of the authors. CNN features the work of The Conversation, a collaboration between journalists and scholars to provide analysis and commentary on the news. Content is produced solely by The Conversation.

When you drop a piece of food on the floor, is it really good to eat it if you pick it up within five seconds? This urban food myth claims that if food only spends a few seconds on the floor, dirt and germs won’t have much chance of contaminating it. The research in my lab has focused on how food and food contact surfaces become contaminated, and we worked on that particular wisdom.

Although the “five-second rule” may not seem like the most pressing issue for food scientists, it’s still worth investigating food myths like this because they shape our beliefs about the when food is safe to eat.

So is five seconds on the ground the critical threshold that separates an edible morsel from a case of food poisoning? It’s a little more complicated than that. It depends on how much bacteria can go from soil to food in seconds and how dirty the soil is.

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– Source: CNN

‘Julia’ goes beyond the kitchen with Julia Child

Wondering if food is still good to eat after being thrown on the floor (or anywhere else) is a fairly common experience. And that’s probably not new either.

A well-known, but inaccurate, story about Julia Child may have contributed to this food myth. Some viewers of his cooking show, “The French Chef,” insist they saw Child drop a lamb (or chicken or turkey, depending on which version of the tale) on the floor and pick it up, with the advice that if they were alone in the kitchen, their guests would never know.

Actually, it was a hash brown, and it fell on the stove, not the floor. The child puts it back in the pan saying “But you can always pick it up and if you’re alone in the kitchen, who’s going to see?” But the little-known story persists.

It’s harder to pin down the origins of the oft-cited five-second rule, but a 2003 study reported that 70% of women and 56% of men surveyed were aware of the five-second rule, and that women were more likely than men. men from eating food that has fallen on the floor.

So what does science tell us about what a few moments on the floor mean for your food safety?

The first research report on the Five Second Rule is attributed to Jillian Clarke, a high school student participating in a research apprenticeship at the University of Illinois. Clarke and her colleagues inoculated floor tiles with bacteria, then placed food on the tiles for varying lengths of time.

They reported that bacteria transferred from the tile to the gummy bears and cookies in five seconds, but did not report the specific amount of bacteria that transferred from the tile to the food.

But how many bacteria are actually transferred in five seconds?

In 2007, my lab at Clemson University published a study—the only peer-reviewed journal article on this topic—in the Journal of Applied Microbiology. We wanted to know if the length of time a food is in contact with a contaminated surface affects the rate of transfer of bacteria to the food.

To find out, we inoculated squares of tile, carpet or wood with Salmonella. Five minutes later, we placed either bologna or bread on the surface for five, 30 or 60 seconds and then measured the amount of bacteria transferred to the food. We repeated this exact protocol after the bacteria had been on the surface for two, four, eight and 24 hours.

We found that the amount of bacteria transferred to either type of food did not depend very much on how long the food was in contact with the contaminated surface – whether for a few seconds or for a whole minute. The overall amount of bacteria on the surface mattered more, and this decreased over time after the initial inoculation. It seems that what’s at issue isn’t how long your food languishes on the floor and much more how bacteria-infested that patch of soil is.

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We also found that the type of surface also made a difference. Carpets, for example, seem to be slightly better places to put your food than wood or tiles. When the carpet was inoculated with Salmonella, less than 1% of the bacteria were transferred. But when food came in contact with tile or wood, 48-70% of bacteria were transferred.

Last year, a study from the University of Aston in the UK used nearly identical settings to our study and found similar results when testing contact times of three and 30 seconds on similar surfaces. They also reported that 87% of respondents would eat or have eaten food that fell on the floor.

From a food safety perspective, if you have millions or more cells on a surface, 0.1% is still enough to make you sick. Also, some types of bacteria are extremely virulent and it only takes a small amount to make you sick. For example, 10 or fewer cells of a particularly virulent strain of E. coli can cause severe illness and death in people with weakened immune systems. But the likelihood of these bacteria being on most surfaces is very low.

And it’s not just dropping food on the floor that can lead to bacterial contamination. Bacteria are carried by a variety of “mediums,” which can include raw foods, moist surfaces where bacteria has been left, our hands or skin, and coughs or sneezes.

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Hands, food, and utensils can carry individual bacterial cells, colonies of cells, or cells living in communities contained in a protective film that provides protection. These microscopic layers of deposits containing bacteria are called biofilms and are found on most surfaces and objects.

Biofilm communities can harbor bacteria longer and are very difficult to clean. Bacteria in these communities also have increased resistance to disinfectants and antibiotics compared to bacteria living alone.

So, the next time you consider eating a scrapped food, the odds are in your favor that you can eat that morsel and not get sick. But in the rare case where a microorganism can make you sick at the exact spot where the food has fallen, you can be pretty sure the bug is on the food you’re about to put in. your mouth.

Research (and common sense) tells us that the best thing to do is to keep your hands, utensils, and other surfaces clean.


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