Scientists get to the truth behind the 'five-second rule'

We’ve all cried it, or at least heard it, when dealing with delicious food.

“Five-second rule!” – sometimes altered to three or 10 seconds, is used as a protective shield against accusations of poor hygiene.

Because, it suggests, as long as you rescue the treat within the appropriate time frame, it’s still perfectly fine to eat.

But is that really true?

Well, scientists have attempted to put the debate to bed – pointing out that it depends on a number of factors.

Firstly, the type of food in question.

“Wet” items, such as fruit chunks, creamy cakes and meats, attract bacteria faster than dry foods like crisps or dry toast.

So, essentially, the wetter the food, the less leeway you have.

If you drop food like watermelon on the ground, you're better off not trying to salvage it(iStock)

Next, where you drop it.

Although bathrooms and kitchens are home to the greatest quantity of bacteria – around 700 per square foot, the Daily Mail reports– no room in your house is safe.

At least 400 types of microscopic germs reside in your living room alone, according to research published earlier this year.

This sobering study also found that pavements host 30,000 bacterial cells per 100 millilitres of water, including faecal matter and E. Coli, which we then tread into our homes and transfer to any food we drop on the floor.

And whilst rinsing the food removes some of the visible particles like dirt or hair, it does little to remove the germs it collected on the floor, regardless of the amount of time it spent down there.

“Unfortunately, the five-second rule is a myth,” Dr. Wendi Lebrett, an internal medicine physician and gastroenterology fellow, told Food and Wine.

Sadly, rinsing food after you drop it does little to remove the germs(iStock)

Elsewhere, a Rutgers University study, conducted in 2016, examined four food types: watermelon, dry bread, bread with butter, and gummy sweets, which were tested on different surfaces that had been coated in a bacterium with characteristics similar to salmonella.

Their findings revealed that watermelon acquired the most bacteria after the five-second rule while the gummies had the least, and bread and bread with butter were the most variable of the group.

Interestingly, bacterial transmission from carpet was very low compared with tile and stainless steel, while transfer rates from wood varied.

The researchers ultimately concluded that the composition of the food and the type of surface onto which it lands matters as much – or more – than the length of time it spends on the floor.

In an interview, food microbiologist Professor Schaffner, who led the study, admitted: “I will tell you on the record that I’ve eaten food off the floor.”

But, he added: “If I were to drop a piece of watermelon on my relatively clean kitchen floor, I’m telling you, man, it’s going in the compost.”

Genghis Khan allegedly created a rule for banquets, stating: “If food was dropped on the floor, it could stay there as long as long as he permitted” (iStock)

So where did the “five-second rule” come from, if it’s clearly untrue?

There are various theories surrounding the saying, but many attribute it to the notorious Mongol ruler Genghis Khan, who declared that food could be on the ground for five hours and still be safe to eat, Professor Schaffner said.

And despite the mounting evidence showing how quickly bacteria adhere to food, food scientist Donald Schaffner, also of Rutgers University, acknowledged that the five-second rule will most likely endure.

“People really want this to be true,” he told National Geographic. “Everybody does this; we all eat food off the floor.”

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