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Hard Science

Why the “Five-second Rule” is Completely Bogus

One researcher called the rule an “oversimplification.”  
Sour candy spilled on the floor.

I remember one incident with an ice cream cone when I was a small child. Ecstatic to receive it, as soon as I brought it closer to my lips, it swayed then tumbled onto the ground with a plop. I looked up at my father with big eyes. He quickly yelled at me and refused to buy me another. I cried. Then, I pouted all the way home. By nature I’m a clumsy oaf. There’s no denying that. Since that time and with more suitable fare, I’ve cleverly evoked the “five-second rule.”

It’s a comforting thought. After all, it does take some time for bacteria to reach the food, once it’s fallen onto the floor, doesn’t it? Really, that begs the question: is there really such a window? And is it really safe to eat, in that timeframe? Fortunately for us, Rutgers University researchers have some answers.

In a recent study, Prof. Donald Schaffner—a food science specialist, attempted to find out. Schaffner found that bacteria can transfer to food in less than one second. But transfer depends on a number of factors, such as the surface it hits, how much moisture is found there, and how long the food makes contact for. Schaffner said that although the five-second rule is popular in our culture, actual, peer-reviewed research behind it was limited.

By: Greg WilliamsDerivative work: Pengo – Five second wikiworld.jpg, CC BY 2.5.

Even though the topic is considered “light,” the results could be useful, particularly since the practice is so widespread. According to the CDC, one in six Americans are sickened with some type of food borne illness each year, equaling around 48 million all told. 128,000 are hospitalized annually with such an illness, while 3,000 die from one.

Schaffner and graduate student Robyn Miranda decided to tackle the topic in his laboratory. Four surfaces were tested. These were wood, carpet, ceramic tile, and stainless steel. Four different foods were chosen: strawberry gummy candies, watermelon, plain white bread, and bread and butter. Lastly, four different contact windows were gauged—one second, five seconds, 30 seconds, and 300 seconds.

Researchers first grew a safe bacteria called Enterobacter aerogenes, a “cousin” of Salmonella. All the surfaces were then exposed to the bacteria. They were allowed to dry before the food was dropped, and left there for the aforementioned time periods. 128 scenarios in total were run. Each was repeated 20 times, totaling 2,560 measurements. The surfaces and the food were analyzed after each drop. The end result, gummy candies were the least likely to be contaminated, while watermelon was the most likely.

Bacteria racing across the floor to infect your food.

According to Schaffner, “Transfer of bacteria from surfaces to food appears to be affected most by moisture.” He went on, “Bacteria don’t have legs, they move with the moisture, and the wetter the food, the higher the risk of transfer. Also, longer food contact times usually result in the transfer of more bacteria from each surface to food.”

As for surfaces, stainless steel and tile had higher transfer rates than carpet. With wood, it depended on several variables. Schaffner said that the surface and the type of food were the most important factors in the amount of bacteria one might pick up. But the longer the food spent on the floor, the more likely it was to make contact with bacteria.

So in this sense, there is some truth to the five second rule. But Scaffner called it an “oversimplification” of the matter. “Bacteria can contaminate instantaneously,” he said. This research is sure to ruin childhoods and the social standing of clods everywhere. But at least we know the truth.

To see how the Myth Busters approached the subject click here: 


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