You’ve probably heard of the five-second rule: if you pick up food that has fallen on the floor within five seconds, the food is not yet contaminated with bacteria. But is that correct? Two microbiologists provide the answer.
If you still want to eat food that has fallen on the floor, there are a number of things you should take into account, according to food microbiologist Gerrieke van Middendorp of Wageningen University. The type of floor is one of those factors. It depends on how much surface area of the floor has come into contact with the food. With a smooth surface there is greater contact with the food than with a carpet. In principle, on a smooth floor, more bacteria from the floor come into contact with the food.
Of course, it is not only the type of floor that matters. In general, a smooth floor is cleaned more often and easier than a carpet. That old Persian carpet will most likely contain more bacteria than those smooth kitchen tiles.
A tenth of a second
Furthermore, the type of food that falls to the ground is important. This has to do with how bacteria move. “Bacteria cannot fly, walk or jump,” says Gerrieke. “They are mainly dependent on air and water flows for their transport. Therefore, if you drop wet food, bacteria on the floor are easily able to move to the food. A piece of watermelon contains many bacteria within one tenth of a second. On the other hand, if you drop a dry sandwich, only a small part of the bacteria has been transferred in the same time.”
What exactly you spill on the floor is more important than how long it stays there.
We know all this thanks to the efforts of scientists at Rutgers University in the US, who dropped different types of food on different types of floors in an experiment. They left the food there for one second to five minutes and then looked at how much bacteria was on it. What exactly you spill on the floor is more important than how long it stays there, the scientists decided.
So: what is true about the five-second rule? “In any case, this does not apply to wet food,” Gerrieke emphasizes. You can never pick up that dropped food in a tenth of a second. With dry food it may be worth picking it up quickly, but even then there will already be some bacteria on it. “There is also no point in rubbing or blowing on the picked up food, as many people do. That doesn’t get rid of the bacteria,” adds food safety expert and microbiologist Liesbeth Jacxsens from Ghent University.
Millions of species of bacteria
It is therefore not possible to completely prevent bacteria from getting on your food when you drop something. How bad is that? According to the microbiologist, that isn’t too bad. “A lot of bacteria are good. Only a small amount can actually make you sick. There are millions of types of bacteria, but only about a hundred can cause illness in your intestines. This also applies to bacteria on the ground: there is a small chance that the spot where you dropped your food just happens to have so many ‘bad bacteria’ that it will immediately make you ill.”
However, according to Jacxsens, the chance is greater if you do not take off your shoes in your house: bacteria in feces easily find their way inside. Whether you get sick, on the other hand, depends not only on the bacteria that hitched a ride, but also on your own immune system. “A healthy adult can handle something,” says Jacxsens. “But with small children, pregnant people, the elderly and people with a weakened immune system, it is better to be more careful.”
Just pick it up and throw it in the trash bin.
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