Chew on This

March 18, 2014

5-second rule may work, but hand-washing is better

Time for a confession: In my own kitchen I usually follow the five-second rule. This is the long-held belief that if food drops on the floor and is picked up within five seconds it is safe to eat. If it is a cut fruit or veggie I’ll wash it, and it is a hard food like almonds I’ll brush it against something.

Time for a confession: In my own kitchen I usually follow the five-second rule. This is the long-held belief that if food drops on the floor and is picked up within five seconds it is safe to eat. If it is a cut fruit or veggie I’ll wash it, and it is a hard food like almonds I’ll brush it against something.

Like many kitchen tales the origins of this belief are unknown. But ingenious biology students at Aston University in Britain did a bit of research on the practice and came up with, for me, reassuring results.

Researchers monitored the transfer of E. coli and Staphylococcus aureus from carpet, laminate and tiled surfaces to toast, pasta, biscuit and a sticky sweet. The times studied were from three to 30 seconds. Surprisingly bacteria were least likely to transfer from carpeted surfaces and most likely from laminate and tile. Sticky food, as expected, picks up the most bacteria. And time was a significant factor in the transfer of bacteria. The shorter the contact the better.

Their conclusion: “We have evidence that bacterial transfer from indoor flooring surface is incredibly poor.”

The best way to minimize the transfer of germs is washing your hands in soapy water before and after handling food and any items that can transfer bacteria. The myth here, surprisingly, is you don’t need hot water.

Amanda Carrico from the Vanderbilt Institute for Energy and Environment said that after a review of the scientific literature, her team found ‘no evidence that using hot water that a person could stand would have any benefit in killing bacteria.” Even water as cold as 40°F (4.4°C) appeared to reduce bacteria as well as hotter water, if hands were scrubbed, rinsed and dried properly. She says washing with hot water is unnecessary and wasteful. Washing with warm water can actually soften the upper layers of the skin, making you more vulnerable to germs.

Sheah Rarback is a registered dietitian on the faculty of the University of Miami Leonard M. Miller School of Medicine. Follow her on Twitter @sheahrarback

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