Scientists Test 3-Second Rule on Dropped Foods

Scientists Test 3-Second Rule on Dropped Foods

Food & Drink

Scientists Test 3-Second Rule on Dropped Foods


We’ve all done it…accidently dropped some food on the floor, picked it up quickly, brushed it off and eaten it. As long as it’s retrieved within the “three-second rule,” we figure (hope) it’s safe to eat.

The time interval of the rule seems to vary depending on what part of the world you live in. I’ve heard 5-second and 10-second versions of the rule, too.

But I’ve always considered it to be a “wink, wink” kind of deal with probably zero factual data to back it up.

Well, a team of researchers in the U.K. decided to put the “rule” to the test with some real science.

Five food items were tested by Manchester Metropolitan University (MMU) to see whether the x-second rule could be trusted.

Bread with jam, cooked pasta, ham, a plain biscuit and dried fruit were all dropped on the floor and left for either three, five or 10 seconds, then examined under the microscope.

These items were selected as commonly eaten foods and because all have different water activity levels–a key factor in whether items will sustain bacterial growth in the few seconds before they are picked up from the floor.

After being picked up from the floor, the foods were examined to determine whether or not harmful bacteria found on the floor was then found to be growing on the dropped food.

The study revealed that dropped foods with a high salt or sugar content were safer to eat after being retrieved, because there is less chance of harmful bacteria surviving on such items.

Eating processed food from the floor poses the lowest risk due to the fact that it generally contains such high levels of sugar and salt.

The ham, a salty product, and the sugary bread and jam also fared well in the test. When retrieved from the floor within three seconds, the foodstuffs showed little sign of bacterial growth.

The dried fruit and cooked pasta, on the other hand, showed low levels of klebsiella after three seconds — a bacteria which can potentially lead to a wide range of diseases such as pneumonia, urinary tract infections, septicaemia and soft tissue conditions. The biscuit and bread and jam showed no bacterial growth after their time on the floor, which can be linked to the high sugar content of the jam which makes it unlikely to support microbial growth.

The researchers said they only embraced the three second rule when at home, with all admitting they would discard anything dropped on the floor when out in public. (Yeah, gotta go along with that.)

Well, there you have it. The three-second rule now has some scientific backing. Guess we’d better avoid trying to retrieve that dropped spaghetti or dried fruit. 

Of course, the research team doesn’t know how clean I keep my kitchen floor. We’ll not get into that here.

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