18 July 2014

Food from the Floor

Popcorn on floor (carpet and tile)
and counter from overachieving
hot-air popcorn maker. Bowl
is actually a plastic cake carrier.
Welcome back. It keeps happening. Our…ok, my hot-air popcorn popper overachieves and sends popped corn bouncing out of the bowl. Most of the strays end up on the counter, but a few reach the floor, where I grab and blow on them, then eat them.

It’s not like I don’t find them right away. They’re down there only about 10 seconds. And it’s not like the popcorn is buttered or greasy or covered with honey mustard. I take my popcorn straight. My quick huff and puff is to remove dust or whatever, not germs. Blowing, I probably add germs. Anyway, our kitchen floor isn’t that bad now that we have no cats.

Although I’ve retrieved popcorn from the floor on countless evenings, last night was the first time I remember hesitating. I had just read about research on the topic, specifically, tests of the 5-second rule: If food that falls to the floor is in contact with the floor for fewer than 5 seconds, it’s safe to eat. What do you think?

Initial 5 Second Rule Studies

I’d be surprised if someone didn’t run a test before 2003; however, that summer, a high school student in an apprentice science program at the University of Illinois at Urbana-Champaign conducted a well-controlled study. After finding university floors too clean, she procured new smooth and rough ceramic floor tiles, sterilized and inoculated the tiles with Escherichia coli (E. coli) bacteria, placed measured samples of cookies or sticky candy on the tiles and determined that the bacteria contaminated the samples in no more than 5 seconds. (More bacteria hopped to the sticky candy from the smooth tiles than from the rough tiles.)

A few years later, Clemson University researchers published results of a study that confirmed Salmonella Typhimurium bacteria can (1) survive for up to four weeks on dry tile, wood and carpet in sufficiently high populations to be transferred to bologna, and (2) be transferred almost immediately on contact.

Over 99% of the S. Typhimurium cells were transferred from tile to bologna in 5 seconds, though transfer from carpet was very low compared with that from wood and tile. How long the bacteria sat around on the surfaces before the food was delivered was an important factor in the transfer.

Moving Forward

This Minnesota 5th grader tested the
 5-second rule with a candy bar and
 banana  for her science fair project.
Tests of the 5-second rule have since been reported by others and the topic is now a common grade school science project. Nevertheless, a researcher from England’s Aston University recently added his students’ findings. I was surprised to see news releases and interviews on the work before the paper was accepted, but the study was rather straightforward.

In a class project, the students monitored the transfer of E. coli and Staphylococcus aureus bacteria from several floor types, including carpet, wood laminate and tiles, to toast, pasta, biscuit and a sticky dessert. The food samples were in contact with the floor types for 3 to 30 seconds.

The results confirmed that time is a significant factor in the transfer of bacteria--the longer the contact, the greater the contamination. Further, the study demonstrated the significance of both the floor type and the food’s moisture content. Bacteria were least likely to transfer from carpeted surfaces, and probably because moist foods make better contact with the surfaces, they’re more easily contaminated.

Wrap Up

Unlike the earlier studies, which saw any bacterial transfer as a red flag, the Aston study seemed to treat its findings as a validation that retrieving dropped food quicker than 5 seconds is generally an acceptable risk.

Me? I lean toward the Clemson lead author’s comparison of eating dropped food with not wearing a seatbelt. But I’ll accept the risk for popcorn. As my mother used to say, You have to eat a peck of dirt before you die. Just watch out for those E. coli and staph. Thanks for stopping by.


-High school student study at University of Illinois:
www.npr.org/templates/story/story.php?storyId=1437387 (listen to the interview)
-Clemson study in the Journal of Applied Microbiology:
-Aston University news release:
-Example articles on the Aston University study:
-Daily Mail article on another university test of dropped food rule:
-Suggested protocol for middle school science project on the 5 second rule: www.education.com/science-fair/article/to-eat-or-not-to-eat-5-second-rule/

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