Double Dip Chip Challenge

Jack Spangler turns double-dipped chip dip into Petri pudding.

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You’ve seen it… someone takes a potato chip, dips it in the chip dip, bites off part of the chip, and then proceeds to dip the chip again. Yes, this is the socially unacceptable act of double-dipping. While some people think it’s no big deal, others believe the act of double-dipping is the same as putting your whole mouth into the bowl of dip. Is this true or just a myth? Leave it to a fifth grader armed with Petri dishes, chips, dip, and an aversion to double-dipping your chip to uncover the truth. 

Here's What You'll Need

  • Petri Dishes
  • Nutrient Agar
  • Cotton swabs
  • Potato chips
  • Dip
  • Bad manners


Submitted by Jack Spangler

The young experimenter for this project is none other than Jack Spangler. After seeing an episode of Mythbusters, Jack didn’t necessarily see eye-to-eye with the show’s conclusion – double-dipping is no big deal. So, he set out to perform his own version of the Double-Dip Chip Challenge.

  1. Purchase a sixteen ounce carton of Ranch dip from the store.
  2. Purchase a bag of potato chips.
  3. Prepare three Petri dishes with nutrient agar (using the technique described in the kit instructions). Allow the liquid to harden in the Petri dishes overnight. Keep the Petri dishes covered so that bacteria cannot get into the agar.
  4. Divide the Ranch dip equally into three clean bowls.
  5. Label the first bowl “plain dip.” Label the second bowl “DOUBLE-DIPPED.” Label the third bowl “LICKED THE WHOLE THING.”
  6. Get a large chip and dip it into the “plain dip” bowl. Only dip the chip once. This will be the “control.”
  7. Get a large chip and dip it into the “DOUBLE-DIPPED” bowl and put the chip into my mouth. Bite it in half. Then dip the chip again into the bowl. I have successfully completed the double-dip.
  8. Pick up the third bowl labeled “LICKED THE WHOLE THING” and do what the label says – lick the whole thing! I will poke my tongue into every nook and cranny of the bowl. Do lots of licking until my Mom is totally grossed out.
  9. Use a clean cotton swab to swab a sample of the “plain dip.” Smear this onto the first Petri dish and label it “plain dip.”
  10. Use a clean cotton swab to swab a sample of the “DOUBLE-DIPPED” dip. Smear this onto the second Petri dish and label it “DOUBLE-DIPPED.”
  11. Use a clean cotton swab to swab a sample of the “LICKED THE WHOLE THING” dip. Smear this onto the third Petri dish and label it “LICKED THE WHOLE THING.”
  12. Place the Petri dishes in a place that is between 75oF and 80oF for two days. Watch for the bacteria to grow.
  13. Compare the amount of bacteria that has grown on each of the samples.

How Does It Work?

The hypothesis was easy to prove – my double-dipped bowl of dip had less bacteria than the “whole mouth” bowl. But I was surprised to see how much bacteria was really in the double-dipped bowl. If you think about it, the chip just touches your mouth for a split second before you plunge back in and get some more dip.

I was really surprised to find how much bacteria there was in the “plain dip” Petri dish. When I read more about bacteria in food, I discovered that there is a lot of good bacteria in food. I wonder if there would have been as much bacteria if I would have used salsa instead of a sour cream kind of dip?

Double-dipping your chip is not a good idea. Some people would say it’s not that big of a deal, but my tests show that the bacteria from my mouth still grew… and it’s gross!

Additional Information: Food science students at Clemson University examined the effects of double-dipping using volunteers, wheat crackers, and several sample dips. They found that three to six double dips in one bowl transferred about 10,000 bacteria from the eaters’ mouths to the remaining dip. That means if you’re at a party and three to six people double-dip their chips, any chip you dip may pick up at least 50 to 100 bacteria. The research was published earlier this year online in the Journal of Food Safety.

Additional Info

Science Fair Connection:

What could be better than grossing out your parents, friends, and teachers at the science fair? The Double Dip Chip Challenge clearly follows the requirements of an effective science fair project. It uses a control (the dip with the single dipped chip) and then changes a variable (the double dipped chips), runs some tests under standardized conditions, and then makes comparisons of the results.

If you’d like to try this experiment for your own science fair project, don’t take Jack Spangler’s word for it. Do the same thing and see if you can validate his results. Or, if you want to change it up a bit, consider the following variations:

  • Change the type of dip to a non-creamy based dip (like salsa) and see if you get the same results. Do everything else the same.
  • Change the type of chip but keep everything else the same.
  • Change the person who double dips the chips. If the results are different, what might that indicate about that particular person’s mouth? Ew, that could be gross!
  • If you like the growing bacteria idea but want to do something altogether different, try finding germy places in your house and then test the germ-killing effectiveness of different household cleaners. See our Growing Bacteria experiment or our Bacteria Growing Kit for more information and ideas.

The Double Dip Chip Challenge follows the scientific method, isolates and controls variables, documents discoveries, and teaches a real world lesson about food safety and the spread of germs. It is sure to be a favorite at the science fair!

Jack used Comic Life to present his science fair project…


Plain Dip – After three days, I noticed that there were some things growing. This could be from the good bacteria in the dip, but I’m not really sure.

Double-Dipped – The double-dipped dish didn’t look as bad as the plain dip until I started to count all of the bacteria colonies. There are at least 28… maybe more.

Licked the Whole Thing – This is just one giant, disgusting dish of Petri pudding. There are so many colonies that they started to fuse together.

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