Double-Dipping: A Proven Party Foul

by Ali Schumacher on November 28, 2012

Image courtesy of photopin.com

With the holiday season kicking off, the time has come to begin penciling in the holiday parties, potlucks, and get-togethers.  Time to pull the ugly holiday sweater out of storage and start to perfect your favorite party recipes.  However, while mingling through the festive atmosphere enjoying the holiday snacks, it may be beneficial to pay close attention to certain party etiquette.  Research suggests that “double-dipping” your snacks (i.e. chips in salsa, crackers in cheese dip) is, in fact, more than just a social faux paus.  It is indeed a great way to spread some germs this holiday season.

Intuitively, we all can guess that dipping a chip or cracker after taking a bite might not be the most sanitary practice.

A study from Clemson University took it one step further however, scientifically putting the “double-dip” on trial in 3 separate experiments.

In the first experiment, subjects wearing sterile gloves dipped crackers into sterile solutions of water.   There were four experimental groups: 3 dips without biting, 6 dips without biting, 3 dips with biting, and 6 dips with biting.  Each cracker was dipped into the sterile water at a depth covering the bitten surface, held there for 3 seconds, then discarded.

What did they find?

  • Higher populations of bacteria were found for solutions dipped with bitten crackers compared to whole crackers
  • A significant amount of the transfer of bacteria was attributable to double-dipping
  • There was no significant difference in the amount of bacteria found in the 6 double-dips condition as compared to the 3 double-dips condition

In the second experiment researchers used 3 types of commercial dips: salsa, chocolate dip, and cheese dip.  Each dip’s pH level was tested and replicated in a water-based solution.  Salsa had an average pH of 4, chocolate dip 5.1, and cheese dip 6.1.  Subjects were then given 9 plates of solution (3 of each pH level) and provided different dipping instructions for each plate: a “no dip” condition, “no bite” condition, and “double-dip” condition.

What did they find?

  • Bacteria levels were consistently higher in the double-dip condition compared to the control (“no dip”) and “no bite” conditions for all 3 pH levels
  • There was no statistically significant difference between the “no dip” and “no bite” condition
  • Bacteria levels in the “bite” condition plates were higher among the solutions with a higher pH (i.e. the bacteria levels would have been higher in the cheese dip than the more acidic salsa)

In the final experiment researchers used the actual dips for testing (as opposed to pH water solutions).  Subjects followed the same protocol as in experiment 2.  However, in addition to measuring bacterial levels, the researchers also looked at viscosity of the dips and the amount adhering to the cracker after dipping.

What did they find?

  • Bacteria levels were consistently higher in the double-dip condition compared to the control (“no dip”) and “no bite” conditions for all 3 dips
  • Immediately after exposure to a “double-dip,” salsa had higher levels of bacteria than the other 2 dips
  • However, 2 hours after, the “double-dip” levels of bacteria in salsa returned to being similar to those in the chocolate and cheese dips

Researchers hypothesized that the initial increase in bacteria within the salsas was due to the less viscous nature of the dip.  Simply put, more dip (and hence more of the contaminating bacteria) sticks to each cracker and is removed from the chocolate and cheese dips with each swoop.  The eventual leveling out of bacterial levels in the salsa was attributed to the acidic/antimicrobial nature of the dip.

So, looks like “double-dipping” is more than just a social taboo.  The studies demonstrated that majority of the bacteria found in our holiday favorites was a direct result of “double-dipping.”  Dips should not be feared altogether! Interesting findings in the studies showed that there was little to no difference between the “no dip” and “no bite” conditions.  Keep dipping, but with colds and flu going around, perhaps refraining from that second-dipped bite is the best way to spread some joy (and not germs).

Kurt November 28, 2012 at 3:26 pm

I have a problem with the experimental design. Holding a dip for 3 seconds? That’s a very long time. Who keeps the chip in the cheese for 3 seconds? It would only result in a soggy nacho chip. These results are likely valid, but their applicability to the real world of dipping is very questionable.

Great blog.

Ali Schumacher November 28, 2012 at 3:57 pm

Good point. I had the same reaction. It would be interesting to see if the amount of bacteria decreased at all depending on the amount of time it took to dip the contaminated cracker. Future research?

Peter November 28, 2012 at 4:21 pm

I scoop around. Sometimes I don’t want a chunk of salsa, or need to get just the right amount of dip. I’m fine with 3 seconds.

Kurt November 28, 2012 at 4:19 pm

Let’s do it. Shocked no one has done it already. It would be an easy experiment I think. We just need to find someone with a micro lab. It could lead to a revolution in the dip world. What if double dipping was OK as long as the dip lasted less than a second? Think of how many half-chips wouldn’t have to go undipped!

Ali Schumacher November 28, 2012 at 4:43 pm

Done. I’ll start gathering supplies. Wheat Thins or Triscuits?

Kurt November 28, 2012 at 5:13 pm

Clearly Triscuits. The future is bright.

Ashley November 28, 2012 at 4:32 pm

This was great! The double-dip thing has always grossed me out (unless I’m eating out of my own personal container of dip!). A lot of people say the solution to double-dipping without germs is to “flip-and-dip”–where after the first bite, you flip the cracker/chip around and put the not bitten end back in for the second dip. I’ve always been weary of this though since the not bitten end getting dunked is the end that was in your hand! I wonder if that has ever been studied…

Anyway, thanks for another interesting and easy to read post!

Ali Schumacher November 28, 2012 at 4:44 pm

Thanks Ashley! I must admit, I am a “flip-and-dip” kind of girl– I only do it with people I know well though. I would be very interested in seeing some research on this.
Thanks again for your comment!

Becky November 28, 2012 at 5:31 pm

An interesting topic, but does make me wonder – when you say there were higher levels of bacteria following ‘double dipping’ were these increases to a high enough level to actually spread diseases?

opurt November 29, 2012 at 9:19 am

Actually Myth Busters did this experiment. They found that you did get some contamination from double dipping, but it was minor compared to the bacteria already in the dip to start with. Think about that one for awhile.

Jon November 29, 2012 at 4:23 pm

Well, remember, Mythbusters are special FX experts, not science experts. While interesting, those test aren’t definitive, and aren’t they claimed to be. That said, it would be interesting to see the background bacteria in the test. Unfortantely, you have to purchase the article directly. Sad.

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