Double-Dipping: A Proven Party Foul

by Ali Schumacher on November 28, 2012

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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).