"You dipped the chip, you took a bite, and then you dipped again! That's like putting your whole mouth in the dip!"
These immortal words are from Season 4, Episode 19 of Seinfeld, way back in '93, which seared the concept of the "double dip" into our collective unconscious and has provided fodder for countless awkward conversations at catered events.
But are accusations of spreading harmful bacteria via double-dipping grounded in science, or just unquestioned post-Seinfeld common sense, like shrinkage and re-gifting?
It's a fair question given the implications that one can contaminate an entire party with overzealous dipping. In fact, it's such a valid concern that a team of researchers from Clemson University decided to take a closer look at the science of double-dipping.
Writing in Scientific American this week, Professor of Food Science and lead researcher Paul Dawson summed up an earlier article entitled "Effect of biting before dipping (double-dipping) chips on the bacterial population of the dipping solution."
The bottom line is that your mouth, and every human mouth, is a dirty, filthy cavity. Diseases like pneumonic plague, tuberculosis, influenza, disease, and severe acute respiratory syndrome (SARS) are all transmitted through saliva.
It's no surprise that the Clemson team found no detectable bacteria present in "solutions" which had not been dipped in, those solutions included salsa, cheese, and cheese dips and each of them appeared to be greatly affected by double-dipped chips.
"Once subjected to double-dipping, the salsa took on about five times more bacteria (1,000 bacteria/ml of dip) from the bitten chip when compared to chocolate and cheese dips (150-200 bacteria/ml of dip)," Dawson wrote. But salsa, with all of its fiery peppers and tomatoes, was also the quickest to kill bacteria. "Salsa is also more acidic. After two hours, the acidity of the salsa had killed some of the bacteria (most bacteria don't like acid)."
Acidity aside, it would appear that the threat level of double-dipping also depends on the viscosity of the solution involved.
"Chocolate and cheese dips are both pretty thick," the food scientist added. "Salsa isn't as thick. The lower viscosity means that more of the dip touching the bitten cracker falls back into the dipping bowl rather than sticking to the cracker. And as it drops back into the communal container, it brings with it bacteria from the mouth of the double-dipper."
Finally, the issue is not whether or not double-dipping spreads harmful bacteria—it most certainly does, and George Costanza is once again in the wrong. The real issue is how to control and minimize the effects of double-dipping by misanthropes attending parties.
Dr. Dawson concludes his article with some practical advice for the holidays. "If you detect double-dippers in the midst of a festive gathering, you might want to steer clear of their favored snack. And if you yourself are sick, do the rest of us a favor and don't double-dip."
Or, you can always just adhere to the brave, defiant words of George Costanza: "You dip the way you want to dip, and I'll dip the way I want to dip."