A study inspired by a Seinfeld episode finds that double-dipping -- using the same chip to dip twice -- does indeed transfer bacteria from the mouth of the double-dipper to other dippees.
But first, some history on the episode.
Peter Mehlman, a veteran “Seinfeld” writer, wrote the episode. “At the time I was living in Los Angeles, in Venice,” he told me. “There was a party on one of the canals, and apparently someone dipped twice with the same chip. And a woman flipped out. ‘You just dipped twice! How could you do that? Now all your germs are in there!’ I thought, this is just too good not to use on the show.”
Timmy’s line appears to have been the first notable use of “double dip” to mean dipping a chip twice. George has to ask Timmy what it means. Mr. Mehlman said he thought that it was an obvious name for the offense.
At the party, he had sympathized with the double dipper. “We get exposed to germs in a thousand different ways,” he said. “Besides, I thought the dip was enough to kill anything. It was probably one of those ’60s-style dips with artificial dried onion soup.”
Professor (Paul L.) Dawson told me that he had expected to find little or no microbial transfer from mouth to chip to dip, which would support George’s nonchalance. The results surprised him.
The team of nine (Clemson University) students instructed volunteers to take a bite of a wheat cracker and dip the cracker for three seconds into about a tablespoon of a test dip. They then repeated the process with new crackers, for a total of either three or six double dips per dip sample. The team then analyzed the remaining dip and counted the number of aerobic bacteria in it. They didn’t determine whether any of the bacteria were harmful, and didn’t count anaerobic bacteria, which are harder to culture, or viruses.
There were six test dips: sterile water with three different degrees of acidity, a commercial salsa, a cheese dip and chocolate syrup.
On average, the students found that three to six double dips transferred about 10,000 bacteria from the eater’s mouth to the remaining dip.
Each cracker picked up between one and two grams of dip. That means that sporadic double dipping in a cup of dip would transfer at least 50 to 100 bacteria from one mouth to another with every bite.
As to the actual dangers of double-dipping?
Professor Dawson and his team write that the actual risks of double dipping are “debatable” and depend on many unknowable factors.