Dip once or dip twice?

OUR annual national snacking binge is almost here. It would take a very large bowl indeed to hold all the guacamole mashed from the more than 100 million avocados that are consumed on Super Bowl Sunday. (My rough calculation gives a hemisphere bowl 20 yards in diameter and 3 times the height of the goal post crossbars.) And guacamole is just one of many dips that will be shared around the TV.

Just in time, a scientific report has some new findings that may cause football fans to take a second look at that communal bowl of dip.

The study, to be published later this year in the Journal of Food Safety, is the only one I’ve ever seen to proclaim that it was inspired by an episode of “Seinfeld.” It was conducted as part of a Clemson University program designed to get undergraduate students involved in scientific research. Prof. Paul L. Dawson, a food microbiologist, proposed it after he saw a rerun of a 1993 “Seinfeld” show in which George Costanza is confronted at a funeral reception by Timmy, his girlfriend’s brother, after dipping the same chip twice.

“Did, did you just double dip that chip?” Timmy asks incredulously, later objecting, “That’s like putting your whole mouth right in the dip!” Finally George retorts, “You dip the way you want to dip, I’ll dip the way I want to dip,” and aims another used chip at the bowl. Timmy tries to take it away, and the scene ends as they wrestle for it.

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 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 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.

The kind of dip made a difference in a couple of ways. The more acidic water samples had somewhat fewer bacteria, and the numbers of bacteria declined with time. But the acidic salsa picked up higher initial numbers of bacteria than the cheese or chocolate, because it was runny. The thicker the dip, the more stuck to the chip, and so the fewer bacteria were left behind in the bowl.

Professor Dawson said that Timmy was essentially correct. “The way I would put it is, before you have some dip at a party, look around and ask yourself, would I be willing to kiss everyone here? Because you don’t know who might be double dipping, and those who do are sharing their saliva with you.”

Professor Dawson encourages his undergraduate teams to test popular conceptions about food safety in the laboratory. Last year he published a paper on the five-second rule, which states that food dropped on the floor can be safely eaten if you pick it up before you can count to five. The rule turned out to be false.

I asked Mr. Mehlman what he thought of Professor Dawson’s study on double dipping. “It’s pretty gratifying to know that 15 years later the show continues to exist on the cultural landscape,” he said. “But it reminds me of Jerry’s joke about the scientists who developed the seedless watermelon.”

That stand-up joke opened a “Seinfeld” episode in 1994: “These guys are going, ‘No, I’m focusing on melon. Oh sure thousands of people are dying needlessly. But this,’ ” and here Mr. Seinfeld made a spitting noise, “ ‘that’s gotta stop. You ever try to pick a wet one up off the floor? It’s almost impossible. I’m devoting my life to that.’ ”

As Mr. Mehlman implied, double dipping appears unlikely to be a major public-health threat. Professor Dawson and his team write that the actual risks of double dipping are “debatable” and depend on many unknowable factors.

But it’s good to be aware that sharing a bowl of dip can mean sharing more than we’d like. And happily, the obvious preventive measure requires no deprivation, just a newly focused snack category: one-dip chips, too small for two.

Tomado del New York Times.