TORONTO - All you double-dippers, back away from the chip dip bowl.
Seems the famous Seinfeld episode was right - double-dipping does transfer mouth microbes from bitten chips or vegetables into the dip. After multiple double-dippers, what might look like an enticing snack may actually be a microbial soup, a new study suggests.
The research, by food science students at Clemson University in Clemson, S.C., found that for every time a bitten cracker went back into the bowl, hundreds, even thousands of bacterial cells went in with it.
"In the real world, if you have a dip there, you're probably going to have more than one person dipping into that dip bowl," says Paul Dawson, the food sciences professor who oversaw the project.
"It could be a big party. You have a lot of people dipping. So every time someone dips they're inoculating that many cells into the dip."
The research was done under Clemson's creative inquiry program, which teaches undergraduates how to conduct research while encouraging outside-the-box thinking.
Teams made up of students at various points in an undergraduate degree set out to explore interesting ideas, often producing scientific journal-worthy results in the process.
(An earlier effort by Dawson's students tested the five-second theory - the notion that no significant transfer of germs occurs if dropped food is retrieved immediately. Their conclusion? You may move fast, but microbes move faster.)
This latest project was inspired by the famous Seinfeld double-dipping episode, where George blithely turns a chip dip into a Petri dish, to the revulsion of a fellow party-goer.
"Did you just double-dip that chip? You double-dipped the chip!" the disgusted character, Timmy, declared.
"That's like putting your whole mouth right in the dip."
Not quite, maybe, but the research Dawson's students performed suggests a dip bowl will acquire much more than salsa chip crumbs as a social event progresses.
The average human mouth is teeming with bacteria, though to be honest that's not as nasty as it sounds.
"Most of the bacteria - 99 per cent of bacteria - are good. It is normal flora," says Dawson, who noted these useful bacteria help keep the mouth healthy and defend against bad bugs.
"The normal bacteria are not going to make somebody sick. It's just kind of the yuck factor."
Still, that doesn't mean there aren't unpleasant germs you might pick up from fellow dippers who break party etiquette and go back for seconds with a bitten chip.
"It's not going to cause the plague probably, but the fact of the matter is ... if there was somebody in the room had that (a contagious disease) who was double-dipping, it's a pretty high risk that it's going to be transferred to other people if they're going to be eating out of that bowl," he says.
Dawson's students tested dips of different pH levels - a cheese dip, a chocolate dipping sauce and salsa.
"The two factors that affect the amount of bacteria in two words are the consistency of the dip and the acidity of the dip," Dawson notes.
While it might seem that the more acidic salsa would harbour fewer bacteria, in actual fact it contained more in the double-dipping experiment the Clemson students conducted.
However, when the students let inoculated dips sit at room temperature for a couple of hours to see whether passage of time influenced concentration of microbes, they found the salsa's bacterial count declined, putting it on about a par with the chocolate and cheese.
The double-dipped dips contained about 400 to 500 bacterial cells per millilitre - which is a tiny amount of dip, far less than would coat the average dipped chip. The team did not type the bacteria, so they don't know what dippers were leaving behind.
The students also didn't test heated dips. But Dawson suggests hot dips might provide ideal conditions for microbial growth. And he notes that as a party goes on and the amount of dip in a bowl declines, the microbe content of what remains would be expected to rise.
All this new-found knowledge has made Dawson approach the practice of dipping with a new level of caution. He might share a dip in a restaurant, where he can keep an eye on the people he's eating with. But at a party? That's another matter.
"I probably would avoid the dip bowl. I would pass on that."
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