Sometimes the NY Times can be a very useful publication and today is one of those days. Just in time for the Super Bowl party near your home, they provide us with a lengthy article about recent research into double dipping. That is, of course, when you take your chip or pita slice and after taking a bite, proceed to re-introduce it to the dip along with your friendly germs. A researcher actually wanted to explore whether double dippers were indeed sharing their germs with others. In a word: yes. In fact, he likens it to kissing everybody else at the party. With your tongue.
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.
Enjoy your party!
