Although eating from communal bowls has probably been around for ever, the first reference to ‘double-dipping’ seems to have come from a 1993 Seinfeld episode in which the legendary George Constanza is berated after he dips the same chip twice at a gathering after a funeral. His girlfriend’s brother, Timmy, asks, ‘Did you just double-dip that chip?’ Timmy claims that the offence of double-dipping is ‘like putting your whole mouth right in the dip’. George doesn’t think it’s such a big deal. (Of course, he also eats out of the dustbin in another episode.) ‘You dip the way you want to dip, I’ll dip the way I want to dip,’ he snapped. And if you know George, you know what happened next – they end up wrestling over the contaminated chip. At the funeral.
Salsa. Guacamole. Hummus. Whether you dunked in a spicy or sweet or creamy dip, whether you used a crisp or a cracker or a vegetable, we bet that you have been a double-dipper too. You wanted just a bit more of something on the rest of your crisp, and so you plunged it back into the dip a second time. Sticking a crisp back into the bowl of dip doesn’t seem like a big thing, right? You might argue that we are exposed to small amounts of germs all the time.
Once again, the food scientists want to ruin our fun – and it seems they side with Timmy on this one. One intrepid group of microbiologists, led by Dr Paul Dawson, studied whether or not bacteria were really transferred from mouth to chip to dip (the double-dipping scenario). Volunteers took a bite of a wheat cracker and then dipped the cracker for three seconds into a tablespoon of a test dip. They used six different dips: salsa, cheese dip, chocolate syrup, and sterile water with three different acidity levels. The scientists compared the double-dips to what happened when a brand-new cracker was dipped, and they measured the amount of bacteria in the volunteers’ mouths. And the results were not pretty.
On average, three to six double-dips transferred about 10,000 bacteria from the eater’s mouth to the dip. And each cracker picked up between one and two grams of dip. If you are at a party and three to six people double-dip their chips, any chip you dip may pick up at least 50 to 100 bacteria. Could this make you ill? Maybe. It depends on how many bacteria you pick up in your bite, how many people are double-dipping and what bacteria they have in their mouths. This study only looked for some types of bacteria, and other kinds of bacteria might have been in the dip. The risk to you might depend on whether the bacteria in the dip are the kind that can make you really ill or a less harmful variety. However, the study revealed that bacteria can be transferred and that the dip does not kill off all of the bacteria.
For the germ-phobes and paranoid folk out there, it may be helpful to know that some kinds of dips are less likely to harbour bacteria. The more acidic water samples had less bacteria and the number of bacteria in them got smaller over time. But acidity is not everything. An acidic salsa sample picked up more bacteria than the cheese or chocolate dips. This is probably because it was runny. The thicker the dip, the more of it sticks to the chip, which can act to seal in the bacteria. So fewer bacteria are left behind in the bowl. Thus thicker dips may be safer after double-dipping than thinner dips.
The next time you are at a party and considering a plunge into the dip bowl, Dr Dawson suggests you take a look at the people around you. Would you kiss them? Would you ever want to lick the insides of their mouths? If you don’t want to swap spit with these people, then think twice before helping yourself to the dip.