How Bad Is Double-Dipping?

With a little more couch time than normal this flu season, I binge-watched some new TV series and rewatched some classics. After seeing George Costanza double-dip a chip during a wake, I started to wonder – is it really “like putting your whole mouth right in the dip!” Here’s the scene from a 1993 episode of Seinfeld for those who may not be familiar with it:

Turns out I’m not the only one who wondered whether bacteria in your mouth can make it onto the chip then into the dip. Clemson Professor Paul Dawson is a food scientist who researches how common food habits can increase the spread of bacteria and was inspired by watching that episode. His undergraduate research team designed a series of experiments to find out how bad double-dipping really is.

The first experiments compared how much bacteria were transferred from a cracker to a cup of water when it was either bitten or unbitten. Not surprisingly, the researchers found bitten crackers transferred “about 1,000 more bacteria per milliliter.” Then they varied the pH level of the water to be increasingly acidic, measuring the bacteria levels right after dipping and again two hours later. The more acidic water initially tested with high levels of bacteria but they dropped over time. Most bacteria can’t survive in acidic solutions.

But would the results stand up to real life? The second experiments replaced the water with three kinds of dip: chunky salsa, chocolate syrup, and cheese dips. These dips vary in pH and viscosity (thickness).

As expected, without double-dipping, the foods had no detectable levels of bacteria. After double-dipping, the salsa had five times more bacteria than the chocolate or cheese dips. However, about two hours later the bacterial levels in the salsa dropped to the same levels as the chocolate and cheese.

The researchers explained that salsa has lower viscosity than chocolate or cheese but is more acidic. Since salsa is less thick, more of the dip touching the bitten cracker fell back into the bowl increasing the bacteria level. And the higher acidity killed off most of the bacteria after the two hours.

So, what should we do about all of this? If you’re at a party, please don’t double-dip – especially if you’re sick. If you see someone else double-dipping, avoid their dip of choice. The researchers also provided a useful observation to party hosts: “cheese dip will run out faster than salsa since more of the cheese sticks to the cracker or chip on each dip.” You’ll have to refill the bowl more often but you’ll reduce the chance that people double-dip.

Isn’t science useful?