Science: Don’t double dip that chip!

Dip_wPotatoChips_blogIt’s a question that has been pondered by party-goers for centuries and now that we have entered into the season of holiday celebrations and get-togethers, the answer has never been more crucial.

What are the dangers of double-dipping? Can the bacteria in your mouth really make it onto a chip then into the dip? Is this habit simply bad manners, or are you actively contaminating communal snacks with your particular germs? Some have argued that double-dipping is really like putting your whole mouth right in the dip, while others find it hard to believe you could contract an illness from the double-dipper standing next to you at the hors d’oeurves table.

One undergraduate research team at Clemson University set out to set the record straight and designed a series of experiments to find out just what happens when double-dipping occurs. While testing to see if there is bacterial transfer seems straightforward, there are more subtle questions to be answered. These include, how does the acidity of the dip affect bacteria and do different dips affect the outcome?

It all started with a cracker

According to the study, the researchers started their experiment with a cracker and a glass of water to find out if mouth bacteria does indeed transfer and if so, how much? The students started by comparing bitten versus unbitten crackers, measuring how much bacteria could transfer from the cracker to a cup of water. They found that about 1,000 more bacteria per milliliter of water were present when crackers were bitten before dipping, compared to the water in which the unbitten crackers were dipped.

In a second experiment, the students tested bitten and unbitten crackers in water solutions with pH levels typical of food dips (pH levels of 4, 5 and 6, which are all toward the more acidic end of the pH scale). They tested for bacteria right after the bitten and unbitten crackers were dipped, then measured the solutions again two hours later. Unsurprisingly, they found that more acidic solutions tended to lower the bacterial numbers over time.

But what about the dip?

Next, researchers compared three kinds of dip: salsa, chocolate and cheese dips, which happen to differ in pH and thickness (viscosity). Again, they tested bacterial populations in the dips after already-bitten crackers were dipped, and after dipping with unbitten crackers. They also tested the dips two hours after dipping to see how bacterial populations were growing.

What they found was that in the absence of double-dipping, the foods had no detectable bacteria present. Once subjected to double-dipping, the salsa took on about five times more bacteria (1,000 bacteria/mL of dip) from the bitten chip when compared to chocolate and cheese dips (150-200 bacteria/mL of dip). Two hours after double-dipping, however, the salsa bacterial numbers dropped to about the same levels as the chocolate and cheese.

The article explains this happened because chocolate and cheese dips are both fairly thick dips, while salsa is not. The lower viscosity means that more of the dip touching the bitten cracker falls back into the dipping bowl rather than sticking to the cracker. And as it drops back into the communal container, it brings with it bacteria from the mouth of the double-dipper.

Salsa is also more acidic than the other dips, so after two hours, the acidity of the salsa had killed some of the bacteria. The researchers explained that it’s a combination of viscosity and acidity that will determine how much bacteria gets into the dip from double-dipping.

Also, as a side note about party hosting: cheese dip will run out faster than salsa since more of the cheese sticks to the cracker or chip on each dip. That could reduce the chances of people double-dipping.

Is now a good time to start freaking out?

According to this experiment, science has confirmed that bacteria does indeed transfer from the cracker or chip to the dip during double-dipping. However, science has also told us before that many of the germs humans carry are harmless.  Nevertheless, we also know that serious diseases such as the pneumonic plague, tuberculosis, influenza virus, Legionnaires’ disease and severe acute respiratory syndrome (SARS) spread through saliva.

With all this in mind, the article concludes there is some level of concern over the spread of oral bacteria from person to person via double-dipping. A person doesn’t have to be showing symptoms of illness to pass on germs either, so it’s probably best to steer clear of a suspected double-dipper’s favorite snack at a party. And if you were among those who saw no real danger in the act, do your friends a favor and kick the habit once and for all.

For more information, click here.

For Seinfeld’s classic chip double-dipping scene, click here.

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