Is Double-dipping a Food Safety Problem or Just a Nasty Habit?

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

We tested All Natural Tostitos Chunky Hot Salsa (pH 4), Genuine Chocolate Flavor Hershey’s Syrup (pH 5.3) and Fritos Mild Cheddar Flavor Cheese Dip (pH 6.0).

So, how dirty is your dip? We found that in the absence of double-dipping, our 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). But two hours after double-dipping, the salsa bacterial numbers dropped to about the same levels as the chocolate and cheese.

After two hours, levels of bacteria in the salsa were similar to levels in the cheese and chocolate dips.
Paul Dawson, Author provided

We can explain these phenomena using some basic food science. Chocolate and cheese dips are both pretty thick. Salsa isn’t as thick. 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. After two hours, the acidity of the salsa had killed some of the bacteria (most bacteria don’t like acid). So it’s a combination of viscosity and acidity that will determine how much bacteria gets into the dip from double-dipping. 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. And yes, this is something we discovered during the experiment.

Should I freak out about double-dipping?

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