Double-Dipping Does Transfer Bacteria: George Was Wrong! (PDF; 232 KB)
Source: Clemson University, Department of Food Science & Human Nutrition

To analyze the true effect of double-dipping, Clemson University’s Dr. Paul Dawson and his Creative Inquiry Team (Testing Variables of Foods, Films, Antimicrobials and Surfaces Affecting Transfer and/or Survival of Bacteria) conducted an experiment with the purpose of determining the extent of bacteria transfer that occurs when someone double-dips. The inspiration of the experiment was a popular television episode of Seinfeld, written by Peter Mehlman, in which the character George Costanza is scolded for double-dipping. First, mouth rinses were performed to measure the average bacteria count present in the mouth under normal conditions. Oral bacterial counts ranged from 5.8×105—4.8×106 CFU/mL (5.8—6.7 logCFU/mL) and averaged 1.8×106 CFU/mL. Second, a series of trials were completed that involved biting a chip and then dipping it in sterile water to determine how much bacteria was transferred from the mouth to the chip and then to the dip. Trials included varying amounts of double-dips and a range of dilutions. In order to observe simply the amount of bacteria transfer, sterile water was chosen as the “dip” and low sodium crackers as the “chips” so that the amount of bacteria in the plates would not be influenced by any factors other than the actual transfer from mouth to chip to dip.

According to the data, a significant amount of bacteria transfer occurred that was attributable to double dipping. Bacterial counts averaged 2.6×103 CFU/mL (3.4 log CFU/mL) for six dips and 1.9×103 CFU/mL (3.3 logCFU/mL) for three dips. It appears that double-dipping does, in fact, contaminate the dip. Whether the amount of contamination is dangerous to the dippers’ health or not is still debatable and can depend on multiple external factors including the type of chip/dip or the relative health/illness of the person whose mouth provided the bacteria. Next time you take a bite of your chip, however, and are tempted to commit a second dip, keep in mind that the numbers have been calculated, and the bacteria are having just as much of a party as you are.

See also: Dips Contaminated by Bite Dipping (PDF; 152 KB)

See: Dip One or Dip Twice (New York Times)

This entry was posted on Wednesday, January 30th, 2008 at 12:37 pm and is filed under Food and agriculture, Health and healthcare, Safety. You can follow any responses to this entry through the RSS 2.0 feed. Responses are currently closed, but you can trackback from your own site.