The effect of “double-dipping” crackers/chips on the transfer of bacteria from the mouth to the dipping solution was determined in three separate experiments. In experiment 1, eight subjects dipped crackers either three or six times into sterilized water either without biting or biting before each dip. The dipping solutions had higher (P ≤ 0.05) bacterial populations when crackers were bitten before dipping compared with when no double-dipping occurred. The second experiment utilized sterile water dipping solutions with pHs of 4, 5 and 6, and tested the solutions at 0 and 2 h after dipping. There was again significant (P ≤ 0.05) bacterial transfer due to biting then dipping; however, the pH 4 dipping solution had initially lower bacterial populations than the higher pH solutions and even lower populations after 2 h. In the third experiment, three dipping solutions (salsa, chocolate sauce and cheese) were tested, and higher initial populations (P ≤ 0.05) were transferred to the salsa compared with chocolate and cheese; however, the salsa had lower levels of bacteria after 2 h of hold time at room temperature. Three experiments determined that the bacterial population of food dips increased due to the practice of “double-dipping,” and that dip type can influence the dip's bacterial population.


The practical application of these results to food safety will be similar to studies on hand washing. It is clear that foodborne disease can be spread by both practices (double-dipping and improper hand washing), and showing this is true using controlled studies may change the behavior of some people some of the time. But like hand washing, a no double-dip policy will not prevent the practice nor prevent the spread of disease. By determining that the bad practice of double-dipping does in fact transfer oral bacteria to a food dip, the practice may be reduced, subsequently reducing the spread of harmful microorganisms to some degree.