Professor Donald Schaffner, a food microbiologist at Rutgers University, New Jersey debunked the five second rule for food on floor in a study. The two-year study concluded that regardless of how fast the food is picked up from the floor, it will pick up bacteria with it.
The study tested four different surfaces – stainless steel, ceramic tile, wood and carpet and four different foods – cut watermelon, bread, buttered bread and strawberry gummy candy. The four surfaces were treated with a bacterium similar to salmonella and food was dropped on it from a height of five inches. Next, four different contact times of food with the surface were measured – less than one and five seconds, 30 and 300 seconds. Different combinations of surface, food and seconds were replicated 20 times for a total of 128 combinations resulting in 2,560 measurements.
The study found that no fallen food escaped contamination entirely and that longer contact times resulted in more bacteria contamination. While the transfer rate of bacteria for wood varied, carpet had the lowest transmission rate in comparison to tile and stainless steel. Regarding the food, composition of the food, surface it falls on and the length of time determines the rate of contamination. Contamination was highest for watermelon (with moisture) and lowest for gummy candy.
Experimental Psychologist and professor, William Hallman, at Department of Human Ecology at Rutgers University explained why people still follow the five second rule stating that people make quick decisions with the data available to them. It is a lot easier to pick up and eat a yellow M&M from the floor because germs are invisible thus easier to ignore. Professor Hallman also noted that men are more likely than women to pick up food from floor and consume it. The findings were a result of a phone survey of 1,000 Americans in 2005.
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Christopher Mele, Five-Second Rule for Food on Floor is Untrue, Study Finds, N.Y. Times (September 19, 2016), http://www.nytimes.com/2016/09/20/science/five-second-rule.html.