The ‘Five Second Rule’ is a rule that many people grew up following. It is the idea that if one drops food on the ground it is still safe to eat if it is picked up within five seconds of dropping it because there would not have been enough time for bacteria to transfer on to the food. Researchers at Rutgers have investigated the validity of this rule.
The researchers investigated the Five Second Rule by using four types of food (watermelon, bread, bread and butter, and gummy candy) dropped on four different surfaces (stainless steel, tile, wood, and carpet). According to the study, they used the bacteria Enterobacter aerogenes.It does not cause disease but is closely related to Salmonella. The study also varied the amount of time that the food was dropped on the surface. The varied times were one second, five seconds, 30 seconds, and 300 seconds.
Donald Schaffner, the conductor of the experiment, cites moisture as one of the factors that most affected the transfer of bacteria from the different surfaces on to the different foods. This is seen in watermelon, which had the highest amount of bacteria transfer, and gummy candy, which had the lowest amount of bacteria transfer. Why is this? Bacteria move with the help of flagella or pilli. Flagella is a long tail structure that moves around to propel the bacteria and pilli cover the bacteria and pull the bacteria forward. The presence of moisture aids the movement of bacteria. Another factor was the length of contact, the longer the food was left on the surface the more contaminated it was with bacteria. The surface that the food ‘fell’ on in the experiment was another factor that affected amount of bacteria. According to Schaffner, carpet had a lower amount of bacteria transferred then tile and stainless steel, and wood varied.
The results of this study are based off of 20 trials of 128 scenarios. In class, we learned that not all data is equal. Data has a stronger inference when it is a properly designed experiment and has an even stronger inference when it is a good experiment with good field observation or evidence of mechanism. This experiment has strong inference because there are multiple trials. Since there are multiple trials, if they all yield similar results this proves the validity of the outcomes. This experiment had 20 trials making the results of the experiment valid as it was a fairly designed experiment. The repeat of trials helps reduce random chance, although it is always still a factor.
I know that I drop food all of the time and then debate whether it is safe to eat or not. This article proves that depending on the food or surface your food may be safe to eat if it is picked up in a short amount of time. However, if your food has moisture and has fallen on carpet or stainless steel- it is safer to not eat the food. If it is a gummy candy falling on a carpet- it is pretty safe to eat. However, this experiment makes me think about the number of bacteria that can be on your food when you drop it. Five second rule or not- its always better to be safe than sorry with food poisoning.
For more information on how bacteria move click here.