KNOWLEDGE YOU CAN USE

KNOWLEDGE YOU CAN USE
The Five-Second Rule: How clean is that food you just dropped?

In 2007, two students at Connecticut College decided to test the “five-second rule”: the idea that it’s safe to eat food you’ve dropped on the ground as long as you pick it up within 5 seconds. They dropped apple slices and Skittles candies on the floor of the cafeteria and a snack bar, let the foods lie there for 5, 10, 30, or 60 seconds, and then tested them for bacteria.

Question 13.7

Q: Is the five-second rule valid? The students found no bacteria on the food picked up within 30 seconds. After a minute, the apple slices had picked up some bacteria, but the Skittles had none (in a later experiment, they found bacteria on Skittles only after 5 minutes). The students concluded that the five-second rule should get an extension, proposing that you have 30 seconds to pick up moist foods and more than a minute to pick up dry foods without risk of bacterial contamination.

Question 13.8

Q: Should we worry less about bacterial contamination of food? This question is a serious one and warrants more study. Each year in the United States there are more than 76 million cases of illness caused by contaminated food, including more than 5,000 that are fatal.

Question 13.9

Q: Scientific method and drawing conclusions: can you generalize from a small number of observations to all possible situations? In the Connecticut College study, the students examined two food types, dropped in just two locations, and onto surfaces with unknown concentrations of bacteria. In another study, published in the Journal of Applied Microbiology, researchers focused on Salmonella bacteria. Because it has been documented that bacteria can survive on clothes, hands, sponges, cutting boards, and utensils for several days, the researchers decided to drop food on surfaces known to be covered in bacteria.

Question 13.10

Q: Which factor is more important for dropped food: location or duration? Armed with slices of bologna and pieces of bread, the researchers found that when dropped on surfaces covered with Salmonella and left for a full minute, both types of food took up 1,500–80,000 bacteria. And although picking up the food quickly—within just 5 seconds—reduced by 90% the number of bacteria present, 150–8,000 bacteria still had time to hitch a ride on the food in that first 5 seconds. These experiments were replicated, with no significant differences, three times, on separate days.

A grubby conclusion: It’s probably safe to say that if you’re in the Connecticut College cafeteria, you can eat your dropped food as long as you pick it up quickly. But for all other situations, a bit more caution is advised—particularly, taking notice of the “drop zone.” Unsanitary surfaces likely to have microbes will contaminate your food almost immediately. So hold on tight.

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