Welcome to Brainstuff from house stuff works dot com where smart happens. Hi. I'm Marshall Brain with today's question, how is it that lettuce stored in plastic bags at the grocery store can stay fresh for so long? Many of the foods that you buy wrapped in plastic today are using what's called modified atmosphere packaging or MAP. The package is filled with a mix of gases that are beneficial to the food. Most foods do better if they're stored
away from oxygen. Also, many microorganisms have a hard time with high concentrations of c O two, so eliminating oxygen and adding c O two is very common in modified atmosphere packaging. The amount of time that MAP can add to shelf life can be amazing. The shelf life of meat can go from three to twenty one days, cheese from seven to a hundred and eighty days, and fresh pasta from three to sixty days. That's not bad when you consider that the cost of adding the gas is
practically nothing. Shelf life extension often lowers the cost of a product by reducing spoilage, and also opens up long distance import export options. It can also extend the seasons of certain fruits and vegetables. In the case of lettuce in a bag, the modified atmosphere does two things. First, it changes the way that the green leaves behave The green leaves are still alive even after you pick the lettuce, and you want to keep them alive as long as
possible by changing their behavior. Second, it discourages bacteria. The high c O two and low oxygen atmospheres can lead the less discoloration, slower rotting action for the bacteria, and it helps the lettuce stay crisp longer. Plus there are no added chemicals. Do you have any ideas or suggestions for this podcast? If so, please send me an email
at podcast at how stuff works dot com. For more on this and thousands of other topics, go to how stuff works dot com and be sure to check out the brain stuff blog on the how stuff works dot com home page.