Why does lettuce stored in a bag stay fresh longer?

Many foods you'll find at the grocery store -- like lettuce, for example -- are stored in special plastic packaging called MAP that helps them stay fresh longer. Find out what MAP is, and how it keeps food fresh longer, in this episode of BrainStuff.

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Episode Transcript

Speaker 1 (00:00):
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

(00:23):
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

(00:47):
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

(01:09):
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,

(01:32):
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

(01:56):
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

(02:18):
com home page.