If you chop up a head of lettuce, what's the best container to put it in?!

I would highly suggest the green bags I think the name brand is Debbie Meyer. You can buy them many places, bed bath beyond, probably your grocery store. I actually recommend them for all your produce. They also make green containers with lids. They really work, obviously it will not last forever but it does last longer.

Either tear it with your hands or buy a plastic lettuce knive (the metal blade will cause the cut edges to turn brown.
You can store it one of two ways, 1) in a container with a damp paper towel (the container has to have airflow) 2) in a containter of with cold water (again has to have air flow)
Lettuce is 80% water, like celery, and will stay crisper when there is water/moisture in the container

Rest owner

Air tight is good but the real enemies are going to be oxidation and moisture.

You can reduce oxidation by using a very sharp knife to cut the lettuce (don't tear it) and putting a paper towel in the container to absorb moisture. Be sure to dry the lettuce well after you wash it.

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don't chop it up tear the lettuce if you chop it. it will start to brown from the oxidation from the metal of the knife. then any container will work fine cut don't cut it.

cooked for 12 year we never cut more than a days worth. even then it was starting to turn brown by the end of the night.

What's convenient for you, airtightness is the big thing. I usually let it go a couple days at the longest, but that's b/c it's eaten by then. And people are divided on cut with a knife v. tear up with hands since edges will darken supposedly for using metal; but it doesn't affect the taste.

Wash it, wrap in a damp paper towel and put it into a Tupperware type of storage.
I also like the Green Bags, no paper towel.
I can't really get it to last much longer than about 4-5 days but I can keep it crisp.

a container that is really protective when sealed, like tupperware can sometimes do the trick and so can ziploc, but i wouldn't guarantee that it would stay fresh for long...

Try those airtight containers (Lock and Lock). It'll stay fresh and crunchy for about three days.