Perhaps this is something for the children’s channel, but why is food preserved if protected by a plastic bag? I mean, it isn’t vacuum or anything in that bag, it’s about the same… air…? as outside the bag.
Right?
So… why does it work (for dummies)?
Well, it keeps flies and other insects away from the food…
I think it’s because it keeps out germs.
It reminds me of the experiment (sorry for the gross-out) on meat and maggots. The scientist had thought that maggots came from meat. However, one night he accidentally left one of his meats covered, and found it had produced no maggots. This was a ‘‘lightbulb’’ moment for all concerned.
If you cover your food, germs won’t get in. Bacteria cannot spontaneously produce itself. So if you keep your food in a plastic baggie, it protects (to an extent) outside spoilage-producing agents (such as maggots and bacteria) from getting to the food.
In addition to keeping food cleaner, it also keeps it from drying out.
I think they also help by keeping more oxygen from getting to the food. Assuming the bag is airtight, then there’s only a small amount of air trapped in it (even less so if you “poof” the bag to get most of the air out), and once the oxygen in that air has all reacted with the food, there won’t be any more oxygen to continue oxidizing the food.
Presumably this also helps keep a lid on bacterial and mold growth.
Oh, and I believe it keeps the food from drying out, too.
All good things, unless I’m vastly mistaken. I almost always put my plastic-bag-sealed food into the refrigerator as well, which obviously cools the food down and helps retard bacterial growth and whatnot.
Right. You want the least permeable barrier possible around your food. Plastic is less permeable than paper. Vacuum sealing is the latest high tech fad in food storage, but that’s obviously worthless unless the barrier is unbreachable.
Does food in a plastic bag stay fresh longer?
Usually. Oranges and potatoes don’t like it, but your casserole sure does.
If I put food in a reasonably airtight plastic bag before I put it in the refrigerator, it stays fresh and edible significantly longer than if I just stuff the plate into the fridge by itself – if I don’t put it in a bag, food tends to dry out and get pretty gross within a day or two. Cheese, for instance, gets all hard and icky (and darkens in color, at least for cheddar) within 24 hours or so unless I very carefully seal it up and poof out most of the air. Bread too.
Plus the plastic bag keeps the food inside from absorbing refrigerator odors, which is a definite plus. Particularly with cheese.
ETA: Like my illustrious colleague dangermom points out, it doesn’t work out for all foods. When I put a head of romaine lettuce (er, a heart of romaine lettuce, I think it’s called?) in an airtight ziplock bag the other day, it turned into a big bag of mush. I guess there’s a reason the plastic bags of lettuce from the grocery store are covered with holes.
Yeah, I think it has to do with moisture. Foods that don’t like to be damp shouldn’t be sealed in plastic because they need some air. Lettuce, mushrooms, and so on get too wet and go bad. But most things will dry out and get gross if you don’t wrap them.
here is an odd thing… i’ve notice my salad stuff stays better and crisper in water. i’ll put the lettuce or carrots into a tupperware ™ container, fill it with water, close it up, and pop it in the fridge. when i want to eat them i just drain out the water, take what i want and add more water until i use it all up. it takes me about a week to eat it all.
the lettuce and carrots are very crispy and happy. i even take it into work in my nifty lunch bag still in water and put it into the fridge there.
Huh. I do that for celery and carrots but it never once occurred to me to try it with lettuce. I don’t like wet lettuce but I may have to try that especially if it slows the process of the leaves turning pink.
I’ve also heard moisture is a factor in food texture/flavor changes. If a food is normally dry, it tends to suck up water in the fridge/freezer, and if it is normally wet it will do the opposite. Both paths result in food staleness. Perhaps the plastic bag helps either from happening.
edit: this was the explanation I heard for why french fries are terrible when left in the fridge (they absorb moisture) but pizza is still excellent (the cheese prevents the moisture of the sauce from reaching the bread).
This is how it’s done in restaurants (at least the one’s I’ve worked in). The chef (or more likely an underling) washes and cuts up the lettuce, and then puts it in a bucket of water in the refrigerator. When a customer orders a salad, the chef grabs a handful of lettuce from the bucket, dries it in a spin dryer, and uses it to make the salad.
You know the saying “One bad apple spoils the barrel”, right? It’s true. If you have a piece of rotting fruit in proximity to other fruit, it will speed the ripening/rotting of the other fruit. Ripe or damaged fruit releases ethylene, which promotes ripening in other fruit. You can hasten the ripening of fruit by storing it with fully ripe fruit (bananas and apples both release a lot of ethylene) or by enclosing it in a bag to trap the ethylene with the fruit.
When fruit ripens, starch is converted into sugar. You can stain cut fruit with iodine to check its ripeness. Iodine binds to starch, so unripe fruit that is painted with iodine will be dark, while ripe fruit, which has less starch, will be unstained. It’s fun and easy to test this for yourself.
Maggots are fly larvae. They feed on spoiling meat but do not cause spoilage. They develop from eggs laid in the meat by flies. Maggots have been used therapeutically to treat skin disease by removing necrotic tissue. Spoilage, OTOH, is caused by bacterial activity. Most bacteria that cause spoilage are already in the meat; the bacterial activity is retarded by refrigeration. Beef is “aged” before you buy it, which just means it is allowed to spoil a little bit under controlled conditions. Aging actually improved the flavor, though I don’t know exactly why; it reduces gaminess.
Mold spores are common in the air and can cause moldiness (which is not exactly the same as spoilage but might as well be for all practical purposes) if food is exposed to open air.
That isn’t what aging means. When meat has spoiled, it is inedible. The purpose of aging is to allow the meat’s own enzymes to digest the tougher connective tissue to make it more tender. The conditions are controlled to retard spoilage - low humidity and low temperature.
An example of a foodstuff that is allowed to “spoil a little bit” would be something fermented or cultured, like cheese, yogurt, beer, wine, etc.
Purpose of plastic bags or vessels:
1: Prevent drying
2: Prevent oxidation
3: Serve as a barrier to vermin or ambient microbes
4: Prevent the unwanted migration of flavors or odors
5: Prevent the food from soiling the refrigerator or cabinet (obviously)