Plastic that breathes

[Fat Guy]

So I was in the store a while back complaining to the bread-counter guy that they put their bread in plastic bags instead of paper, and he said "But this kind of plastic breathes." Fast forward a few months and I saw some spinach packed in plastic packaging that claimed to breathe. It's not that I don't believe it, but is it true? Have plastics evolved to the point of true breathability? How does that work? Very small holes, I guess.

[Richard Kilgore]

Yes! Russ Parsons has a great chapter on this in his last book, How To Pick A Peach.

[Lisa Shock]

The type of plastic used in regular sandwich bags, cling film, and trash bags is permeable to most gasses. They add multiple layers for the freezer bags, but gasses still travel through it.

http://www.keepsafe.ca/barriers.htm

[scubadoo97]

Yes as one that is doomed to buy bread from the grocery store or make your own I can attest to the fact that loaves of french bread in the breathable plastic bags will turn rock hard if not eaten in a couple of days.

[Chris Amirault]

As a dog owner who recycles bags on walks -- ahem -- I can testify to the fact that produce bags are a poor choice if you're seeking to trap odors. Grocery bags and industrial-baker bread bags are basically impermeable.

[Lisa Shock]

Yeah, I discovered that sandwich bags are permeable when my vet asked me to bring a litterbox sample in with my cat for her exam. I wore gloves while using a clean scooper then washed very well after double-bagging the sample in name-brand zippered sandwich bags. And, my car was filled with litterbox odor anyway.

I later asked someone about it, and they said it was a matter of cost, but it also ensured that people didn't accidentally create botulism-friendly environments in their fridge or kids' lunchboxes.

[paulraphael]

The bread bags at whole foods are plastic, perforated with hiundreds of pinholes. The low tech solution.

Scubadoo, I don't think there's any way besides freezing to keep lean French bread from drying out in a couple of days. I've never seen an unfrozen baguette last even 12 hours.

[Dianabanana]

I have found that any kind of bread, not just lean bread, goes stale in no time in those perforated bags. Much, much prefer a paper bag.

[paulraphael]

I have found that any kind of bread, not just lean bread, goes stale in no time in those perforated bags. Much, much prefer a paper bag.

←

Sourdough boules last several days. I haven't done a side by side comparison with paper, but from casual observation they seem similar to me. I prefer paper for the ease of recyling.

[tirgoddess]

Ziploc makes a bag specifically for vegetables which extends the life of them. The bag is perforated with pinholes. I have to order them out of Canada because they didn't catch on in the US. For all of the produce that I purchase and grow it is worth the extra trouble to have them. I reuse the bags about 5 times so I am getting my money's worth.

[mgaretz]

A standard zip lock style bag (even a "freezer" version) is made out of polyethylene and as others have mentioned, is gas permeable. (The freezer versions are just thicker.)

Polyester (aka Mylar) is, for our purposes, impermeable. It is used to make vacuum sealer bags (at least for the better sealers). However, polyester does not lend itself to heat sealing. So the typical vacuum sealer bag is actually a layer of polyester on the outside and ployethylene on the inside.

[Katie Meadow]

What you keep your bread in sort of depends on what qualities you are trying to maintain, no? If I buy a fresh loaf of Italian bread or a baguette in the morning I might want some for lunch, and keep the rest for dinner. In six or eight hours the bread itself doesn't really get too stale (yes, maybe a little), and keeping it out on the counter seems no different than keeping it in a paper bag. But if kept in a plastic bag, the crust will get dull and soft in less than no time. Does the "breathable" plastic bag keep the crust crunchy for several hours? A non-breathable one won't.

If I keep bread overnight I expect that it will mostly be used for toast, so I don't care so much about the crust. But if left on the counter or in paper overnight, the entire loaf will be dry and stale and even make pretty lousy toast. Overnight bread seems to do best in a non-permeable bag around here. I also assume that humidity and locale must make so difference. The air is pretty dry here in the summer.