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Or "does bread benefit from being in a sealed bag once frozen?"

I bake bread rolls regularly and freeze them in sealed plastic bags, and then I thaw one or two at a time. Sometimes I don't bother resealing the bag afterwards, which leads me to this question. I've been assuming that sealed bags help during the freezing process, but does it matter once they're already frozen?

I'm mainly focused on moisture and water content, and I'm excluding the fact that it'll adsorb taste from e.g. onion fumes.

I've been assuming that all water is locked up as ice, but after trying to freeze soy sauce and ending up with a brown freezer I know from experience that I don't always catch the important details.

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    A chest freezer that gets very cold (mine goes to -17 °F) and doesn't have an auto-defrost feature will help with this.
    – aswine
    Commented Apr 24 at 15:31

2 Answers 2

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Freezers are extremely dry, over time without protection food will develop 'freezer-burn', where the outside of food dehydrates and loses quality. A sealed bag will make a big difference in preserving the quality of food in the freezer.

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    Though in a typical freezer (especially a self-defrosting aka automatic defrosting one, where the temperature varies quite a bit) plenty of water will slowly migrate from the contents to form frost on the interior of the bag, leaving a drier product, as well. That's one reason to avoid excessively long freezer storage. It's also a reason to minimize airspace in the bag, but vacuum-packaging bread has other downsides, so don't go there.
    – Ecnerwal
    Commented Apr 23 at 17:38
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    @Ecnerwal type of seal makes a big difference in this. Vacuum-packed items get less freezer burn because there's nowhere for their moisture to migrate to, unlike looser-packed items.
    – FuzzyChef
    Commented Apr 23 at 17:40
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    "Here's a rather dense breadstick. It was a baguette before I vacuum-sealed it" ... ;^)
    – Ecnerwal
    Commented Apr 23 at 17:42
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    @Ecnerwal : Maybe freeze it, then vacuum seal it so can’t squish down?
    – Joe
    Commented Apr 24 at 0:59
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    @Ecnerwal most vacuum sealing machines allow for an early triggering of the sealing part, thereby applying little pressure/vacuum to the food while still removing most of the air. This is very close to just carefully flattening a regular ziploc bag with a good seal
    – Hobbamok
    Commented Apr 24 at 13:46
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I've been assuming that all water is locked up as ice

At the temperatures in a home freezer, that's not quite true. Solid ice still has a vapor pressure as some of the water is able to escape. Given some time (usually weeks), the moisture content in the product can drop enough to affect the the food.

Colder temperatures reduce the rate this happens, but you probably don't have more than a few degrees that you can adjust a home freezer.

Removing any space for the sublimated water to go (sealing) can help some foods. But most breads have lots of empty spaces in the interior. Even if water can't leave the roll, it can leave the bread matrix and form ice crystals in the voids. When the bread is warmed, those ice crystals will melt and form drops of water. Wrapping will help a bit, but won't stop that process.

  • Yes the sealed bag helps even after fully frozen by reducing the rate of moisture loss.
  • Expect that a perfectly sealed bread roll will still suffer from loss of texture after an extended period in your freezer (probably more like weeks rather than months, but that depends on the product, the freezer, how often the freezer is used, and your tastes).
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  • "At the temperatures in a home freezer, [...] Solid ice still has a vapor pressure as some of the water is able to escape." - Out of curiosity, what temperature would be needed to reduce the vapor pressure enough that in a practical sense foods wouldn't dry out?
    – marcelm
    Commented Apr 24 at 18:51
  • I don't have any personal info (I'm sure industrial frozen food companies would know more), but pressure drops slowly with temp: lyotechnology.com/vapor-pressure-of-ice.php has a chart. Laboratory freezers that go to -80C are widely available.
    – BowlOfRed
    Commented Apr 24 at 19:31
  • Yeah, -70°C is (or perhaps was, if the available tech has improved to make lower practical) a very typical temperature for lab sample storage.
    – Ecnerwal
    Commented Apr 24 at 20:21
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    I've noticed that ice cubes left in the freezer for weeks or months will slowly shrink due to this effect.
    – Michael Seifert
    Commented Apr 25 at 11:54
  • I know this sandwich doesn't exist. I know that when I put it in my mouth, the Bread Matrix is telling my brain that it is juicy and delicious. Anyway... I interpret your answer as that the effect is likely negligible if consumed within two weeks, but should be kept in mind otherwise.
    – Andreas
    Commented May 11 at 22:44

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