OldManRiver said:

i have used both a FoodSealer and a chamber vac sealer, (LEM from Costco) and have never noticed fruits getting soft.  I have kept some for easily 6 months, and the fruits are hard as rocks. 

Leaving air in may be the culprit. Was it humid when you packed them?  3 mil is also pretty thin, maybe edges of the fruits poked through? You would have seen the loss of the vacuum if that happened.  I'm using 4 mil bags in the chamber vac with good results.

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OldManRiver said:

i have used both a FoodSealer and a chamber vac sealer, (LEM from Costco) and have never noticed fruits getting soft.  I have kept some for easily 6 months, and the fruits are hard as rocks. 

Leaving air in may be the culprit. Was it humid when you packed them?  3 mil is also pretty thin, maybe edges of the fruits poked through? You would have seen the loss of the vacuum if that happened.  I'm using 4 mil bags in the chamber vac with good results.

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Humidity was probably somewhere in the 40-60% range when I packed. With a small (though not zero) amount of air in the bag I would be surprised if there was enough water in there to effect the change.

Well, we can probably calculate how much water was in there...



OK with worst-case RH for and a typical temp for packing day a month ago, and guessing the air volume in the sealed bag is 50 mL ... which is probably high ... there should be 0.00065 mL of water in the air in the bag. That seems negligible.

@Nonagon did post that he determined his bags gained weight though, so even if the water vapor inside the bag upon sealing is a factor ... Water is getting in, too.

Since I saw a 2 gram bag go soft at 1 month (maybe before, can't say) and a 30 g bag of the same age still seemed OK, I figure the outcome has to do with the amount of dry fruit, the surface area of the bag, and the permeability of the bag. If the small bag went bad then I would expect the bigger bag to go bad eventually.

My 3 mil bags definitely had a good seal, I have used over a thousand of them over the years and know them well. The dry fruit would probably not be strong enough to puncture a 3 mil bag at full squeeze, that takes something like a bone or shrimp shell... And at 75% vacuum, the bags were merely snug.

It's good to hear your 4 mil bags seem to be working. When you have cracked a 6 month bag open... How much fruit was in there? And did you add a desiccant pack?

Benson said:

Wonder how the big boys store weight long term?

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I wondered about that too. In a documentary I saw the inside of a dispensary and it just looked like big plastic jars.

I started testing mylar bags... Hade to figure out the right seal settings. These 100% vacuum tests (dry popcorn) held seal overnight which is a good sigh, but not a guarantee. I guess I will keep a tightly packed test bag alongside any more loosely packed mushroom bags, since the tight pack makes it easy to see if the seal was actually poor. 

ChatGPT said:

You're correct that the molecular size of water molecules is larger than oxygen (O2) or nitrogen (N2) molecules. In a general sense, the permeability of a material to a specific substance is influenced by various factors, including molecular size, structure, chemical interactions, temperature, pressure, and the nature of the material itself.

In typical scenarios, many plastics, including those used for vacuum-sealed bags, have relatively low permeability to gases like oxygen and nitrogen due to their molecular structure and the close packing of polymer chains. However, water vapor molecules, while larger than individual oxygen or nitrogen molecules, can still permeate through plastics more easily than these smaller gas molecules under certain conditions.

Water vapor permeability can be influenced by the molecular structure of the plastic, humidity levels, temperature, and pressure. Over time, especially in conditions where there's a significant difference in water vapor concentration or pressure between the inside and outside of the bag, water vapor can slowly diffuse through the plastic.

Keep in mind that the permeation of water vapor through plastics is typically a slow process and depends on several factors. High-quality vacuum-sealed bags are designed to minimize this permeation and maintain the integrity of the seal for a reasonable duration, providing effective protection against both air and moisture. However, complete impermeability to water vapor is difficult to achieve in practice over extended periods.

For critical applications that require true waterproofing, specialized impermeable materials or containers designed explicitly for such purposes would be more appropriate.

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Kinoko314 said:

Did the mylar bags work okay with a foodsaver, or what did you use?

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NoChill said:

I've been messing around a little with inert gases (argon, nitrogen, etc.) used in wine preservation for displacing the air in my long-term storage jars.

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Tiamo said:

We could probably offset the moisture creeping in by using desiccant and keeping the bag in a dry environment. I am not sure how the WVTR would scale if you kept the bags in 50% RH? I assume it is not linear.

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WeavieWonder said:

I noticed a significant loss in potency after eight months or so from vacuum-sealed mushrooms. Regular food saver bags with no desiccant or oxygen scrubbers. I double bag so the mushrooms don't poke holes.

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Bustaboo said:

Could you weigh a paper towel or napkin, vacuum seal it, and submerge it in water for faster testing of permeability or leaks?

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