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Methods for preserving/packaging food
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Elizabeth Tracy
(mariposa) - M

Locale: Outside
Methods for preserving/packaging food on 03/30/2010 17:03:05 MDT Print View

Can anyone explain the difference between...

Dehydrated food
Freeze-dried food
Vacuum-packed food
Foil-packed food (such as tuna in a foil packet)

1) What is the purpose of each?

2) How does each method preserve the food?

3) Most importantly (for me): How much of the nutritional value of the food is preserved in the process?


Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Methods for preserving/packaging food on 03/30/2010 17:36:01 MDT Print View

Elizabeth, there are several posters here that specialize in this topic. Let me just start out.

Dehydrated food generally refers to air dehydrated food. That is normally done with a lot of warm air passing over the food bits. Many of us have our own dehydrators at home. They are particularly good at foods that have a lot of natural water in them, like wet fruits. Generally the dried food can be kept in air-tight bags for quite some time. You might need to simmer some of these a lot to get the original texture back.

Freeze-dried food processing is done commercial commerically since it involves vacuum and cold temperatures. It costs more money, but it does a more thorough job of removing water. If the processed food is kept completely air-sealed, it can keep for a very long time. If sealed in foil and plastic, it might be good for at least a couple of years. If sealed in a steel can, it might be good for 10-20 years. Fat does not freeze-dry, so meat must be very lean to go through this. Sometimes backpackers will buy f.d. food and tear open the bulky foil and plastic package just a day before they depart on their trip. They dump the food into a skimpy plastic bag, because that will be good enough for a short period of time. If kept for a long time that way, it would degrade a bit. It probably does not become harmful, but the nutrients and flavor will degrade first. You can probably eat f.d. food for a long time, but you might want to take a daily supplemental vitamin pill. Also, you might want to rehydrate the f.d. food excessively, like simmer it, to make sure you get a more natural texture that your body can digest.

Foil packed food such as tuna is air-tight. Also, it is packed in water or oil, which tends to keep the nutrients, texture, and flavor good, at least somewhat past the expiration date on the package. The only problem is that it is a little heavy or a lot heavy. It is almost as good as fresh food, IMO.

If I were heading out on a long trip now, I would likely have some of each of these types.

Javan Dempsey

Locale: The-Stateless-Society
Re: Re: Methods for preserving/packaging food on 03/30/2010 23:53:10 MDT Print View

You can freeze dry at home using dry ice, a tupper, and a freezer. The results aren't as good for some items, but great for some others.

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Re: Re: Methods for preserving/packaging food on 03/31/2010 00:22:41 MDT Print View

"You can freeze dry at home..."

Please explain.


Laurie Ann March
(Laurie_Ann) - F

Locale: Ontario, Canada
freeze-drying at home on 03/31/2010 09:10:03 MDT Print View

Javan, I'd love to hear more about this too... it would be fun to try out.

Elizabeth... a very high percentage of the nutrition remains with home dehydrated foods provided you store the dried goods out of the light. Most will keep their nutrition for 6 to 8 months with the exception of sweet potatoes. Sweet potatoes start to lose flavor and nutrition after about 3 to 4 months.

Edited by Laurie_Ann on 03/31/2010 09:11:55 MDT.

Javan Dempsey

Locale: The-Stateless-Society
fd at home on 03/31/2010 10:02:49 MDT Print View

Take a tupperware container with a reasonably tight fitting lid, poke a couple holes in the top for gas exchange, a few small holes, nothing big like a loose fitting lid would give.

Depending on the food you're drying and it's water content, you'll need more or less dry ice. I start with about equal ratios and move up from there.. Honestly for most things you can probably start with double, but for flowers/herbs use about 1:1, somethings you need alot more.

Put dry ice on the bottom of the tupper, place item to dry on top of the dry ice.

Place in freezer, check progress 12 hours later, add more dry ice as needed.

Eventually you'll know how much dry ice you need to complete the process.

Also, if you have a freezer in bad shape it may cause issues.

The idea is to have the dry ice in an environment with a near 0 relative humidity. When something is enclosed with the dry ice in these conditions, water molecules migrate to the dry ice, causing the relative humidity of the co2 to increase and the moisture content of the item being dehydrated to decrease.

Now, the temps can cause issues with real watery stuff. I've only used this method 5 or 6 times with varying levels of success. I've heard some people use a cooler in some environments with different things also.

Also, I've had great luck using this with already partially dried items.

YMMV, obviously, this is a hack method.

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: fd at home on 03/31/2010 11:00:53 MDT Print View

I don't see where you introduce the vacuum. Part of the freeze-dry process drops the pressure down to a near-vacuum.

This sounds more like a process for freezer burn.


Javan Dempsey

Locale: The-Stateless-Society
call it what you will on 03/31/2010 21:42:34 MDT Print View

Alot of things are done differently on an industrial scale Bob.

Think what you will, but there's a difference between letting something dry out slowly in the low humidity environment of the freezer and the method I outlined. It's apparent in the taste. Of which I'll note that many industrially freeze dried goods taste like crap.

Either way, technically, just letting it sit in the freezer exposed is freeze drying also.