Anyone tried freeze drying using dry ice?

another_buffalo(6)January 3, 2013

Freeze dried fruits and veggies are so terribly expensive, yet they are more nutritious, taste better and store longer. I've been trying to figure out how to freeze dry my garden and orchard produce. There don't seem to be any 'gadgets' to make this possible.

In searching the web, I found folks using dry ice to flash freeze produce and dry through the process of sublimination. Fortunately, I have been able to enlist the support of a very bright engineer friend to help plan my project. He has come up with some excellent suggestions and I'm looking forward to experimenting.

Just wondering what experiances you folks may have had in trying this?

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wertach zone 7-B SC

That sounds interesting! Let us know what you come up with!

A quick search brought this up:

Here is a link that might be useful: How to prepare Freeze Dried Foods

    Bookmark   January 4, 2013 at 12:24PM
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digdirt2(6b-7a No.Cent. AR HZ8 Sun-35)

I assume you live where you have ready access to dry ice? Nearest supplier to me is over 100 miles away so access, not to mention the cost, would be prohibitive.

Dave

    Bookmark   January 4, 2013 at 12:32PM
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another_buffalo(6)

Hey Neighbor Dave
I'm in Missouri, only a mile from the AR line. I called Harps in Bentonville and they carry dry ice. Some Walmarts even carry it as do some welding supply companies. The trick is to figure out the closest place. I called harps and they said it was $1.10/lb and you just choose the size you want. I have not tried it yet, of course.

I'm actually planning to build my own ice "chest" and then put it in a small chest freezer. My engineer friend says the trick is to keep the dry ice going as long as possible. Don't know when I'll get the ice chest built, but I'm looking forward to doing so. It will be made from 2" mylar backed insulation from Lowes.

    Bookmark   January 4, 2013 at 1:03PM
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another_buffalo(6)

Wartach - Thanks for the link, I had not seen that one. Unfortunately, I don't think it would work the way described. The process of freeze drying requires that the moisture in the food be subliminated out (turning into a vapor from a solid the way dry ice does). If you put the foods into bags BEFORE freezing, the moisture cannot evaporate from the surface.

On the other hand, it says the freezer container must be FULL for the process to work. If this is true, I may need to reduce the size of my ice chest. Hummmmm More research needed. Thanks for the input.
Carol

    Bookmark   January 4, 2013 at 1:14PM
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wertach zone 7-B SC

"If you put the foods into bags BEFORE freezing, the moisture cannot evaporate from the surface."

I was thinking the same thing! The bags will hold the moisture in. IMHO I believe that the food should be mostly exposed. Maybe have it between layers of foil, cloth, parchment paper, or something else, not sealed, so that the moisture could evaporate? Then bag it.

Also as Dave said the cost is another consideration. I can buy a 5lb. bag of dry ice at my local Publix for $6. I have a really good ice chest that I have used for storing dry ice before, for a Halloween party. After layering I probably would only end up with about enough to fill about 8 quarts of freezer bags. Just a guess.

If you don't count labor, it would be a little cheaper than store bought.And You would know what was actually in the bags!

    Bookmark   January 4, 2013 at 1:52PM
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backyardbum

be extreamly careful with the dry ice. It can cause severe burns in seconds.

    Bookmark   January 6, 2013 at 12:24AM
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another_buffalo(6)

You are right, backyard. And it replaces oxygen in a room, so that needs to be kept in mind in closed places. As far as expense goes, if you check out the price of the freeze dried foods, it is a whole lot more than $1/qt - more like $20 or more. If you purchase the food and buy ice, that would bring the cost closer. But I'm looking for the BEST way to store my own home grown stuff.

I could not wait until I made my own ice chest, so started my first experiment last night. I stopped by Lowes and found a plastic light grill that was in about quarter inch spacing. It cut easy into sections with the band saw to form shelves. I have sliced apple, banana, pineapple, nectarine and ice cream on shelves in a stryofoam shipping container in the chest freezer.

I put a good sized piece of dry ice on the top shelf and the rest on the bottom. The plan is to not check on it for three days. Then open the top and see if the large chunk of dry ice is gone. If it is, I'll test the products to see how they faired. Looking forward to a party a week from today where I can report on the results. Who know, maybe I can even 'bring the ice cream', dried that is.

    Bookmark   January 6, 2013 at 11:08AM
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wertach zone 7-B SC

Let us know how it turns out!

    Bookmark   January 6, 2013 at 1:17PM
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another_buffalo(6)

First report back. The test was all but a disaster. Apparently I did not have the lid down good on the cooler in the freezer. There is a lot of ice on the side of the freezer where the gap was - and even on the other sides of the freezer. It had not been but two days but I opened the cooler anyway. The dry ice was gone. The food was not 'dry', but the apples were 'carbonated' - and interesting taste. I had used 7 pounds ($8) of dry ice for the experiment.

I'm not giving up - but its not looking good. THe food is still in the freezer. This afternoon when I go to town, I will pick up some more dry ice and take the cooler out of the freezer this time. Definately not cost effective at this point, even is it should work. But I really want to see if it is possible without a vacuum.

There is an excellent preview of at home freeze drying at the link below. On a previous page the website has the dry ice method and the home freezer method of dry freezing. I was ready to try the home vacuum method when my engineer friend warned me about implosions. Not sure I was ready to be that brave, I decided to try the dry ice first. In the vacuum method, you freeze dry with dry ice first and just use the vacuum in the drying part of the process.

OK, why you ask am I so interested? Dehydrated foods lose some of their nutritional quality in the dehydrating process (probably about 20%). They continue to decline over time, with a shelf life of around 2 years for eating quality. Freezers will damage products due to large ice crystals and will deteriorate in the freezer over time - and you risk freezer failure. Canning is probably a little longer lived product, but the cooking process definately changes the nutrition and taste of the foods.

That leaves freeze dry. It produces a dry food with 99% of its nutrition in tact and with proper storage conditions (air tight in vacuum sealed jars for example) can last for 30 years in excellent condition. It is restored to almost fresh when rehydrated. A lot of restaurant salad bars use freeze dryed fruits and the public does not even realize it. It is just the ideal way to preserve foods. I would love to be able to do that at home. I'm on a quest for a solution. Unfortunately, I'm becoming resigned to the truth that it may not be possible.........

Here is a link that might be useful: build your own vacuum chamber

    Bookmark   January 7, 2013 at 12:34PM
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wertach zone 7-B SC

I don't know why you are worried about implosions? Explosions, Yes, implosions, not such a big deal! LOL

The vacuum pump in the link that you posted appears to be the same type used for vacuuming auto air conditioners. They are very inexpensive, about $15. I have one.

Keep us updated!

    Bookmark   January 7, 2013 at 1:53PM
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rdback(Z6 VA)

Hi Carol,

Yeah, I was thinking about explosion as well.

I like your idea, but please be careful!

Rick

Here is a link that might be useful: Dry Ice info

    Bookmark   January 10, 2013 at 12:38PM
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another_buffalo(6)

This is a final follow-up to my experiment freeze drying with dry ice. I rate it a dismal failure. It may be theoretically possible to freeze dry foods with dry ice, but it certainly is neither convenient nor cost effective.

Another way of freeze drying in the link above was to flash freeze with dry ice, then put the frozen foods on an open tray in a frost free freezer. I did that with a tray of apple slices. They are not yet at the dehydrated bendable stage after six days in the freezer. I don't know if they will ever get to a dry enough state to snap when bent. I do not rate this system as practical either, because it takes the purchase of dry ice and use of lots of freezer space for the process.

The third method of freeze drying was to flash freeze with the dry ice, then put it in a vacuum chamber to draw out the moisture. Wartach astutely noticed the $15 harbor freight vacuum pump. The acrylic for the top is available from Lowes. I was planning to use a large stock pot for a chamber and a cut rubber mat for the gasket. I would still have to figure out the line to the chamber from the pump. Thanks, Rick for the reminder to be careful with dry ice.

At the moment, I am so disappointed in the dry ice, I may not even proceed with the vacuum chamber experiment. Its interesting that people put processes on line that they have never tried and then do not report any results of their own experiences. I don't want to leave people with a false impression so am supplying this report.

On a pleasant note, I just finished reading the biography BIRDSEYE, The Adventure of a Curious Man and I highly recommend it. Birdseye learned about flash freezing while living in Labrador and preserving food for the winter. He wondered why foods frozen in mid winter stored so much better than foods frozen in fall or spring. When he returned to the states, he used EXISTING knowledge and technology to invent a practical way to flash freeze foods and store it. Unfortunately he was ahead of his times. There was not distribution or storage available either commercially or in homes to appreciate what he had done. Never the less, food storage world round has been transformed by his success and perseverance. After succeeding in that venture, he turned to dehydration as the most practical way to preserve and distribute foods. He did not live long enough to discover that his original flash freezing was also the key to quality dehydration.
Carol

    Bookmark   January 12, 2013 at 10:20AM
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