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

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

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.

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

"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!

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

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.

Let us know how it turns out!

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

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!

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

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

Was just wondering if dehydration of fruits and vegetables in a food dehydrator and then using dry ice method to complete the process would be better?? Just an idea that ran thru my head.

Very interesting. Hugh, are you going to try your idea? It would be really nice if it would work safely and economically.

Madonna

Hi all. I successfully used dry ice to dehydrate the Items. I used the cooler outdoor for this. O let it got rock hard before removing from the dry ice and used paper towels to remove any leftover liquid. Now they are finishing off evaporating au naturale

I saw something online that said to put the food in a single layer inside a freezer bag. But leave the freezer bag open, then lay Styrofoam ice chest and put a layer of dry on top. And leave it for a minimum of 24 hours I have not tried it yet, but that is what my search has come up with.

First a little basic science -- from online sources: "At pressures less than 0.00604 atm, therefore, ice does not melt to a liquid as the temperature increases; the solid sublimes directly to water vapor. Sublimation of water at low temperature and pressure can be used to “freeze-dry” foods and beverages. The food or beverage is first cooled to subzero temperatures and placed in a container in which the pressure is maintained below 0.00604 atm. Then, as the temperature is increased, the water sublimes, leaving the dehydrated food (such as that used by backpackers or astronauts) or the powdered beverage (as with freeze-dried coffee)."

The partial pressure of water vapor in the atmosphere is about 4.3 mm Hg at the freezing point. To evaporate, it has to barely exceed the atmospheric pressure of 760mm Hg. To do this, either reduce the pressure, or increase the temperature....or add other substances that can evaporate and contribute the rest of the pressure needed. This is where dry ice comes in. It will sublimate (i.e. -- go from solid to gas without first becoming liquid) at -78.5 C. A stream of CO2 flowing over a fixed source of ice will allow the water to sublimate. The key is to have the CO2 "flow." This is where a vacuum with discharge to atmosphere comes in, or a "sink" for the water, such as a dessicant. Clearly, a small blower will not come anywhere close to procucing a suitable low-pressure: It needs to be a pretty good vacuum. Even then, if the source of the CO2 is dry ice, you will need an awful lot of it. You can see why. Divide 760 mm Hg (total pressure) by 4.3 mm Hg and get the ratio 177:1. So if you have 0.1 lb-mole of water in the food (1.8 lb), you need 17,7 lb-mole of dry ice (779 lb).

Alternatively, if you have a frost-free refrigerator, you can freeze the food and let the refrigerator do the rest. It will sweep atmospheric air over the food, drawing moisture from it in equilibrium with what is in the air. After a few MONTHS the water in the food will likely all sublime. If you have ever put a tray of water in the freezer, and left it, you would come back to find the tray empty, or mostly so. You can spend your money on freeze-dried foods made by someone else, you can run the refrigerator for months and pay the electric bill, you can buy dry ice and a decent vacuum pump (with other equipment), or you can do air drying or home canning. For emergency foods with long shelf-life and break-resistant containers, commercial freeze-dried foods are the way to go. For everything else, home canning and air drying is cost-effective and pretty healthful. As to the vitamins lost in processig, take supplements separately.

By the way, these home vacuum sealers? Yes, they remove oxygen in the air that can otherwise react with food causing flavor and nutrient changes. They don't appreciably change the amount of water so if there are spoilage organisms (there usually are!) that can survive low temperatures in the absence of oxygen (anarobic bacteria), they will continue to grow. One "trick" I've taught is to take steel wool -- maybe a cigarette-sized twist -- and wrap it in a coffee filter. Put it in with the mostly dry food to be preserved, in a very tightly sealed container. The steel wool will react with the water and oxygen inside the container forming rust. The filter paper contains the rust particles so it doesn't mix with the food. As the water and oxygen react, the inside pressure drops. You can see this in a flexible container as it appears "squished." CO2 will not be removed, nor will nitogen or other fixed gases. Since all organisms appear to need SOME water, and that has been converted to hydrated iron oxide, this shouldn't be a problem