Freeze drying food

[retired profile of WrethaOffGrid]

Hmmm, caverdude, I’m thinking liquid nitrogen for quick freezing…

Wretha

[Anonymous]

I have been freeze drying food for about 4 months now. I’m using a normal deep freeze for freezing the sample. I have a flexi-dry lab freeze dryer to use as a cold sink to trap the moisture. I use a rotary vane vacuum pump.

The process is very simple if you are freezing items that you would normally freeze, (ie items that don’t break down from large ice crystal formation)like hamburger, fried potatoes, pork, beef, chicken, etc. Basically you freeze the item, then apply a vaccum less than 6 mbar and let the food come to room temperature or the temperature of your heat source. I use 8 incandescent 100 watt bulbs as a heat source.

I use mason quart jars as my vacuum dry vessels. I dry 6 jars at a time and they normally take 24 hours, depending on the consistency of the food item.

It is a great system for saving left-overs.

If you want to dry high sugar items like fruits or you want to retain the structure of high moisture items like green peppers you will need a colder freeze, at least -30 degrees C.

[caverdude]

Well food saver has an attachment for pulling vacuum on canning jars. But I don’t follow exactly how you are using the jars? wouldn’t you have to remove the moisture by continuing to vacuum as the moisture leaves the item being freeze dried.

It is interesting that you are achieving some good effects at lower temperatures with some food items. Do you have a link for the a sales site of your vacuum pump?

https://blog.larrydgray.net

[Anonymous]

https://www.ebay.com/itm/FTS-Systems-FDx-1-84A-CD-Flexi-Dry-with-Pump-/380410459800?pt=LH_DefaultDomain_0&hash=item58923af698

This is close to what I am using. To use the jars I drilled a hole in the normal flat and used plastic sprayer fittings. The fittings are L-shaped with a normal 1/2″ hose barb on one side and thread and nut on the other. I used some rubber washers and screwed the nut tight. Then just screw the lids on using normal rings until hand tight. The vacuum then pulls out through the fitting into 1/2″ plastic tubing secured with hose clamps. The other side of the tubing fits the tubes coming out of the manifold on the Flexidry.

You do have to keep the vacuum running the entire time. You can tell the food is dry when you can no longer feel any cold in the food when you pull it out. Sometimes I have to leave it in the jar for a second cycle. Especially very wet, dense foot like tuna.

I don’t know if this is the site where I bought the pump, but this is the pump I have: https://www.ebay.com/itm/Robinair-15600-6-CFM-2-Stage-Vacuum-Pump-/380384455905?pt=LH_DefaultDomain_0&hash=item5890ae2ce1

[caverdude]

Thanks, this is sounding like something I may want to try myself sometime..

Can you list food items that you feel freeze dry very well this way and others that you feel won’t because of ice crystal formations? Or maybe its a matter of size of the pieces of food too, for example if a food item was finely chopped, it might be ok using this method, but if you want it to remain similar in properties at larger size pieces then the fast deep freeze would work. On another note, what if a person used dry ice for quick freeze, and how much might that cost. Or liquid nitrogen. I mean are there lower cost methods for quick and deep freeze at least on a smaller scale production.

https://blog.larrydgray.net

[Anonymous]

I’ve found this is all an experiment. I’ve dried alot of scrambled eggs because we have chickens. I don’t know if they will be very good. I haven’t tried to reconstitute and eat them yet. I figured if I am hungry I can add them to rice,etc.

All Meats seem to work well. It is amazing how fragile meat becomes when completely dry, you have to handle it carefully or the strands pulverize and you have meat power. I fry hamburgers normally and cut the patties in half to fit in the jars right off the grill. The quicker you freeze, the more the flavor is locked in. Chicken and turkey work well and are easy.

I’m currently trying to freeze dry a bunch of canned tuna that is at its expiration date. It seems to mat together and the moisture comes out very slowly. We’ve decided to use it all in Tuna Helper and freeze dry that. It is kind of slow, but works pretty well.

Boxed mac and cheese works well, but I haven’t reconstituted it. I have eaten it dry and it tastes ok. American fried potatoes in the deep fat fryer with vegetable oil works great if you take the oil off after cooking. The fries taste like thick potato chips when dry, I used a bunch of last year’s potatoes after we planted this spring. I just cut off any rotten or black spots, sliced them and tossed them in the hot oil.

I don’t know about the ice crystal formation in smaller particles. Sounds like a good thing to try. I’ve found the freeze drying is quicker when you make smaller sized particles.

I recently bought a Savant vapor trap that gets down to -55 C that I want to try fruit on. The hole in the top is big enough to freeze a pint jar. I will let you know how it works when I get around to it.

I honestly think any vegetable will work to freeze dry if you don’t mind it being mushy when it reconstitutes. I have done green beans and raw peas, but haven’t reconstituted them. I think the reconstituted food will be like the same food if you froze it and then thawed it to eat later. We will do most of our green peppers this year, since we cook them anyway, if it does get mushy it won’t matter.

After drying we vacuum seal in bags and then put them in mylar bags in five gallon buckets.

I think it is a great process if you can find the equipment cheap. I have about $500 in my setup, but I found the flexidry at an auction cheap. I noticed in the link I sent earlier it says it works but the vacuum gauge is broken. The gauge is very important so you know when/if you are below the triple point.

[caverdude]

Triple point? Well, I think the veggies would be good either mashed and cooked or in soups. Yes I think any ground meat would freeze dry fine.

https://www.mandel.ca/products/sample_prep/Vacuum%20Concentration/Refrigerated_Vapor_Traps/index.html

Ok here it is and one gets down to -105c. But what do they cost? Looks like on Ebay, $600 to $2600 depending.

[Anonymous]

Is there any way to send a private message on this site?

[Anonymous]

The problem with the vapor trap I bought is, it doesn’t have a vacuum gauge.

this is the one I bought: https://www.analyticalinstrument.com/products/Savant-RVT100-Vapor-Trap.html I have yet to use it for anything, except freezing some peaches.

So you can freeze a jar just smaller than a mason quart, but there is no way to tell if you are maintaining vacuum when you start the “thawing” process.

The triple point of water is the point where ice either changes to vapor or water. With normal pressure, ice changes directly to water, it is above the triple point.

Below the triple point or under 6 mbar of vacuum, the ice cannot melt, it goes directly to vapor and is removed.

The only thing the vapor trap or flexi-dry actually does is remove the moisture from the vacuum line. It is to keep your vacuum pump from being ruined by the excess moisture.

All that is needed for freeze-drying is a strong vacuum and the “thawing” of the food. I stress “thawing” because it doesn’t really thaw. The food gradually warms and the energy liberates the moisture from the food.

[Anonymous]

Even the stringy meat freeze dries well. Turkey or chicken stripped from the bone dries quickly. I cubed up some cow tongue and cow heart in about 3/8inch cubes and it worked well.

[caverdude]

https://blog.larrydgray.net/2012/05/21/food-harvest-preservation/

Here is a blog post I just published which has a section at the end for the freeze drying that we have been talking about. Your additions to this threat spurred me into finishing this article.

[Author]

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