DIY Freeze Dryer - I think it is possible

[gadget]

Hello,

I did some searching but not much info on the net on any DIY setups. I am planning on building a small scale freeze dryer and this is what I have so far as plans.

First, hurtles to over come are;
1 - suitable vacuum chamber. Would need to be able to heat the food inside for extra/final drying.

2 - Moister trap to keep water out of the vacuum pump

3 - Good strong vacuum pump 29.8 inhg or better

4 - cheap as possible parts.

For a vacuum chamber, I am considering either mason jars or a pressure cooker. Advantage of mason jars is being able to freeze the food with it easier due to smaller size. Also, may be able to use the sun to heat the food inside. Could daisy chain multiple mason jars with a manifold. Sealing would be easier then a pressure cooker. There are many other option too like PVC pipe.

Moisture trap. I have a line on an old upright deep freezer that works fine just looks really ugly and freezes up quick due to old door seals. I would gut the refrigeration parts and build the evaporator core into a vacuum chamber. The vacuum chamber is a problem for this one. I have not seen the size of the evap core, may fit into a pressure cooker(?) or maybe a keg or something. Could put some copper tubing into some PVC pipe maybe.

Vacuum pump. Vane pumps for a/c evacuation or getting cheaper but still pricey for a good one($200ish) Some window mount A/C units have a vane style pump that would pull enough vacuum but it would need to be modified for external cooling(more on this later). The common piston style pumps show some potential in series, but the vain style definitely will pull a better vacuum. Should be able to get one free or nearly free from a recycler.

For economy (less power) would install a vacuum reservoir and a high vacuum switch to cycle on and off as needed

Keeping power usage to a minimum is key here. I suspect this is part of the reason freeze dried food is so expensive. Thoughts or input???

[Bobbers]

The next, and biggest challenge, is the actual recipe needed for the individual foods. I looked into it at one point and decided, quickly, I'd leave this to the experts...
I'll save my diy efforts for things more in my areas of comfort...lol.

[gadget]

Originally Posted by Bobbers

The next, and biggest challenge, is the actual recipe needed for the individual foods. I looked into it at one point and decided, quickly, I'd leave this to the experts...
I'll save my diy efforts for things more in my areas of comfort...lol.

I was thinking more on the line of preserving fruit like raspberries or other simple food items. I had not even considered pre-done meals if that is what you mean.

[ForestBeekeeper]

Pressure-cookers are designed for holding pressure, not vacuum. I had a hard time trying to get one to hold vacuum.

[Wombat]

If you are looking to make a vacuum chamber then ya should take a look at prop forums. Those guys build that stuff all the time for molding and such.

[ForestBeekeeper]

Most full-serve florists have a Lyophilizer [freeze-dry machine].

Long-term shelf stable preservation of floral arrangements is one of the services that florists provide. Problem is that Lyophilizers start at $30k.

A florist we know has one, though she only uses it 2 or 3 times a year. Having one will never pay for itself. though it is seen as a feature that if you are lacking then you have to turn customers away and once turned away you will never see them again. So florists have them but rarely use them. You may be able to work out a deal with a florist to use theirs. But they will likely see you as a paying customer.

If you see a florist going out of business, that is your best chance to buy a Lyophilizer for your private use.

Over a year ago a Lyophilizer-salesman came by and gave me a sales pitch.

Using his numbers, I would have needed to be a much larger farmer to make the math work for me.

They freeze, including the trays inside of some models have their own cooling coils.

They suck a vacuum and dehumidify.

And they have fans inside to keep the air stirred. Apparently how well the air is stirred will cut operating time in half.

[gadget]

I just found a good youtube video of a guy doing some home freeze drying;

http://www.youtube.com/watch?v=mlywGYcY-tA

I've started collecting parts. I will update when I get a chance.

-Gadget

[MichaelK]

All of the freeze drying I ever did in the lab was in glass. You want to be able to see what you are drying to determine when all the ice has sublimed away.

Forget the idea of the vacuum reservoir for reducing power usage. You must maintain the same high vacumn throughout the whole process. A reservoir would simply lose it's vacuum from water vapor and negate it's purpose.

Why not go the simpler route of home canning in glass jars? All the equipment and expertise to do home canning is WIDELY available. Nothing has to be re-invented to get that done.

[gadget]

All of the freeze drying I ever did in the lab was in glass. You want to be able to see what you are drying to determine when all the ice has sublimed away.

That and plus the option to apply heat with a light source like the sun.

Forget the idea of the vacuum reservoir for reducing power usage. You must maintain the same high vacumn throughout the whole process. A reservoir would simply lose it's vacuum from water vapor and negate it's purpose.

What I want to do is cycle it between say 28.5 and 28.0 inhg. Vacuum pump would turn on at 28 and off at close to its max. The reservoir would allow for more time between cycles so the motor isn't going through lots of start cycles. I am really not sure if this would even work or not. It would be worth testing.

Why not go the simpler route of home canning in glass jars? All the equipment and expertise to do home canning is WIDELY available. Nothing has to be re-invented to get that done.

I already can and do lots of dehydrating. Works great.

[gadget]

And they have fans inside to keep the air stirred. Apparently how well the air is stirred will cut operating time in half.

That is interesting since there won't be much in there other then a few water vapor molecules cruising around. Maybe the fan is to help guide the water molecules to the vacuum pump????

The video I posted talked about the need for large vacuum tubes. Something I had not even thought about. I was originally planning on having all small tubing.

[gadget]

Just want to do and update on my progress so far;I will take some pics when I get a chance

- Mounted mason jar to 1 1/2" PVC tee. Manifold will consist of PVC pipe and tees.

- Took apart free 1960's freezer and recoiled evap line into a pressure cooker pot. Gathered up condenser lines into a smaller package.

- Picked up a Welch 1400 duoseal 2 stage rotary vacuum pump for $100

Here is my plans so far
6-12 mason jars hooked to PVC manifold. Cold trap made form deep freezer guts and a pressure cooker pot. High precision vacuum switches to turn on vacuum pump.

I am planing on having the cold trap coils at around -20F. I want to keep the vacuum in the range of 29.80 to 29.90. This would allow the water to freeze to the cold trap coils and sublimate at around 20F in the mason jars. Not sure how well it will work but this will be the first try. May have to go with a colder cold trap for a wider window of operation. Maybe a cascade system.

I ran the freezer after I took it apart and recoiled up the evap lines. It started to get really cold then got warm again. The system may be low on freon. Its R12 now, not sure if I am going to recharge it our try another freezer with a smaller compressor.

Will update more as project progresses

[Trilect]

DIY freeze dryer is doable.

One setup that I personally saw used a chest freezer, the freeze chamber was an American canner gasket less pressure cooker. The moisture trap was schedule 80 PVC with rounded caps and a very small drain valve on one side. The vacuum pump used was a homemade vacuum unit made from an ebay pump, two capped pieces of PVC pipe for vacuum reserve and a vacuum sensing switch that turned the pump on and off as needed.

Yes the chamber did leak a bit, but it did a fantastic job on fruits. Mainly strawberries (I tasted them) and flowers (not sure why they freeze dried flowers).

You can find the vacuum setup I mention on the web. Used for vacuum bag clamping of wood working projects.

I was told that you should keep the vacuum chamber relatively small 24 inches or less preferable less and use cast pots or pans or even boiler pipe.

[VonGhent]

How about using liquid nitrogen?

[ForestBeekeeper]

Originally Posted by VonGhent

How about using liquid nitrogen?

That could work for freezing, But you still need to do the drying.

[gadget]

I wanted to update this post with some progress. I have successfully freeze dried some ice cream and am almost done with the build. This is a beta version more or less. The temporary wood frame may get replace with a metal one. Most everything was sourced for free when possible to keep cost down

To finish, I still need to add the second row of mason jars and build the insulated box / cover that goes over the mason jar area. There will be 12 20watt halogen bulbs hooked up to a thermostat for second stage drying.

I swapped out the refrigerant for a lower temp. I was not sure if the -25c I was getting before was cold enough to condence moisture in the trap. Also bought a harbor freight vacumm pump to drop down my power usage and it works really good! boils water at room temperature all the way down past when it freezes.




Front view. There are 3 main levels. The mason jar area that will be insulated. The moisture trap made from 10" pvc and an evaporator from a refridgerator. The lower level with compressor, condensor and vacumm pump.




Side view shows access door with rubber gasket. This will be on hindges and will open so ice can melt off moisture trap after batch is run. The door is made from 4 layers of 1/4" plexiglass glued together with acetone.




Inside of moisture trap with door off. Top tube come from mason jars and has holes facing towards top for moisture to enter from. Bottom tube also has holes face downward. Cheap ebay temp sensor also in pic.




Side view showing other cover glued in place with silicone. Condensor is below it.


Things are progressing and I think I will have a working system soon. More updates to follow....

[IamZeke]

As someone who used vacuum chambers industrially, I see an issue in your future.

You are using a diaphragm pump. Just like small air compressors using diaphragms you have a very short lifespan. Nor are they very repairable.

You really want an oil sealed rotary vane pump, or oil bath pump for short. No flexible diaphragm to wear out and are far more repairable.

Brand new they aren't cheap, but you can pick up a good used rig usually on ebay for $200-300. You can also find steel vacuum chambers for about $150 used as well.

Yeah, about $400 or more for a good used setup, but life span will be measured in thousands of run hours instead of hundreds, which is the typical run for a diaphragm type. Plus when it finally gives out you can repair the oil bath, instead of having to toss the diaphragm style.

Use what you have now as proof of concept experimentation. Once you think you really understand the process and like your results then look to upgrade. In the meantime make a habit of watching ebay for the better pumps and chambers. You might get lucky one day and get one dirt cheap.

I also recommend you eventually upgrading to schedule 80 pvc pipe. You won't find that type at the hardware stores or home centers. But every decent sized town has someone selling it. Schedule 80 is institutional grade. Upgrading wall thickness ensures you have a far less chance of rupture.

Remember that vacuum creates a lot of stress in the components. A hard bump on a pipe under heavy vacuum can turn it into a implosion grenade. The pvc might only be plastic, but can be nasty when it's flying out in small shards at high speed. Those mason jars represent an even more dangerous situation. I highly recommend you putting up a stretched tarp screen around your experiment area, wearing full clothing and eye shields when you do this.

I'm not trying to discourage your experimentation. I think this is a worthwhile project for a prepper. But I also recommend upping your game a bit here. Use stronger pumps, materials, and proper safety protocols.

Yes, my suggestions raise the price. But once you begin pricing freeze dried foods in sufficient quantities for LTS then you are going to lay out a lot of money there too. With a good freeze dry rig you might be spending more upfront, but eventually it will pay itself back and begin saving good money over buying foods pre-made.

[bobsmith]

Originally Posted by gadget

- Picked up a Welch 1400 duoseal 2 stage rotary vacuum pump for $100

CAUTION - these old duoseals backstream like crazy - meaning once the pump has reached it's base pressure, oil will travel back from the pump, into all extremities of your vacuum system.

you should ahve a backstreaming trap between your pump and food, and or replace the oil in the pump with diffusion pump oil of the same viscosity (it will be much more expensive) as it has a MUCH lower vapor pressure and as such will lessen any potential backstreaming.

[gadget]

I am not using a diagram pump. I would love to see a diagram pump boil down water at near freezing temps. That would be impressive.

I am not using the Welch dual seal pump. I have used it and have not had a problem with the oil. There is a screen and back flow valve in the inlet at the top that prevents it. Don't know why you had a problem but these are proven pumps and well known in the scientific community. It worked well, just opted for the lower power of the smaller harbor freight pump.

[IamZeke]

My mistake. I was looking at the pictures only and thought I saw a hobbyist diaphragm pump there. That's what I get for not reading the whole thread.

I still would like to recommend schedule 80 gray pipe. I've seen schedule 40 implode under strong vacuum and was very happy I was wearing protective gear. A couple of my less careful coworkers weren't so fortunate and needed treatment for some ugly lacerations.

[gadget]

Its schedule 80. The hard part building a freeze dryer is the moisture trap and getting it cold enough. I am eventually going to convert the currrent refrigeration system into an autocascade.

Next project is a small -60c freezer for flash freezing and being able to crystallize food with high sugar content for freeze drying