A Freeze Dryer You Can Build in Your Garage

What do trail mix, astronaut ice-cream, and cryogel have in common? This may sound like the introduction to a corny riddle, but they are all things you can make in your garage with a homemade freeze dryer. [The Thought Emporium] built his own freeze dryer with minimum fuss and only a few exotic components like a vacuum pump and a high-quality pressure gauge. The video is also posted after the break which contains a list for the parts and where they can be purchased.

Freeze drying uses a process called cryodesiccation or lyophilization. Below a certain pressure, water skips the liquid phase and goes directly to a gas, so frozen items can transition from ice to dry without a soggy step. When you jump the liquid phase, objects hold their shape when they were frozen, and since no heat is used, you don’t carmelize your sugars.

A freeze-dryer like this has three parts. The first is the pump which doesn’t need any explanation. Next to the pump there must be a water trap. This chilly compartment recondenses the water vapor, so it doesn’t get inside the pump or saturate the things you’re trying to dry. Lastly, there is the drying chamber where your items are placed to have their moisture taken out.

Astronaut ice cream has been made on Hackaday before. [The Thought Emporium] has also been seen including a piece on making your own graphene.

23 thoughts on “A Freeze Dryer You Can Build in Your Garage

  1. Cool project but I suspect the fly in the ointment for most people is going to be the vacuum pump. And after watching the video, if it takes 16 hours for the process to run I suspect the dry ice bill gets expensive too. One of those things I would love to see done just because it is neat, but I don’t think I will be building my own rig soon.

    1. Dry ice is cheap, you can often find it in grocery stores for a few dollars a pound. If your crushing it obviously its gonna sublimate off faster. But If you leave it in block form in a well insulated environment, than its going to maintain its mass fairly well.

      I would say instead of using an alcohol base use acetone, as most isopropyl and denatured alcohols start to free around -50c, which then insultates itself keeping it from getting any colder. The Acetone will still a liquid till around -85c (it will slowly get conaminated with co2 and water and turn to a solid after a while if keep at these temps. But you will achieve a much lower temp and more effeicently transfer heat between the pots.

      I would also recommend looking at using Neoprene as insulator as well. Closed Cell neoprene makes a great insulator for cryo materials. Its much easier to work with as well. You can always use old wetsuits too. (though i would keep that old wet suit away from the food end of things, not so tasty)

      1. What actual purpose is dry ice sold for in grocery stores in the USA ?
        I’m curious why it’s possible to buy a sack of potatoes in the same store as dry ice as if it’s a normal thing to be buying every day.

        It’s not easily available here in the UK.
        Likely a trip to checmical supplies company or something like that.
        You can buy over the internet quite easily, shipping next day in a big ploystyrene container.
        It aint cheap.

    2. A repurposed refrigeration pump should be enough, it doesn’t require the hard vacuum of space.
      I did a gig doing food inspection while back at school and one of my stops was Oregon Freeze Dry, huge place. I was surprised that while nearly everything starts out LN2 cryo-frozen and then conveyor lined right into the chamber or trucked in at a more normal frozen temp the chambers over time bring up the temp to sometimes 40c or more, it has been over 15 years so I can’t recall the exact vacuum readings used.

      1. True, Aerogel typically means foams made using super critical CO2. A fair point.

        Typically when a solvent is removed by freeze drying, you create a different mixture than when you make an aerogel, which does involve super critical CO2. Unclear how the term Cryogel is also a registered US trademark at least if it is also a generic term though (though not for super critical CO2 based foams).

        *shakes head*

  2. As a heads up for anyone who isn’t aware, don’t glue polystyrene with super glue it dissolves.
    Oh and some fabrics have a tendency to spontaneously combust. Sometimes useful, not so much if you spill it on your clothes :D

  3. I don’t understand the necessity for the water trap?

    I remember some article here or perhaps popular mechanics or perhaps some diy vacuum tube builders technique for pulling a relatively strong vacuum: using a strong flexible tube and a roller, like a peristaltic pump.

    So just put the object to be vacuum dried in the vessel, and use a peristaltic pump to draw out gas lowering pressure until any water starts to boil, at which point the pressure remains constant (if the vessel is in thermal equilibrium with room temperature, so having low thermal resistance between inside and outside of the vessel, say using heat pipe for room temperature), at that point you are pumping out water vapor (which will simply turn into water and heat as it leaves the pump at atmospheric pressure, preferably this heat is exchanged with the heat pipe), as soon as the pressure drops below the boiling point of water at the temperature inside the vessel you know you have extracted most water. Temperature and vacuum gauge pressure sensors for pcb mount are cheap.

    1. You only need vacuum, but maintaining a deep vacuum is really hard. At very low pressures even small amounts of liquid become huge volumes of gas. This is overwhelming for the pump. While the pump may eventually break, even if it does not, you are unlikely to stay at the pressures you want for freeze drying.

      If all you want to do is dehydrate your food, use higher temperatures and it can happen really fast (food dehydrators usually go in the oven), freeze drying is all about maintaining the item at a temperature below which it will not degrade during the process. If you want to keep your item at -20C, sublimation pressure is just 1mBar, and if you want to take the water out at any speed, you need the surrounding pressure to be around half of that, or 0.5mBar. Maintaining 0.5mBar while also trying to exhaust hundreds of liters of water vapor is difficult. If you keep a cold trap at say, -60C, the sublimation pressure is only 0.01mBar. Almost all of the water vapor will freeze back as a solid in the trap, and the pump will not have to work nearly as hard.

  4. So I stumbled across this as a random idea. Ive seen everyone having the the two hoses at the top of the condenser tank. Couldnt you have the pipe from the food tank enter the bottom or side then have the vac pump hose at the top? then in the condenser tank have a coil or conductor type sync to encourage condensation? This is to encourage the gas vapor to actually pass through something rather then having the entrance and exit so close to each other? Im not educated on this so Im just asking for ideas.

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