Today, I'm making a super cheap freeze dryer to create some unique ingredients for the Australian Barista Championships in 4 weeks. I’ve learn a lot within these walls and thought I'd share the process in case anyone else wants to give it a go
This is based upon the youtube build video here
http://t.co/x1xujfM2C9 but with a couple of Australian-ised materials and equipment. All of this would undoubtedly be easier with McMaster Carr and Walmart around the corner - lucky Americans!
So a freeze dryer is essentially 3 main components in series:
1. A vacuum pump that can pull a decent high vacuum
2. A condenser that freezes the water and some gases before they can enter/damage the pump
3. A chamber for the foodstuff that can be warmed to ~40C
The idea is to sublimate the water in the foodstuffs so it misses the liquid phase and goes straight to gas. If you've ever been lucky enough to see a a comet's tail, that's sublimation at work
Here's what you'll need:
Vacuum Pump - (this is the biggest expense, but absolutely necessary)
Two chambers that can withstand high vacuum (16 psi all over the exterior, which can add up to a tonne. I chose stainless bowls with a flat topped lip for a higher chance of a successful seal.)
Metal bowl that fits around your condenser chamber with room to spare
Thick Aluminium or Perspex plate (off cuts from a local plastics engineer or machine shop)
Silicone Sheet for Gaskets (3mm from a gasket wholesaler. Silicone baking sheets should work too!)
Insulating Foam (anything that’s super low density)
Isopropyl Alcohol and Dry Ice OR Liquid N2 (isopropyl is liquid down to -89C and assists thermal transfer from dry ice to the chamber)
Reinforced hosing (refrigeration lines are a good bet here. They have nice fittings on the ends which makes construction much easier)
Vacuum-proof valve (an HVAC supplier will have nice fittings designed for AC lines)
Pressure Gauge (not 100% necessary but nice to diagnose leaks)
Tools to drill and tap thread into the plates
Refrigeration hose barbs, fittings etc.
Plastic for a condenser dividing wall
Once you have everything, it’s a pretty simple assembly job.
Slice insulating foam to create a cold box for the condenser. This is a passive system so the better it's insulated, the less dry ice I have to buy. I went all out and even made a lid with hose holes.
That steel bowl will hold the dry ice and isopropyl.
Measure out the chamber diameters for gasket slicing.
Mark, drill and tap holes for fittings
Insert fittings with teflon tape
Cut and fit divider plate. This will force all gas close to the condenser surface before moving towards the pump.
Connect vacuum to each chamber individually to check for leaks.
Connect the whole system together, pull vacuum, close the valve and see how long it can hold for. It should be so slow that you can’t see the needle move. If you can, there’s a significant leak somewhere!
Then it’s game time!
I haven’t bought dry ice just yet, so I’ll add any lessons I learn or sweet results in this post once I do!
