Freeze Drying

Harvesting and storing food is just as interesting as growing it. Freeze Drying is one way to preserve food. Let's take a look at it.

Freeze Drying

Freeze Drying is a process that eliminates water from substances like food or herbal preparations. There are three principal phases:

1. Deep Freeze (-40F)
2. Drop Pressure to Vacuum
3. Gradually Heat Food, sublimating water directly off substances and capturing it on outside of the freezer.

The machine takes the substance through these phases/temperatures a few times to complete the drying process.

After completion, the trays of freeze dried food are removed. All the water that was in the substance is now frozen to the inside of the freeze dryer. You can engage a "defrost" mode which uses the tray heaters to bring the chamber to 140F, which can blast through the defrost process in ~ 2 hrs. This can be accelerated greatly by manually breaking/pulling off the ice once the thaw starts a bit. This is the only critical step that has to be performed between loads.

Components

Corresponding directly to those three steps, there are three principal components in the freeze dryer:

1. Deep Freezer (lots of Amps)
2. Vacuum pump (lots of Amps)
3. Heated Trays (... lots of Amps)

As you can tell, these beasts draw quite a heavy load -- peaking at 16A when all three components are on (in practice, trays are only heated intermittently to gradually draw out hydration).

Tips

Freeze Drying Process

• The freeze dryer is typically tilted slightly back to drain off water.
  • When doing a load of liquids (i.e., raw eggs, yogurt, whatever), level the unit so liquid doesn't pour off the trays into the chamber.

• Food can be pre-frozen. This cuts ~ 6-8 hours off the cycle time, as the unit doesn't have to work for hours just to pre-freeze the substance. When pre-frozen, the unit will deep freeze further (-40F) for a bit, then skip directly to drying.

• Can cut one hour off cycle times by manually breaking/pulling out ice during defrost.

Storing

If properly dried and stored, food can stay good for 25 years.

• Use thick mylar bags (> 7mil). Thin ones are too fragile in general, and have a tendency to spring leaks if a freeze-dried piece of something or other is poked through.
• Vacuum sealing is not necessary (but will reduce size of stored food).
• Use appropriate big enough (300cc) oxygen absorbers. If in doubt, use more. You can't OVER-do it, but you can waste all your time and money and food if you UNDER do these.