I would like to make vacuum freeze-dried food at home for fun.

Ben at Applied Science made it look easy.

• 2-stage 1 HP Vacuum pump,
• Chamber,
• Strawberries,
• Raspberries,
• Mangoes,
• Kiwi fruit,
• Rainbow ice cream.

The vacuum pump pulls a low vacuum, about 50 mbar. The cold trap is filled with methylated spirits and dry ice. This brings it to around -75°C. The water ice in the food sublimates directly to a gas without disturbing the macro-scale structure of the food. I.E. The ice cream doesn't melt - it maintains its structure and becomes dry. The gaseous water travels along the tube and condenses in the cold trap.

Ideally the food should be at or below -35°C when it goes into the vacuum chamber. My freezer only goes to -20°C, so I have boxed and bagged portions of the food separately so I can superchill them in the cold trap before putting them into the food chamber. I have a temperature-controlled hotplate on standby to put some heat into the system to kick off the sublimation. I will pre-chill the food chamber too, so the ice cream doesn't start to melt as soon as it hits the stainless steel.

The pump gets hot during operation, I estimate around 65°C, so I set up a few PC case fans to help it shed heat.