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3.
Freeze-Drying Process
The freeze-drying process is divided into three stages: freezing, main drying, and final drying.
Freezing
The freezing stage duration varies depending on the food's type, weight, and thickness, taking
anywhere from 6-15 hours for unfrozen food and 2-4 hours for frozen food. During this stage,
the cold trap temperature drops gradually to around -40F, and only the compressor runs. Frost
may be visible on the interior chamber surface, and condensation may form on the acrylic door
and gasket.
Main drying
The main drying stage begins automatically when the preset freezing time, shelf temperature,
or food temperature is reached, as explained in the Auto-freeze-dry-setting in Section 10.
Alternatively, you can start the drying process by pressing the 'Drying' button. The vacuum
pump operates for a set duration at the beginning of this stage, and the chamber pressure
drops to or below 550mTorr. The heater is then turned on to maintain the pressure at the initial
target pressure, and the patented freeze-drying algorithm is initiated.
During the constant-pressure phase, the pressure remains constant, while the shelf
temperature gradually increases. Once the target shelf temperature is reached, the algorithm
enters the constant-temperature phase, during which the shelf temperature is maintained at a
constant level, and the vacuum pressure gradually decreases. This cycle repeats until the
maximum shelf temperature is reached.
The compressor, vacuum pump, and heater are all running continuously during the main drying
stage, and ice rings may appear on the chamber's interior surface.
Final drying
The final drying stage begins when the maximum temperature is reached or when a preset food
temperature measured by the temperature probe is reached (if the probe is in use). These
indicators suggest that most of the moisture has been extracted from the food. The default
final dry duration is seven hours. The drying algorithm adjusts the final dry time automatically
when the temperature probe is in use. Extra final dry hours can be added manually if necessary.
During the final drying stage, the compressor, vacuum pump, and heater operate similarly to
the main drying stage. When the drying is complete, the heater and vacuum pump are turned
off, and the compressor continues running to keep the chamber cool.
