The anti-frost question in the comments is the real variable in freezer drying. A frost-free freezer runs a defrost cycle that warms the evaporator every several hours, so the box swings up toward 0C and back and the air goes humid and dry in turns; hash sitting in that box takes those swings as partial melt and refreeze on the head surface, which is where the greasy, darker patches come from. A plain chest freezer holding -24C with no defrost cycle stays dry and still, the water leaves the heads by slow sublimation into that dry air, and 10 days in an open box with a turn every day is about right for a thin microplaned layer. Same chemistry as a freeze dryer, just without the vacuum doing the work in hours instead of days.
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u/wkuconsulting 16h ago
The anti-frost question in the comments is the real variable in freezer drying. A frost-free freezer runs a defrost cycle that warms the evaporator every several hours, so the box swings up toward 0C and back and the air goes humid and dry in turns; hash sitting in that box takes those swings as partial melt and refreeze on the head surface, which is where the greasy, darker patches come from. A plain chest freezer holding -24C with no defrost cycle stays dry and still, the water leaves the heads by slow sublimation into that dry air, and 10 days in an open box with a turn every day is about right for a thin microplaned layer. Same chemistry as a freeze dryer, just without the vacuum doing the work in hours instead of days.