As per freeze drying theory, raw product complete frozen is the first step. The freezing can be done inside a freeze dryer or in an external freezer. After that, move frozen product into drying chamber, the drying process will start.
A modern freeze dryer enables user program various steps in a recipe, and the freeze dry system fully automatic execute steps, one step finish, another automatic start, till drying end. For example:
- -30C 2hrs
- -20C 1hr
- -10C 1hr
- 0C 1hr
- +10C 2hrs
- +20C 5hrs
- +30C 10hrs
- +40C 2hrs.
You can program and storage hundreds of freeze drying recipes, for different product.
Freezing stage, freezing can be done in a deep freezer or in freeze dryer (if drying chamber with freezing function).
Primary drying, shelves temperature need raise slowly, too much energy may cause frozen product melt.
Secondary drying, shelves need a higher temperature (mostly is the ultimate that raw material can bear), the vacuum degree also high.
Freeze drying finish, if your secondary drying temperature is higher than +50C, before harvest need cool the chamber to +40C to lower, to create harvest condition, dried product with too high temperature have risk of damp.