It took 27 h to dry non-treated samples completely but moisture
content was reduced to 40% at 7 h. There was a sharp decrease in
moisture content up to 15% moisture content and then drying rate
and water removal slowed down because sublimated vapor passes
through a dry layer with increasing thickness over time and water
is progressively more bound at the end of the process as drying
proceeds. When only desorption of highly bound water takes place,
freeze-drying kinetics are very slow. Therefore, complete drying requires longer time.