The freeze-dry process was developed during World War II because of huge problems with the supply
of vaccine and serum, and keeping them chemically stable without the need of refrigeration. It was
mainly used to freeze organic or inorganic materials as well as liquid or fluid substances. Usually this
process is done in a vacuum and evaporation chamber with low temperature and very low pressure to
create an environment with the optimal conditions for the sublimation phase, to turn a frozen and solid
material immediately into gas. (sublime means evaporate) E. P. Abraham suggested in 1941 that the only way to evaporate the aqueous solution of Penicillin to
dryness and without loss of activity was to use the freeze-drying method. (evaporation in vacuo from the frozen state) Penicillin-rich solution will evaporate at a very low pressure inside of the vacuum chamber.
The frozen watery The first step would be to lower the temperature very slowly to about -50°C. The slower the rate at which the freezing process is undertaken, the bigger the crystals produced and the larger the amount of remaining Penicillin sodium salt.
A decreasing of the pressure to just a few microbars is the next step to pass the range of the sublimation
phase. About 95% of the frozen water will be sublimated (evaporated) during the first drying process.
It is necessary to remove the unfrozen water molecules additionally with a second drying-process. The
remaining content of water of the finally freeze-dried product is about 1-4%.