This was a BASIC program that was published in
BINARY - Computing in Microbiology, 6: 19-20 (1994)
Freeze-drying, technically known as lyophilization, is a process of sublimation: water molecules in a solid phase specimen are directly converted to free water molecules in the vapor phase. The free water molecules are then trapped and removed from the process. Porous dried specimens usually are easily rehydrated. The purpose of freeze-drying is to increase the shelf life, or preserve a specimen, be it food, microbial organisms, or, in some circumstances to decrease the size of the product. Different temperatures and drying times are used to freeze and sublime different specimens, depending on the nature of the specimen. Because lyophilization is the most complex and expensive form of drying, its use is usually restricted to delicate, heat-sensitive materials of high value.
Substances that are not damaged by freezing can usually be lyophilized so that refrigerated storage is unnecessary. (Important exceptions are mammalian cells, nearly all of which are destroyed by lyophilized.) Many microorganisms and proteins survive lyophilization well, and it is a favored method of drying vaccines, pharmaceuticals, blood fractions, and diagnostics. Some specialist food products are also lyophilized. They rehydrate easily and quickly because of the porous structure left after the ice has sublimed. (The word lyophilized is derived from the Greek "made solvent-loving")
Occasionally materials are lyophilized to achieve a porous, friable structure rather
than for preservation. Lyophilizers are sometimes used for concentration of delicate materials.
The form of the product
and the type of container it is to be freeze-dried in influence the
type of lyophilizer needed and how it should be operated.