Freeze drying In a typical phase diagram , the boundary between gas and liquid runs from the triple point to the critical point . Freeze drying ( blue arrow ) brings the system around the triple point , avoiding the direct liquid-gas transition seen in ordinary drying ( green arrow ) . Freeze drying ( also known as lyophilization ) is a dehydration process typically used to preserve a perishable material or make the material more convenient for transport . Freeze drying works by freezing the material and then reducing the surrounding pressure to allow the frozen water in the material to sublime directly from the solid phase to gas . The greatly reduced water content that results inhibits the action of microorganisms and enzymes that would normally spoil or degrade the substance . The application of partial vacuum speeds sublimation making it useful as a deliberate drying process . A cold condenser chamber and/or condenser plates provide a surface ( s ) for the water vapour to re-solidify on . This condenser plays no role in keeping the material frozen ; rather , it prevents water vapor from reaching the vacuum pump , which could degrade the pump 's performance . Condenser temperatures are typically below −50 °C . If a freeze-dried substance is sealed to prevent the reabsorption of moisture , the substance may be stored at room temperature without refrigeration , and be protected against spoilage for many years . Freeze drying causes less damage to the substance than other dehydration methods using higher temperatures . Freeze drying does not usually cause shrinkage or toughening of the material being dried . In addition , flavours and smells generally remain unchanged making the process popular for preserving food . Unfortunately , water is not the only chemical capable of sublimation and the loss of other volatile compounds such as acetic acid ( vinegar ) and alcohols can yield undesirable results . Freeze-dried products can be rehydrated ( reconstituted ) much more quickly and easily because it leaves microscopic pores . The pores are created by the ice crystals that sublimate , leaving gaps or pores in its place . This is especially important when it comes to pharmaceutical uses . Lyophilization can also be used to increase the shelf life of some pharmaceuticals for many years . The process ha s been popularized in the forms of instant coffee , and freeze dried ice cream ; an example of astronaut food . It is also popular and convenient for hikers because the reduced weight allows them to carry more food and reconstitute it with available water . In high altitude environments , the low temperatures and pressures can sometimes produce natural mummies by a process of freeze-drying . In chemical synthesis , products are often lyophilized to make them more stable , or easier to dissolve in water for subsequent use . Recently , some taxidermists have begun using freeze drying to preserve animals . External links http : //home.howstuffworks.com/freeze-drying.htm/printable http : //inventors.about.com/library/inventors/blfrdrfood.htm http : //www.fda.gov/ora/inspect_ref/igs/lyophi.html http : //www.rpi.edu/dept/chem-eng/Biotech-Environ/LYO/index.html http : //www.technalysis.us/freeze_dry_software.htm / CAE freeze drying processes See also Food preservation Supercritical drying Categories : Dried foods | Food preservation | Unit operations In other languages : Dansk | Deutsch | Español | 한국어 | Italiano | Nederlands | 日本語 | Polski | Svenska | Português 