Is a method of preserving food; see food
technology. The product is frozen, then put
in a vacuum chamber which forces out the ice
as water vapour, a process known as
sublimation. Many of the substances that give
products such as coffee their typical flavour
are volatile, and would be lost in a normal
drying process because they would evaporate
along with the water. In the freeze-drying
process these volatile compounds are mostly
retained.