ABSTRACT
Freeze drying is accomplished by reducing the product
temperature so that most of the product moisture is in a
solid state, and by decreasing the pressure around the pro-
duct, sublimation of ice can be achieved.[1] Developments of
freeze drying owe much to advances in vacuum pumping
and refrigeration machines since the late 19th century. Yet
freeze drying had been regarded as an occasional scientific
tool until Flosdorf started his study on its industrial applica-
tions to food drying[2] and pharmaceutical drying[3] in
1930s. Since then, research and development in freeze dry-
ing of foods were promoted for military and commercial
purposes in the United States and several European coun-
tries, and then in the beginning of 1960s, these results,
including the process of accelerated freeze drying (AFD)
method,[4] were released to industry for commercial
PROCESS, EQUIPMENT, AND COSTS
Freeze Drying Process
Fig. 1 shows a typical freeze drying process for manufac-
turing an instant coffee, together with temperature profiles
of the product during the period of main freeze drying
operations: prefreezing, primary drying, and secondary
drying. It should be noted that all of them are not mechan-
ical, but thermal unit operations.
