Lyophilization: Freeze-Drying
A Downstream Process


Reference: Snowman, John W. Downstream Processes: Equipment and Techniques, pages 315-351, 1988 Alan R. Liss, Inc.

Lisa Menyhart
Introduction to Biochemical Engineering
Professor Bungay

Biological materials often must be dried to stabilize them for storage or distribution. Drying always causes some loss of activity or other damage. Lyophilization, also called freeze-drying, is a method of drying that significantly reduces such damage. 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.

  1. COMPARISON WITH LIQUID-PHASE DRYING
  2. PPINCIPLES OF LYOPHILIZATION EQUIPMENT
  3. LABORATORY EQUIPMENT
  4. CHARACTERIZATION OF THE PRODUCT

Lisa Menyhart (menyhl@rpi.edu) / 6 December 1995 /