Click here to view a
Process - Freeze Drying
Steps in Freeze Drying:
Primary Drying
Secondary Drying
Filter Integrity Testing
Leak Test
Website sponsored by Millrock Technology, Inc
The 3 major parts of a freeze drying recipe include freezing, primary
drying (sublimation), and secondary drying (desorption). Each step
is critical in producing the required end product is critical in
producing the required end product.

Freezing may be the most under-rated step. Proper freezing will
ensure a good cake, while improper freezing may result in a
product that cannot be successfully freeze dried. The typical
objective of freezing is to produce a frozen matrix with sufficient
crystal structure to allow the sublimating material to escape. The
larger the crystal the better. Slow freezing produces larger crystals.
Some products form a glassy material and annealing may be
required during the freezing process. Annealing, first lowering the
temperature then raising the temperature and then lowering it
again, locks the constituents in place and then allows the crystals
to grow. Freezing can range from 1 hour to 24 hours, depending on
the application.

Primary drying (sublimation) drives the unbound moisture out of
the product. Sublimation occurs under vacuum with the product
temperature below its critical temperature. This is typically the
longest process. At the end of the primary drying cycle, the product
will have 3 to 5% moisture content.

3- Secondary drying (desorption) drives the ionically bound water
from the material. This is done by heating the product. Secondary
drying can result in moisture levels of 0.5%.
Copyright 2009