Freeze drying is the process in which
water is removed from a product after it is
frozen and placed under a vacuum
allowing the ice to change directly from
solid to vapor without passing through a
WHY WE USE FREEZE DRYING
Removing water keeps food from spoiling
for a long period of time
Freeze drying significantly reduces the
weight of the food
PHASES OF FREEZE DRYING
Freeze drying process consist of three
During the freezing phase the goal is to
freeze the mobile water of the product
The rate of cooling will influence the
structure of the frozen matrix
Another important term related to freezing
is eutectic point
In this phase the chamber pressure is
reduced and heat is applied to cause the
frozen mobile water to sublime
It is important to control the drying rate
and heating rate during this phase
The length of the secondary drying
process will be determined by the product
The water content may be carefully
THE FREEZE DRYING PROCESS
Aspects of food stuffs
Mainly the freeze
dryer consists of 3
• Freeze drying
• Refrigeration coils
• Vacuum pump
Place the material to be preserved on the
shelf when it is still unfrozen.
Seal the chamber and process begins.
Compressor lowers the temp and freezes
the material and water is seperated.
Vacuum pump forces air out of chamber
and lowers the atmospheric pressure to
Small heat applied for ice to change
Due to low pressure ice turns directly to
water vapour and it flows out of chamber.
Water vapour condenses in freezing coil to
Process continues till material dries out.
Sublimation process accelerated to avoid
Once dried sufficiently – sealed in
moisture free packages.
As long as package is secure it can sit
without degrading for years and years.
Preserves color, aroma, taste, shape.
Transportation doesn’t require freezers.
Provide high quality product.
Increased handling and processing time.
Very costlier process.
Fire hazards if the chamber is not in
proper vacuum, while heater is on.
In pharmaceutical companies.
In flower industries.
For protecting old books.
The process is much cheaper for
Cost mainly depends on engineering skills
Quality of the product is very high.