Freeze drying, also known as lyophilization, is a process that removes water from frozen materials by converting frozen water directly into vapor without forming liquid water in between. It works through the phenomenon of sublimation where water passes directly from solid to vapor state below the triple point of water. The main steps are initial freezing of the material, drying where heat is applied under high vacuum to sublime the ice crystals into vapor, vapor removal through condensation, and storage of the dried material. Freeze drying is used to preserve foods and pharmaceuticals, increasing their shelf life, and allowing them to be stored without refrigeration.

1. FREEZE DRYING
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2. introduction
 Freeze drying is a process whereby water or other solvent is
removed from frozen material by converting the frozen water
directly into vapor without the intermediate formation of liquid
water. Freeze drying also known as lyophilization.

3. PRINCIPLE
 The main principle of freeze drying is a phenomenon called
sublimation. where the water passes directly from solid state to the
vapour state without passing through liquid state.
 Sublimation of water can take place at pressures and temperature
below triple point i.e. 4.579 mm of Hg and 0.0099 degree Celsius.

4. STEPS IN FREEZE DRYING
 Initial freezing : The materials which are to be freeze dried are frozen
to a temperature at which no liquid phase is present. The
temperature required for freezing is different for different types of
food depending on their chemical composition. But in general -
60°C ensure complete freezing
 Drying : The frozen products are taken into a high vacuum drying
chamber and heat is supplied to remove the ice crystals formed
due to freezing. Byte application of heat, the ice crystals change
directly to vapour without going through a liquid phase because of
high vacuum. The ice sublimes below the pressure of 4.7 mm of Hg.
The heat required for sublimation is supplied directly to the foods
from the source by radiation.

5.  Water vapour removal : It is necessary to remove the water vapour to
make the food perfectly dry. The water vapour formed is pumped out
of the chamber and is brought in contact with refrigerator coils where it
again forms ice crystals. The collected ice can be removed by heating
with the steam. The ice turns in to water and is drained out.
 Storage and Packing : After removal of moisture, the packing of the
food stuff is done either in vacuum or in the presence of inert gas. It
prevents contamination of the product by pollutants in the air and
prolongs the lifeof the product. Freeze dried foods can be stored with
out refrigeration inthe air tight dry containers for months. This type of
food normally used bynavy, military and people working on ships.
 Reconstitution : The consumer has to reconstitute the freeze dried
foody mixing with water to the required extent. Now it regains its
flavored retains very nearly to the original fresh condition and ready for
consumption. The off-seasonal vegetables and fruits can be made
available to the consumer all round the year.

6. Equipment
 The main components of freeze drying equipment are.
 Refrigeration system
 Vaccum system
 Control system
 Product chamber or manifold
 condesner

7.  Refrigeration system - cools the condenser located inside the freeze dryer. It
also cool shelves in the product chamber for the freezing of the product.
 Vacuum system - consists of a separate vacuum pump connected to an
airtight condenser and attached product chamber.
 Control systems - include temperature and pressure sensing ability.
Advanced controllers use the programming of a complete “recipe” and
monitor freeze drying process. It depends on the application and use.
 Product chambers - a larger chamber with a system of shelves on
which to place the product.
 Condenser – It is to attract the vapors being sublimed off of the
product. The sublimated ice accumulates in the condenser.
temperature of the condenser substantially below the temperature
of the product

8. APPLICATIONS
 Pharmaceutical companies use freeze drying to increase the life of
products such as vaccines and other injectbles
 Freeze drying is used to preserve the food and make it very light
weight
 Bakery and confectionary
 Fish,Meat etc.

9. Advantages
 Light weight which reduces the cost of shipping
 Requires no refrigeration storage cost reduced
 Reconstruted quickly by adding water
 Have long shelf life when packed
 Physical structure of food is not altered

10. Disadvantages
 Engineering skills for production
 Advanced technology
 Increased handling processing time
 Freeze-drying costs about five times as much as conventional
drying.

11. THANK YOU…