Freeze Drying of Food

1. FREEZE DRYING

2. Freeze Drying
• Freeze-drying also called as Lyophilization
• It is a process in which material is freeze then high-
pressure vacuum is applied to sublimate the water in
the form of vapour
• Process was first applied to food products after the
Second World War
• Coffee was first freeze dried food products to be
produced, but now vegetables, fruits, meats, fish, dairy
products, herbs and food flavorings can be freeze dried

3. Principle
• Based on Sublimation, where water passes directly
from solid state (ice) to the vapor state without
passing through the 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.
• Material to be dried is first frozen and then subjected
under a high vacuum to heat; frozen liquid sublimes
leaving only solid ,dried components.

4. * Lyophilization is carried out below the triple point to enable conversion of
ice into vapor, without entering the liquid phase (known as sublimation).
Phase diagram of water

5. Steps in Freeze Drying
Pretreatment
Freezing
Primary Drying
Secondary Drying

6. • Pretreatment - method of treating the product prior
to freezing. include concentrating the
product, formulation revision, decreasing a high-vapor-
pressure solvent, or increasing the surface area.
• Freezing - The product is frozen. This provides a
necessary condition for low temperature drying. freezing
temperatures are between −50 °C and −80 °C

7. • Primary Drying - pressure is lowered, and enough
heat is supplied to the material for the ice to sublime.
This phase may be slow because, if too much heat is
added, the material's structure could be altered.
• Secondary Drying - to remove unfrozen water
molecules, since the ice was removed in the primary
drying phase. In this the temperature is raised higher
than in the primary drying phase, to break any physico-
chemical interactions that have formed between the
water molecules and the frozen material

8. Equipment
The main components of freeze drying
equipment are:
 Refrigeration System
 Vacuum System
 Control System
 Product Chamber or Manifold
 Condenser

9. • 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.

10. • 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.

12. Heat & Mass transfer
 There are 3 methods of heat transfer
 Through frozen layer
 Through dried layer
 Heating by microwaves
 When heat reaches sublimation front, it raises
temperature and water vapour pressure of ice,
vapour then moves through dried food to region of
low vapour pressure in drying chamber.

13. Application
• Fruits & Vegetables
• Beverages
• Dairy Products
• Meat
• Fish
• Spices & herbs
• Bakery & Confectionery

14. Advantages
• Lightweight, which reduces the cost of shipping.
• Requires no refrigeration, storage costs are reduced.
• Physical structure of the food is not altered, food
retains much of its color, shape, texture, and flavor
when it is prepared for consumption.
• Reconstituted quickly and easily by adding water.
• Have a long shelf life when packed properly.

15. Conclusion
• The freeze-drying process is expensive, which
restricts its application on wide range in the food
industry.
• New technical solutions are applied to modify the
freeze-drying process and make it time- and cost-
effective.
• It is suitable for high value products with specific
biological and phytochemical properties