Freeze drying, also known as lyophilization, is a process used to preserve food by removing water from it after freezing. It works by freezing the food, lowering pressure, and slightly increasing temperature to allow the frozen water in the food to sublimate directly from solid to gas. This preserves the food's structure, biological and chemical properties better than conventional drying. Freeze drying is a multi-stage process involving freezing, sublimation drying, and desorption drying. It results in food that can be stored for long periods without spoiling and rehydrates easily. While it maintains high nutrient and sensory qualities, freeze drying is an energy-intensive process with high initial equipment costs.

1. 1.FREEZE DRYING
Submitted by:Aarti Nimesh(FPEM/213001)

2. 2.INTRODUCTION
• Food freeze drying is a dehydration process in which
the water in food is frozen, and then sublimated
directly from the solid phase to vapor by heating
under vacuum.
• Freeze Drying preserves the integrity of the product’s
biological and chemical structure and activity.
• Chemical decomposition is minimized since drying
takes place at low temperature.

3. 3.Theoretical Basis of Freeze Drying
• At the triple point
(0.0098°C and 4.58
mm Hg), ice , water
and water vapor
coexist in equilibrium..

4. 4.
Freeze drying
Normal (right) and freeze-dried (left) spaghetti
Completely remove water from some material, such as food, while
leaving the basic structure and composition of the material intact
Two reasons
 Keeps food from spoiling for a long period of time
 Significantly reduces the total weight of the food
How?
 Freeze the material
 Lower the pressure (<0.006 atm)
 Increase the temperature slightly

5. 5.Heat transfer during freeze drying
• Heat transfer through the frozen layer
• Heat transfer through the dried layer
• Heating by microwave

6. 6.Mass transfer during freeze drying
• When heat reaches the sublimation front, it raises the
temperature and the water vapor pressure of the ice.
Vapor then move through the dried food to a region
of low vapor pressure in the drying chamber.
• 1 g of ice forms 2 m3 of vapor at 67 Pa.

7. 7.

8. 8.Freeze drying process
3- stages: freezing/Solidification:- Cooling the material
until completely frozen.
Sublimation drying:- Sublimation of ice from
product reducing pressure in the chamber and
providing heat to the product.
Desorption drying:- Desorption of residual
moisture from the product

9. 9.Freeze drying process

10. 10.Process overview
• Vials are aseptically
filled with the solution
or suspension to be
freeze dried and
partially stoppered with
a special rubber closure
that allows to escape the
water vapor.

11. 11.Schematic diagram of freeze drier

12. 12.Glass transition temperature (Tg)
o Tg may be used to judge the stability of freeze
dried products.
o Higher the value of Tg , the more stable the
product is.
o The value of Tg can be measured by DSC.
o the storage temperature should be at least 20K
lower than its glass transition temperature.

13. 13.Types of freeze dryers
Conduction type: Contact freeze dryers
 Accelerated freeze dryers
Radiation type: Radiation freeze dryers
 Microwave and dielectric freeze dryers

14. 14.Vacuum pump for freeze drying
Tasks and characteristics of vacuum pumps in freezedrying: Removing air and other non-condensable gases leaking into
the drying chamber from atmospheric environment.
 Removing air and other non-condensable gases released from
the materials in the drying chamber.
 In a freeze-drying system, the commonly used vacuum range
is from 1 Pa to 10 Pa.

15. 15.Advantages of freeze dried food
(1) Very high retention of sensory characteristics and nutritional
qualities and a shelf-life longer than 12 months when correctly
packaged.
(2) Freeze-dried food is porous and easy to be rehydrated and
instantly dissolved. It can be consumed directly or after
rehydration.
(3) Aroma retention up to 80 – 100 %
(4) No additives are added into the food during the freeze drying
process.
(5)The texture of freeze-dried foods is well maintained; little
shrinkage and no case hardening.
(6)Only minor changes to proteins, starches or other
carbohydrates.

16. 16.Disadvantages of freeze dried food
 Freeze-drying is a time-consuming and energyconsuming process, which lead to higher product
costs of freeze-dried food.
 Freeze drying system includes vacuum and
refrigeration equipments. The initial costs are
relatively high.
 The open porous structure of the food may allow
oxygen to enter and cause oxidative degradation of
lipids (packaging in inert gas necessary)..

17. 17.Examples of freeze dried foods

18. 18.

19. 19.Recent advancements in freeze
drying
Atmospheric freeze drying:
Dr Harold Meryman is considered the inventor of the science
of atmospheric freeze drying.
 Compared to vacuum freeze drying reduce the energy consumption compared to vacuum freeze
drying while maintaining a high product quality.
 the temperature is higher, typically in the range of -3 to -10C.
 improved heat and mass transfer between circulating drying
medium and the frozen sample.
 high quality and homogeneous quality properties of the dry
product with an increased retention of volatile aromatic
compounds.

20. 20.CONT….
 uses heat
pump
systems in
combination with a
fluid bed dryer.
The heat pump
dehumidifies the air,
condenses the water
vapor and conserves
the heat.
There is a very high
mass-and-heat
transfer.

21. 21.Advantages of atmospheric
freeze drying process
 Low initial investment cost since expensive vacuum
auxiliary equipment could be eliminated.
 The process could be designed as a continuous
system with higher productivity and lower operating
cost.
 The application of a heat pump system and different
process temperature elevating modes in AFD would
decrease energy consumption and drying time.
 Inert gas drying environment such as nitrogen or
helium can be applied to minimize the product
degradation caused by oxidation.

22. 22.Suppliers of
freeze driers
Address: UG- 37, Vishal Tower, District
Center, Janak Puri, New Delhi - 110058,
Delhi, IndiaPhone: 08586979463
Website: http://www.accumax-india.com/
1.Accumax India, New Delhi
features-
Coming fitted with 100 liters/ min
double stage rotary vane type vacuum
pump with air ballast providing for
vacuum of 1x10-3 torr on pump head.
High accuracy maintained in
temperature control through use of
microprocessor based digital temperature
indicator cum controller.
Temperatures range up to (-)40° C at
ambient temperature of 20° C.

23. 2. Sub Zero Lab
Instruments, Chennai
Address: 67, Thiruvalluvar Street, Jagahambikai
Nagar, Ptadi , Chennai - 600050, Tamil Nadu,
IndiaPhone: 08377801581Website:
http://www.indiamart.com/subzeroindia/
FeaturesWell-arranged ports for
convenient placement of
flask.
Efficient dual stage
rotary vane vacuum pump
Castor wheels for easy
movement
Available in two models
-55°C and -85°C
Safety cut-off for
vacuum pump
Easy cleanable trap and
drying chamber

24. •
3. SGM Lab
Solutions, New Delhi
Features:
Light weight.
Energy Efficient.
Low maintenance.
Address: BA- 15, Mangolpuri Industrial
Area, Phase- 2 , New Delhi - 110034, Delhi,
IndiaPhone: 08376808239Website:
http://www.laboratory-equipments.in/

25. 25.Conclusion
 A freeze dried product with the best attributes and
quality.
 In freeze drying, minimal structural changes or
shrinkage.
 In freeze drying process, nutrients are largely
retained.
 Freeze drying system includes vacuum and
refrigeration equipments. The initial costs are
relatively high upto 4 times than conventional drying.

26. Reference
 Atmospheric Freeze Drying—A Review
I. C. Claussen a , T. S. Ustad a , I. Str⊘mmen a & P. M. Walde
a )Department of Engineering Science and Technology,
Norwegian University of Science and Technology,
Trondheim, Norway
b )SINTEF Energy Research, Kolbj⊘rn Hejes vei 1D,
Trondheim, Norway Published online: 16 Jun 2010.
 http://dir.indiamart.com/impcat/freeze-dryers.html