Freeze drying

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. 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
Freeze drying4.

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 m
3
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)
oTg may be used to judge the stability of freeze
dried products.
oHigher the value of Tg , the more stable the
product is.
oThe value of Tg can be measured by DSC.
othe 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 freeze-
drying:-
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 energy-
consuming 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
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

Address: 67, Thiruvalluvar Street, Jagahambikai
Nagar, Ptadi , Chennai - 600050, Tamil Nadu,
IndiaPhone: 08377801581Website:
http://www.indiamart.com/subzeroindia/

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

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