This document discusses dehydro freezing or freeze drying, which is a method of preserving perishable materials like food and pharmaceuticals. It involves freezing the material and then applying a vacuum so that the frozen water sublimates from solid to gas without passing through the liquid phase. Freeze dryers are used to remove water through sublimation in an industrial setting. They have components like a vacuum chamber, vacuum pump, condenser, temperature and pressure sensors, heating source and control system to carefully monitor and control the freeze drying process. Various types of freeze dryers exist for different applications. Freeze drying is useful for preserving foods like fruits, vegetables, coffee, eggs and meats as it retains nutrients, taste and texture better than other preservation

1. DEHYDRO FREEZING
SUBMITTED TO
Dr. Anil Kumar Chauhan
DSFT, BHU.

2. INTRODUCTION
• Dehydro freezing is also known as the freeze-
drying it is a method of preserving perishable
materials such as food, pharmaceuticals, and
biological samples by removing water from the
material through the process sublimation.
• The process involves freezing the material to a
very low temperature and then subjecting it to a
vacuum.
• Under vacuum conditions, the frozen water in
the material is converted directly from a solid
to a gas (sublimation) without passing through
a liquid phase. This leaves the material
dehydrated and in a stable, freeze-dried state.

3. TRIPLE POINT OF WATER

4. FREEZE DRYERS
• Freeze dryers are large-scale dehydro
freezing instruments that are commonly
used in industrial settings.
• They work by removing water from food
products through a process called
sublimation, where ice is directly
converted to vapour without going
through a liquid phase.

5. INSTRUMENTATION OF FREEZE DRYER
Freeze dryer chamber:
This is the main component of a
freeze dryer. It is a vacuum-sealed
container where the product to be
freeze-dried is placed. The chamber
is equipped with shelves or trays
that hold the product during the
drying process.
Vacuum pump:
A vacuum pump is used to create
and maintain a low-pressure
environment in the freeze dryer
chamber. This is essential for the
sublimation process to occur.
Condenser:
A condenser is used to trap the water
vapor that is removed from the product
during the freeze-drying process. The
water vapor is frozen onto the
condenser coils and removed from the
chamber, preventing it from re-
entering the product

6. Temperature sensors:
Temperature sensors are used to monitor the temperature of
the product and the freeze dryer chamber during the drying
process. This helps to ensure that the temperature is
maintained within a safe range and that the product is not
overheated.
Pressure sensors:
Pressure sensors are used to monitor the pressure within the
freeze dryer chamber. This helps to ensure that the vacuum
level is maintained at the appropriate level for the
sublimation process to occur.

7. Control system:
A control system is used to monitor
and control various aspects of the
freeze-drying process, such as
temperature, pressure, and vacuum
level. This helps to ensure that the
process is carried out accurately and
consistently.
Heating source:
A heating source, such as a heating
coil, is used to provide heat to the
product during the drying process.
This helps to speed up the sublimation
process and reduce the overall drying
time.
Overall, the freeze dryer instrumentation is a complex and precise system that requires careful
monitoring and control to ensure the quality of the final product.

8. WORKING
• Pretreatment
pre concentrate your product in normal dryer.
• Prefreezing
-18°C TO -50°C
• Primary drying
Application of vacuum reduce the boiling point of
water. 30°C/24hrs.
• Secondary drying
At 20°C
• Packaging
Vaccum or inert gas.

9. TYPES OF FREEZE DRYER
• Different types of dryer are used depending on the materials to be
dried.
• The dryers are classified as:-
1. Pilot freeze drying.
2. Industrial freeze drying
a. Multi batch freeze dryers
b. Continuous freeze dryers
c. Tunnel freeze dryers
d. Vacuum spray freeze dryers

10. PILOT FREEZE DRYERS
• Pilot freeze dryers mainly used
for food laboratories and
pharmaceutical industries.
• Since they are used to explore
possibilities for the preservation
of biological materials.

11. INDUSTRIAL FREEZE DRYERS
Multi batch freeze dryers:-
• Utilization of resources is minimum
in batch type dryers. So as to
increase the utilization of available
resources the multi batch freeze
dryers are introduced with number
of batch cabinets.

12. Continous freeze dryers
• The continuous type of dryers is
economic in terms of labours, large
capacity and to get uniform drying.
• Two types of continuous freeze dryers
are available:
• 1. Static or tray in which the freeze
dried products is stationary on trays.
• 2. Dynamic or trayless dryer, in which
product is moved with belt conveyors.

13. Tunnel freeze dryer
• A tunnel type freeze dryer consists of large
vacuum cabinet in which tray carrying trolleys
are loaded at one end.
• The end is discharging end where the dried
products are unloaded.
• Vacuum locks are fixed in each end of the dryer.
• Low pressure steam is used to heat the plates.
• In this type of dryers it is impossible to dry
different type of food materials at the same time.
• Cottage cheese and coffee are the best examples
for this method of drying.

14. Vacuum spray freeze dryers
• The product is sprayed from a single jet upward
or downward in a cylindrical tower of 3.7m
diameter by 5.5m height.
• The liquids solidify into small particles by
evaporative freezing.
• The whole plant operates under a vacuum of
about 67 Pa.
• Frozen particles obtained by spraying into a
vacuum are about 150mm in diameterand loose
about 15% of moisture in the initial evaporation.
• There is no sticking of the particles.

15. APPLICATIONS OF FREEZE DRYER IN
FOOD INDUSTRY
Coffee products
• The brewed coffee from ground beans
is pre concentrated by evaporation and
freeze dried immediately to prevent the
large ice crystal.
• Then heat is applied for sublimation
process and further drying. The
entrapped vapour is remixed into the
freeze dried coffee to enhance the
flavor.

16. Fruits and vegetables
• Most of the fruits and vegetable
are suitable for freeze drying
process.
• For example strawberries should
be sliced then loaded directly into
trays, and dried with a temperature
of 50°C. A drying time of 2hours
is possible.
•

17. Mushrooms
• Wide varieties of mushrooms are
preferred for freeze drying,
pigmented varieties tending to
shrink more.
• They should be peeled, sliced and
blanched before being loaded into
trays. With a platen temperature
of 82°C, a drying time of 3 hours
is possible.

18. Shrimp
• The pink varieties of shrimp are preferred to the
brown for freeze drying.
• After cooking for 3 min, the shrimp is placed in
the drying chamber in trays between platens.
Best results are obtained with the platens at
52°C, which gives a drying time of 10h.
• Higher drying temperatures give a product
which dries in 8 hours but rehydrates less well.
• The product quality is much lower at the higher
temperature.
• Precooked salmon steaks 13 mm thick dry in
about 9 hours with a temperature of 100°C.

19. Egg
• Liquid egg is mixed with
stabilizers to a thick cream.
• The mix is then filled into trays to
a depth of 10 mm and the product
temperature reduced to -25°C.
• The complete drying stage is of the
order of 9-10 hours and egg is left
in the trays in the form of a
crystalline porous cake.
• The egg is broken up and then
sieved to a powder and packed in
sacks.

20. WHY TO CHOOSE FREEZE DRIED
FOODS?

21. ADVANTAGES OF FREEZE DRYING
• Retain taste, smell and texture
• Fewer loss of nutrients
• Reduce weight
• Fewer preservative
• Extended shelf life
• Rapid rehydration advantage.

22. DISADVANTAGES OF FREEZE DRYING
• Expenses
• Storing
• Select food

23. DEHYDRATED Vs FREEZE DRIED
STRAWBERRY
TOMATO
MEAT

24. CONCLUSION
• The freeze drying process is
expensive, which restricts its
applicationon 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.

25. THANK YOU…
REFERENCE
• Akers MJ, Fites AL, Robinson RL.
Journal of freeze drying science and
technology.
• Rambhatla S, Pikal MJ. Heat and mass
transfer scale up issues during freeze
drying.
• Roy ML, Shah S. Importance of freeze
dried pharmaceuticals. SUBMITTED BY
Shivansh Suman
MSc. Food Technology
DSFT, BHU.