Freeze dryers work by first freezing the material and then using sublimation to turn frozen water directly into a gas. The key parts are drying chambers, heating coils, a vapor condensing system, and a vacuum pump. Freeze drying preserves the quality, shape, and rehydration properties of materials like foods and biological samples since it occurs below the freezing point and does not require melting. Its applications include heat-sensitive materials like foods, pharmaceuticals, and biological cultures.

1. Freeze Dryer

2. Freeze Dryer
Principal:
Freeze Dryer works on the principle of sublimation process.
Construction and Working:
 Freeze Dryer is also known as Lyophilization.
 Freeze drying or lyophilization is a drying method
where the solvent is frozen prior to drying and is
then sublimed, i.e., passed to the gas phase directly
from the solid phase, below the melting point of the
solvent.

4. The main parts of freeze dryer are:
 Drying chamber in trays.
 Heating coils.
 Vapor condensing or adsorption system with
refrigerator.
 Vacuum pump.

5.  During the freezing stage, the material is cooled below
its triple point, the lowest temperature at which the
solid, liquid and gas phases of the material can coexist.
 This ensures that sublimation rather than melting will
occur in the following steps. To facilitate faster and
more efficient freeze drying, larger ice crystals are
preferable. The large ice crystals forms a network
within the product which promotes faster removal of
water vapor during sublimation.

6. Triple Point
 In thermodynamics, the triple point of a substance is
the temperature and pressure at which the
three phases (gas, liquid, and solid) of that substance
coexist in thermodynamic equilibrium.
 For example, the triple point of mercury occurs at a
temperature of −38.83440 °C and a pressure of
0.2 mPa.(Megapascal).

7.  Sublimation is a process in which a solid turns directly
into gas without passing into liquid state.
 It works on the principle that solids have a weak
intermolecular force hence a higher vapour pressure
which converts it into directly vapour state.
 The sublimation step removes the water molecules that
were separated from the solids as ice crystals in the
freezing step.

8. Sublimation is the process by which solid
water is directly transformed into vapors water.
 Sublimation occurs when molecules of a solid
move fast enough to overcome the attractions
from other molecules and become a gas.

9.  Freeze drying results in a high quality product because
of the low temperature used in processing. The original
shape of the product is maintained and quality of the
rehydrated product is excellent.
 Primary applications of freeze drying include biological
(e.g. bacteria and yeasts), biomedical (e.g. surgical
transplants), and food processing (e.g. coffee)
and preservation.

10.  Freeze-drying is viewed as the optimal method of choice
for dehydration because of :
 The preservation of quality, meaning characteristics of
the food product such as aroma, rehydration, and
bioactivity, are noticeably higher compared to foods
dried using other techniques.

11. Advantages :
• Suitable for thermo-labile material.
• Loss of volatile is less.
• No migration occurs.
• Suitable for moisture sensitive material.
• Sterility maintain
Disadvantages:
• High costs.
• Time consuming.
• Oxidation may occurs.

12. Applications:
For production of dosage forms as injections,
solutions, suspensions.
For drying of Blood plasma and its fractionated
products, Bacterial & viral cultures, Human
tissue, Antibiotics, Steroids and food products.

13. So, It is increasingly applied to dry foods,
beyond its already classical pharmaceutical or
medical applications.
It keeps biological properties of proteins, and
retains vitamins and bioactive compounds.