Freeze DryingNew preservation technology

TD 611

Also known as lyophilisation,

lyophilization, or cryodesiccation

“lyophilization” – process for a product

that “loves the dry state”

Dehydration process

Typically used to preserve a

perishable material or make the

material more convenient for transport

Frozen water is sublimated to vapor

phase

Freeze Drying

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Nearly every food can be freeze -dried

Astronauts’ and hikers’ food

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Phase Diagram of water

Pre

ssu

re

Temperature

Vapor Pressure

(mbar)

Temperature

(C)

6.104 0

2.599 -10

1.034 -20

0.381 -30

0.129 -40

0.036 -50

0.011 -60

0.0025 -70

0.0005 -80

Pressure-Temperature for sublimation

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Food is pre-treated, flash frozen &Placed in a vacuum chamber

About 90% of the food’s moisture is drawn off by evaporating the ice of temperatures as low as -50 C

Water replaced, Original flavor, aroma, texture, and appearance

Freeze – dried food sealed in moisture + Oxygen proof packaging to ensure freshness

I

II

IIIIV

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Compressor

Door

Heated shelves Refrigeration coils Cooling coils

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• Method of treating the product prior to freezing Eg. Conc. the product, formulation revision

Pre-treatment

• Cool the material below its triple point (Complex process)• Larger crystals are easier to freeze-dry, so slow cooling good (in certain materials)

Freezing

• Lowering of Pressure (to the range of a few millibars)• Sublimation by supplying heat• Re-solidification of moisture on Condenser

Primary Drying

• Temp. raised to break physico-chemical interactions remove unfrozen water• Pressure is also lowered in this stage to encourage desorption• Vacuum is usually broken with an inert gas

Secondary Drying

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Vacuum Pump

Condenser Plate

Heat

ing

Plat

es

Heating P

lates

Moving

Sublimation

front

Frozen vapors

PRODUCT

Frozen

Dried

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Pressure -Temp variation during the processMoving Sublimation front

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Industrial freeze dryers

Home freeze dryers

Cost of a small home freeze dryer ~ 4-5 lakhs INR

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Heat Transfer

Driving Potential - temp. difference

𝑞 =−𝐾𝐴

∆𝑥(𝑇𝑠𝑢𝑏−𝑇𝑓)

Mass Transfer

Driving Potential - Pressure difference

𝑚 =𝑘𝑑𝐴

∆𝑥(𝑃𝑠𝑢𝑏−𝑃𝑐𝑜𝑛𝑑) = 𝜌𝐴

𝑑 (∆𝑥)

𝑑𝑡

Coupling of heat and mass transfer

𝑞 = 𝑚 𝐿

** Valid under suitable assumptions

𝑃𝑐𝑜𝑛𝑑 = 𝑃𝑠𝑢𝑏 +𝑘

𝑘𝑑𝐿(𝑇𝑓 − 𝑇𝑠𝑢𝑏

Frozen Layer

Dried Layer

Plate heater

L

∆𝑥

Tsub, Psub

Tf, Pcond

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Preservation of temperature sensitive productsBiological origin materials, eg. Blood plasma, enzymes, vaccines etc.

Health friendly

No preservatives, GMO free, Gluten free, Vegetarian and vegan

Almost all food products can be freeze-dried

Fruits, vegetables, meat, pharmaceuticals, ice-cream, sandwich… anything

High Stability (for several years)

Once packed properly, long shelf life at ambient conditions for years

Preserves the natural color, taste and appearance

No damage to the natural properties of the product

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