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      • Cryogenics
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    • Brands
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      • Busch
      • CTI Cryogenics
      • Ecodyst
      • Edwards
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      • Fisher scientific
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      • Henniker Plasma
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  • Home
  • Applications
    • Vacuum chambers
    • Vacuum gauges
    • Vacuum pumps
    • Freeze drying
    • Cryogenics
    • Thin film deposition
  • Brands
    • Becker
    • Briskheat
    • Busch
    • CTI Cryogenics
    • Ecodyst
    • Edwards
    • Elmo Rietschle
    • Fisher scientific
    • Gamma Vacuum
    • Henniker Plasma
    • Hexisense
    • Inert Glove Box
    • Inficon
    • Kinney
    • KNF
    • Leybold
    • MDC Vacuum
    • Picosun
    • Prevac
    • Plasmionique
    • Precision Plus
    • Sairem plasma
    • Stokes
    • Stensborg Lithography
    • Torr Scientific
    • ThetaMetrisis
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    • Vacgen VG
    • Vacuubrand
    • Varian vacuum
    • VPI Technology
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    • Adixen - servicing
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Australian vacuum first choice for freeze drying

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Freeze DRYING

Freeze drying process advice and help in Australia.
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Process

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Freeze drying, also known as lyophilisation or cryodesiccation, is a low temperature dehydration process  that involves freezing the product, lowering pressure, then removing the ice by sublimation. This is in contrast to dehydration by most conventional methods that evaporate water using heat.

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), food  processing (e.g., coffee) and preservation.

Stages of freeze drying

There are four stages in the complete freeze drying process: pretreatment, freezing, primary drying, and secondary drying. 

Pretreatment

Pretreatment includes any method of treating the product prior to freezing. This may include concentrating the product, formulation revision (i.e., addition of components to increase stability, preserve  appearance, and/or improve processing), decreasing a high-vapor-pressure solvent, or increasing the surface area. Food pieces are often IQF treated to make them free flowing prior to freeze drying. In many  instances the decision to pretreat a product is based on theoretical  knowledge of freeze-drying and its requirements, or is demanded by cycle  time or product quality considerations.

Freezing and annealing

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 form a network within the product  which promotes faster removal of water vapor during sublimation. To produce larger crystals, the product should be frozen slowly or can  be cycled up and down in temperature in a process called annealing.  The freezing phase is the most critical in the whole freeze-drying  process, as the freezing method can impact the speed of reconstitution,  duration of freeze-drying cycle, product stability, and appropriate  crystallization.

Primary drying

During the primary drying phase, the pressure is lowered (to the range of a few millibars), and enough heat is supplied to the material for the ice to sublime. The amount of heat necessary can be calculated using the sublimating molecules' latent heat of sublimation.  In this initial drying phase, about 95% of the water in the material is  sublimated. This phase may be slow (can be several days in the  industry), because, if too much heat is added, the material's structure  could be altered. 

In this phase, pressure is controlled through the application of partial vacuum.  The vacuum speeds up the sublimation, making it useful as a deliberate  drying process. Furthermore, a cold condenser chamber and/or condenser  plates provide a surface(s) for the water vapour to re-liquify and  solidify on. It is important to note that, in this range of pressure, the heat  is brought mainly by conduction or radiation; the convection effect is  negligible, due to the low air density. 

Secondary drying

The secondary drying phase aims to remove unfrozen water molecules, since the ice was removed in the primary drying phase. This part of the freeze-drying process is governed by the material's adsorption isotherms.  In this phase, the temperature is raised higher than in the primary  drying phase, and can even be above 0 °C (32 °F), to break any  physico-chemical interactions that have formed between the water molecules and the frozen material. Usually the pressure is also lowered in this  stage to encourage desorption (typically in the range of microbars, or  fractions of a pascal). However, there are products that benefit from increased pressure as well. After the freeze-drying process is complete, the vacuum is  usually broken with an inert gas, such as nitrogen, before the material  is sealed. At the end of the operation, the final residual water content in the product is extremely low, around 1% to 4%. 

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  • Home
  • Vacuum chambers
  • Vacuum gauges
  • Vacuum pumps
  • Freeze drying
  • Cryogenics
  • Thin film deposition
  • Becker
  • Briskheat
  • Busch
  • CTI Cryogenics
  • Ecodyst
  • Edwards
  • Elmo Rietschle
  • Fisher scientific
  • Gamma Vacuum
  • Henniker Plasma
  • Hexisense
  • Inert Glove Box
  • Inficon
  • Kinney
  • KNF
  • Leybold
  • MDC Vacuum
  • Picosun
  • Prevac
  • Plasmionique
  • Precision Plus
  • Sairem plasma
  • Stokes
  • Stensborg Lithography
  • Torr Scientific
  • ThetaMetrisis
  • Ulvac vacuum
  • Vacgen VG
  • Vacuubrand
  • Varian vacuum
  • VPI Technology
  • Welch vacuum
  • Adixen - servicing
  • Alcatel - servicing
  • Pfeiffer - servicing
  • Calibration
  • Consultants
  • Vacuum training
  • Pump repairs
  • Refurbished pumps
  • Contact Us
  • Links and Social
  • Testimonials-Corporate

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