Commercial Floriculture

Freeze drying/Cryo drying

• It is a relatively new process.
  
• Fully opened flowers are cut into a uniform 15cm length and placed in vials so that the basal 5 cm are immersed in solutions of glycerine, clove oil, ethylene glycol, dimethyl sulfoxide and wetting agent.
  
• Various concentrations and combinations are used for stem uptake.
  
• After this pretreatment, flower-stems are re-cut to 5 cm in length and placed in a freezing temperature at – 800C for 12 hours.
  
• Then the flowers are immediately placed in a freeze dryer at 200C and under a vacuum of less than 100 microns for 7 days.

  Two phases in freeze dying
  1. Freezing phase.
  2. Vacuum drying phase.

Principle :
• Freeze drying is a dehydration process that causes vaporization of water directly from a solid ice crystal state to a vapour state without passing through normal liquid state.
• Flowers suited for freeze drying include carnation, Antirrhinum and roses.

Advantages :
• Texture, structure, shape, size, colour etc are similar to fresh ones.

Disadvantages :
• High cost of equipment
  
• Electrical energy consumption.
• Equipment maintenance cost is higher
  
• Requires precise processing techniques.
  
• Though expensive, freeze drying is becoming very popular in U.S. to preserve special occasion flowers. Brides often choose freeze drying to preserve their wedding bouquets.
  
• Vacuum drying temperature had more effect on rose and carnation flowers than freezing temperature. Lower vacuum drying temperature (27 0C) resulted in flower with colour closer to fresh and control flowers, while higher vacuum drying temperature (470C) resulted in lower moisture content and stronger/stiffer petals but more changes in colour.

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