Editing Instant coffee (section)

===Freeze drying===
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[[Image:Production freeze dryer.JPG|thumb|right|A [[freeze drying|freeze dryer]]]]

The basic principle of [[freeze drying]] is the removal of water by [[sublimation (chemistry)|sublimation]].

Since the mass production of instant coffee began in post-WWII America, freeze-drying has grown in popularity to become a common method. Although it is more expensive, it generally results in a higher-quality product.

# The coffee extract is rapidly frozen and is broken into small granules. (Slower freezing would lead to larger ice crystals and a porous product; it can also affect the colour of the coffee granules).
# The granules are sifted and sorted on size.<ref name="MussattoMachado2011"/>
# Frozen coffee granules are placed in the drying chamber, often on metal trays.
# A vacuum is created within the chamber. The strength of the vacuum is critical in the speed of the drying and therefore the quality of the product. Care must be taken to produce a vacuum of suitable strength.
# The drying chamber is warmed, most commonly by [[thermal radiation|radiation]], but [[heat conduction|conduction]] is used in some plants and [[convection]] has been proposed in some small pilot plants. A possible problem with convection is uneven drying rates within the chamber, which would give an inferior product.
# Sublimation—the previously frozen water in the coffee granules expands to ten times its previous volume. The removal of this water vapor from the chamber is vitally important, making the condenser the most critical and expensive component in a freeze-drying plant.
# The freeze-dried granules are removed from the chamber and packaged.