This
is the first choice for aroma extraction, decaffeination, defatting, pesticide
removal, phytoextraction, and sterilization. It has become an important
commercial and industrial method to extract chemicals due to its low toxicity
and environmental impact.
The
process uses a relatively low temperature and with the stability of CO2 it
allows for compounds that are extracted from plant sources like essential oils
to encounter limited damage or chemical
denaturing.
Supercritical CO2 is the fluid state of carbon dioxide
and it is temperature and pressure is held at or above its critical stage. When
this happens CO2 can adopt properties midway between a gas and a liquid. It
begins to behave as a supercritical fluid, expanding to fill a container like a
gas but with a density that of a fluid.
Supercritical fluid is where distinct liquid and gas
phases are non-existent. It causes
molecules to go through solids like a gas and dissolve materials like a
liquid. Small changes in pressure and
temperature when close to its critical point – where phases in boundaries do
not exist it will allow for many properties to be re-fined within that
extracted material.
The common solvents used in this method of extraction
instead of chemical solvents are CO2 and water as supercritical fluids.
The cost can be prohibitive however the yield of the
essential oils is superior in quality and sterilization.
http://en.wikipedia.org/wiki/Supercritical_carbon_dioxide
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