When carbon dioxide gas is cooled and placed under pressure, it becomes a liquid. In this state it is able to bind with the caffeine molecule in green beans as the carbon dioxide acts as a magnet. Green coffee is soaked in containers of liquid carbon dioxide until the caffeine is “soaked out”.
The carbohydrates and proteins in the coffee bean are not affected and they attribute to the flavour and smell after roasting. Purity of the coffee is assured because of the extremely low boiling point of carbon dioxide. The CO2 can now be recycled and used in other commercial products.