Why doesn't liquid CO2 decaffinate coffee and super critical CO2 does?
Liquid CO2 is not effective at decaffeinating coffee because it lacks the necessary solubility and selective properties. To understand why supercritical CO2 is used instead, we need to look at the fundamental principles of extraction.
Decaffeination is essentially the removal of caffeine from coffee while retaining its flavor compounds. Caffeine is a naturally occurring alkaloid, and its solubility depends on the solvent used. Regular liquid CO2 does not have the required solubility to extract caffeine effectively from coffee beans.
On the other hand, supercritical CO2 (carbon dioxide in a state between a gas and a liquid) is widely used in decaffeination processes because it can achieve the conditions necessary for successful extraction. The supercritical state enables CO2 to have increased solvency, similar to liquid solvents, while also exhibiting gas-like diffusivity, allowing it to permeate coffee beans easily.
The process involves exposing coffee beans to supercritical CO2, which acts as a solvent. Under high pressure and temperature, CO2 dissolves the caffeine, essentially forming a coffee extract with the caffeine suspended in it. The caffeine-rich CO2 is then separated from the coffee extract through pressure reduction, which returns CO2 to its gaseous state, leaving the decaffeinated coffee beans behind.
In summary, the difference in effectiveness between liquid CO2 and supercritical CO2 lies in their solubility and selective properties. Supercritical CO2 is more soluble and can better extract caffeine from coffee, making it the preferred method for decaffeination.