How can compressed carbon dioxide remove caffeine from coffee beans?

Decaffeination removes much of the caffeine from coffee beans before roasting. One method uses carbon dioxide under conditions above its critical temperature and pressure, where it forms a supercritical fluid rather than separate ordinary liquid and gas phases.

Moistening the beans helps caffeine move from their interior. Dense carbon dioxide passes through them and dissolves caffeine selectively enough to make extraction practical. Solubility and movement through the beans depend on the process conditions.

The caffeine-containing fluid then enters a separation stage, where caffeine is removed, for example using an adsorbent. Carbon dioxide can be recovered and circulated again. The beans are subsequently dried and prepared for further processing.

The fluid acts as a carrier, not as a substance that destroys caffeine molecules. The challenge is removing caffeine while retaining desirable bean components and managing energy use. Other decaffeination processes use different solvents or water, so this route does not describe every decaffeinated coffee.