In the Carbon Dioxide Process of decaffeinating coffee, green coffee beans (milled but not yet roasted) are soaked in supercritical carbon dioxide (highly compressed carbon dioxide) at 73 to 300 atmospheres of pressure for about ten hours, which extracts the caffeine from the coffee beans.
Then the pressure is reduced and the CO2 either evaporates or goes through water (in the Sparkling Water Process) or activated carbon filters (in the Carbon Dioxide Process) to eliminate the caffeine. The CO2 is then used again.
This method removes anywhere from 95% to 99% of caffeine, meaning that most 12-oz cups of coffee end up with about 5mg of caffeine. The captured caffeine is sold to beverage and supplement companies for use in their products.
However, other chemical compounds within the coffee - many of which are beneficial to health - are also stripped in the process. This results in a coffee that's slightly less healthy than the origin, unaltered coffee, but is suitable for those with caffeine sensitivity or want to reduce their caffeine intake and help deal with withdrawal side effects. It also reduces the acidity of the coffee, resulting in a smoother tasting coffee.
Decaf Coffee Flavor
The removal of caffeine from coffee is not 100% exact, and many of the 1000 other chemical compounds in coffee are also affected, including some that affect taste. While decaffeinated coffee tastes better than no coffee, some people swear that there's a lack of flavor.
Another factor to consider is that decaf coffees are typically made using very mild coffees to begin with - Colombian, Mexican, Brazilian, Peru - which means that they're made from coffees that are smooth and mild rather than robust and interesting.
Our recommendation is to simply enjoy your decaf coffee if you're avoiding caffeine.
Supercritical Carbon Dioxide
The supercritical state of carbon dioxide is superior to water in this process because it has the desirable diffusive properties of a gas yet an increased density like a liquid.
An advantage of this decaffeination method is the avoidance of the use of potentially harmful chemical solvents. The Carbon Dioxide method is also called the Supercritical Fluid Extraction Process; Sparkling Water Process; and CO2/Water Process, with variations.
Decaffeinated Coffee and Espresso Tips
For tips on brewing the perfect cup of decaffeinated coffee see our section on coffee brewing. You can also read detailed coffee flavor profiles of gourmet coffee and instructions on preparing Espresso Drink Recipes.
For step-by-step instructions see Pulling A Perfect Espresso Shot as well as How to make Lattes and Cappuccinos.
For detailed definitions of coffee terminology see the Coffee and Espresso Glossary. Also check out the World's Best History of Coffee.
Is CO2 bad for you? isnt that putting bad oxygen back into your body?
No, the CO2 decaf isn't unhealthy, and there's no CO2 left in the coffee when it's roasted and brewed.