The Carbon Dioxide Method, also known as the Supercritical CO2 Method, is another all-natural method of decaffeination. It was first developed in 1967 by Kurt Zosel, a scientist at the Max Planck Institute for Coal Research. Zosel worked with supercritical C02. What’s Supercritical C02? It’s what happens when C02 is heated to at least 86°F a pressure of 73.8 bar. The C02 then goes “supercritical” and has a host of scientific uses.

One way supercritical C02 is used is to separate a specific substance from a mixture. Zosel realized that this process could be applied to the caffeine in coffee beans, and by 1970 he had obtained a patent for his method.

In the C02 Method, beans are first soaked in water, causing them to swell. The beans are then sealed in a chamber with C02 that is brought to a pressure of 1,000 pounds per square inch, and a temperature of almost 200°F. 

This supercritical C02 then acts as solvent, pulling the caffeine from the coffee beans. This takes about 5 to 7 hours to complete. The leftover C02 can then be recaptured and reused, helping to make this a sustainable method.

The C02 Method has also been acclaimed for not disrupting the flavor compounds of coffee beans. Unlike the Swiss Water Process, where compounds are removed from and then reintroduced back into beans, The C02 Method only extracts caffeine. In fact, some taste tests have been quite laudatory of C02 processed decafs.

So what’s the drawback to the C02 Method? It’s very expensive. The cost of running a lab that can produce supercritical C02 decaf is quite high, and the process itself is demanding. Because of this, the process has largely been used to decaffeinated commercial grade, and not specialty grade, coffee.

The process is beginning to make itself known in specialty decaf circles, however. Currently, there is a C02 decaffeination plant in Germany producing certified-organic coffee called CR3. The plant in  fact has pioneered their own innovation to the method, called the Subcritical Method. Using this method, the plant is able to extract caffeine at a lower temperature and a lower pressure, which they say helps preserve the coffee’s flavor.

Whether the C02 Process will grow to the same ubiquity as the Ethyl-Acetate or Swiss Water Process remains to be seen, but it is certainly a method to keep your eye on.