The decaffeination method starts with green coffee beans — seeds of coffee cherries that have been separated from their fruit and dried, but not yet roasted. Legend goes that decaf coffee was discovered when coffee beans fell overboard from a ship and became less caffeinated by the salt water soak. From there, the first patented decaffeination methods used a chemical solvent like ammonia and benzene.
Thankfully neither of those methods are still used, but the idea of soaking green coffee beans in a fluid that can extract the caffeine content, while — by the end of the process — leaving the rest of the flavor compounds in place, is basically how it still works.
When digging further into decaf, you’ll find terms such as the Swiss Water process, EA, and CO2, all of which can produce tasty decaf.
The Swiss Water process, performed in a specific plant in British Columbia, involves Green Coffee Extract, which contains all of the compounds found in coffee except for caffeine. Caffeine from the coffee soaked in this solution travels out into the liquid, where it can then be filtered out using a carbon filter.
In the Ethyl Acetate process (also called sugar cane process, because the chemical involved is derived from Colombian sugarcane), green coffee is steamed and then soaked in an Ethyl Acetate-rich solution which extracts caffeine, but leaves most other compounds intact.
The CO2 process uses a different kind of fluid, carbon dioxide pressurized at above 250 times atmospheric pressure. At that high pressure, CO2 is another excellent solvent for caffeine, which can then easily be filtered out using activated carbon.
Decaffeination involves the breakdown of the structure of a coffee bean in a way that will affect its flavor when it’s roasted. It might also affect its appearance, as the breakdown of cell walls in decaffeination can make it easier for oils to escape the beans even in medium roasts (while, in caffeinated coffee, oils are something we don’t usually see unless it’s dark roast coffee). Finally, while caffeine isn’t the main compound that makes coffee bitter, it does contribute to that flavor, so its removal can actually reduce bitterness.
Overall, if you take beans from one farm and decaffeinate some while leaving the rest, you’d likely be able to taste a difference. That said,improvements in decaffeination in the last decades have made the difference much smaller. In turn, because the decaf processes themselves have improved, exporters, importers, and roasters are more comfortable using higher quality coffee for their decafs and have gotten better at roasting them. We’ve certainly tasted many decafs that, without knowing it, we would have never been able to identify as lacking caffeine.
While no decaffeination processes offer a 100 percent caffeine-free product, most decaf coffee has a negligible amount of caffeine. Swiss Water’s website promises 99.9 percent caffeine reduction, while studies of other methods commonly used in specialty found results close to 97 percent. It’s likely that decaffeinated coffee won’t give you any sort of caffeine buzz, but for those with extreme intolerance to caffeine consumption, it might still be wise to ingest decaffeinated coffee with caution.