How decaffeination works
There are three key methods for removing caffeine from regular coffee beans: The most common uses a chemical solvent, another uses liquid carbon dioxide (CO2), and the last simply uses water.
All take green, unroasted coffee beans, soak or steam them until the caffeine is dissolved or their pores are opened, and then extract the caffeine.
While the CO2 and water methods are considered chemical-free, the solvent method relies on synthetic chemicals such as ethyl acetate (naturally found in some fruits) and methylene chloride (commonly used in industrial applications such as in adhesives, paints, and pharmaceuticals).
The Swiss Water Process tends to produce the most flavorful coffee, Ristenpart says, because it’s good at removing caffeine and without stripping other flavorful compounds from the beans. But it’s also more expensive and difficult to produce at scale. For this reason, Ristenpart says, you’ll typically find it used on higher-end coffees, such as Blue Bottle.
None of these methods scrubs the bean of caffeine completely. While the Food and Drug Administration requires that at least 97% of caffeine be removed, some decaffeinated coffees can still contain between 3 and 12 mg of caffeine per cup.