Coffee beans are first soaked in water to extract caffeine. Next, the beans are removed and methylene chloride is added to bond with the caffeine. The methylene chloride/caffeine mixture is removed by skimming it out of the liquid.
The beans are then placed back in the remaining caffeine-free water to reabsorb the decaffeinated liquid.
Methylene chloride can remain in small quantities in the decaffeinated beans, however, it evaporates at 40°C and cannot survive the roasting and brewing process.