Caffeine occurs naturally in coffee. There are four common ways to remove it, all of which occur before the beans are roasted, says Chris M. Hallien, the director of coffee for Intelligentsia.
In the direct method, a solvent that bonds to caffeine molecules is applied directly to green coffee beans that have been softened with steam. The beans are then rinsed to wash away the solvent and the caffeine. The most widely used solvents for this process are methylene chloride and ethyl acetate. According to OSHA’s website, methylene chloride (a.k.a. dichloromethane) “is used in various industrial processes, in many different industries including paint stripping, pharmaceutical manufacturing, paint remover manufacturing, and metal cleaning and degreasing.” Mark Howell, the director of laboratory operations for Coffee Solutions, says that the FDA requires coffee decaffeinated using methylene chloride to have less than 10 ppm (parts per million) of residue, and that “coffee produced [using] this method contains around 2 or 3 ppm before roasting and less than 0.1 ppm after roasting.” Ethyl acetate is a chemical that occurs naturally in many fruits, so Howell says that coffee processed with it is referred to as “naturally decaffeinated.”
The indirect method also uses methylene chloride and ethyl acetate to remove caffeine, but the beans are first soaked in water to extract their caffeine (which is water soluble). Then the beans are removed, and the water is treated with a solvent to remove the caffeine. Because many flavor compounds and oils are also extracted from the beans during soaking, Howell says, the treated water is reintroduced to the beans so they can reabsorb the compounds.
Water-processed decaffeination is similar to the indirect method. Water processing differs in that the water is run through a carbon filter to remove the caffeine instead of being treated with a solvent. As in the indirect process, Howell says, the treated water goes back on the beans so they can reabsorb extracted flavor compounds.
Finally, in the supercritical process, steamed beans are placed in a container under high pressure along with liquid carbon dioxide or liquid oxygen, which act as solvents, attracting the caffeine molecules. As the container’s pressure drops, Intelligentsia’s Hallien says, the carbon dioxide or oxygen changes from liquid to gas and evaporates, taking the caffeine with it. Howell says that because flavor molecules are larger than caffeine molecules, they remain intact, resulting in better-tasting decaf coffee than the stuff produced using the indirect or water-processing methods.
There are no requirements for labeling decaf methods, Howell says, so there’s no way to tell which process has been used on your coffee. “But you should assume it’s methylene chloride–processed unless it says otherwise,” he says. In terms of flavor, he thinks methylene chloride produces the best, but says that decaf “can’t be as good as the original, no matter which process you use.”