The direct solvent method is the oldest and most common decaffeination process. On coffee signs and bags it is typically not identified at all, or called by various euphemisms like European or traditional process. The beans are first steamed to open their pores, then soaked in an organic solvent that selectively unites with the caffeine. The beans are then steamed again to remove the solvent residues, dried, and roasted like any other green coffee.
A more recently developed process called the indirect solvent method starts by soaking green beans in near-boiling water for several hours. The water is transferred to another tank, where it is combined with a solvent that selectively absorbs most of the caffeine. The caffeine-laden solvent is then skimmed from the water, with which it has never really mixed. The water, now free of both caffeine and solvent, still contains oils and other materials important to flavor. In order to return these substances to the beans, the water is returned to the first tank, where the beans reabsorb the flavor-bearing substances from the water.
What About the Solvents? The joker in the process is still the solvent. People concerned about the effects of coffee on their health obviously are not going to feel comfortable purchasing a product containing even minute traces of solvent. In 1975 one of the most widely used solvents, trichloroethylene, was named a probable cause of cancer in a "Cancer Alert" issued in 1975 by the National Cancer Institute.
Also, no one knows how much of the solvent residue — if any — is retained in the brewing process and ends up in the cup. Given the volatility of the solvent and the relatively minuscule amount left in the bean after roasting, it is most likely that none whatsoever ends up in the coffee we ultimately consume.
A New and Better Solvent: Methylene Chloride. Nevertheless, the news that the caffeine that some feared caused heart disease was being replaced by a solvent that actually did cause cancer provoked understandable consternation among health-conscious consumers.
The coffee industry promptly responded by replacing trichloroethylene with methylene chloride, a solvent not implicated in the National Cancer Institute study. So far tests of methylene chloride have not linked it to any known disease, and given its volatility (it vaporizes at 104° F; coffee is roasted at over 400° F for at least 15 minutes, then brewed at 200° F) it seems hardly possible that any of the 1 part per million occasionally found in the green beans could end up in the consumer’s cup or stomach.
An Even Newer and Better Solvent. A second solvent is now in use in some European decaffeination plants: ethyl acetate. Like methylene chloride, ethyl acetate has not been implicated in any diseases, and environmentalists consider it more benign than methylene chloride. Because ethyl acetate is derived from fruit, some publicists and brochure writers have taken to calling coffees decaffeinated using ethyl acetate "naturally decaffeinated," and you may see them so advertised.