Are the chemicals used in decaffeinating coffee really safe? Are they related to cleaning fluid? Robert L. Wolke, professor emeritus of chemistry at the University of Pittsburgh, writes that the chemicals are related but different. (Caffeine itself belongs to the alkaloid family of powerful plant chemicals that includes nicotine, cocaine, morphine, and strychnine.)
Caffeine dissolves easily in many organic solvents such as benzene and chloroform, but they are not used, because they are toxic. The methylene chloride used in some decaffeinating processes is related to, but different from, the toxic perchlorethylene used in dry cleaning. Chemists have identified several hundred different chemicals in coffee, and removing the 1 or 2% of caffeine without ruining the flavor balance is difficult. Since the turn of the century, when a German chemist, Ludwig Roselius, studied the removal of caffeine from coffee, methylene chloride has been the solvent of choice. It dissolves other components minimally and vaporizes easily. Therefore, its remaining traces can be driven off by heat. However, in the 1980s, methylene chloride was denounced as a carcinogen. It is still used for decaffeinating, but the FDA limits its amount in finished product to 10 ppm. Industry sources indicate that the actual amount is less than 0.01 of that.
Caffeine is removed from green coffee beans before they are roasted. First, they are steamed, which brings most of the caffeine to the surface. Then, the caffeine is removed by washing with the solvent. To be called decaffeinated, coffee must have more than 97% of its caffeine removed.
An indirect method, sometimes called the water method, is often used. The caffeine, together with many desirable flavor and aroma components, is first extracted into hot water. (Caffeine dissolves in water; otherwise, we would not worry about its presence.) The caffeine is then removed from the water by an organic solvent, and the resulting caffeine-free water, with all of the original flavor components, is returned to the beans and dried onto them. The solvent never actually touches the beans.
An interesting, new practice is the use of ethyl acetate, an organic solvent, instead of methylene chloride. Because this chemical occurs in fruits and in coffee itself, it can be called, “natural.” The label of an ethyl-acetate-treated coffee may therefore claim that it is “naturally decaffeinated.” (The author points out that the same can be said for using cyanide, because it occurs “naturally” in peach pits.)
Much decaffeinated coffee today is made by a recently developed process that extracts the caffeine into harmless carbon dioxide that is in a form known to chemists as “supercritical.” It is neither gas, liquid, nor solid.
Finally, there is the ingenious “Swiss water process,” which washes the beans with hot water that is already full of all possible coffee chemicals except caffeine. Hence, there is no room for anything but caffeine to dissolve into it from the beans.