Organic solvent extraction
During the 1970s, dichloromethane was used due to its low toxicity. It is able to dissolve caffeine without dissolving sugars, peptides and other important flavour constituents in the beans. It was later found to be carcinogenic and its use was reduced.
The coffee beans are steamed in a rotating drum for 30 minutes. They are then rinsed for 10 hours using dichloromethane removing the caffeine. The caffeine saturates the solvent and is removed. The solvent is evaporated when the beans are steamed for a second time and then vacuum dried. Little solvent residue remains in the beans.
The second method is sometimes called the “water process” method. The green beans are placed in the water and heated to around boiling point, so that the caffeine is removed. The other flavours are also removed. The mixture is treated with solvent and the caffeine is absorbed and evaporated. The beans are placed in to contact with the mixture again so that the beans can gain the flavour they lost in the earlier process.
Ethylene acetate was introduced in the 1980s and early 1990s in replace of dichloromethane. It is moderately toxic, but due to its presence in fruits, is sometimes branded safe.
“The United States Food and Drug Administration (FDA) has authorized by regulation the use of both methylene chloride and ethyl acetate for coffee decaffeination. According to an FDA report in the Federal Register, most decaffeinated coffee has less than 0.1 parts per million (ppm) of residual methylene chloride, 100 times less than the maximum level of 10 ppm allowed by the FDA.”3