Solvent Process

Technically speaking, all of the processes are solvent-based, since a solvent merely refers to a substance that is capable of dissolving another substance. However, in this field the common usage is to use the terms "solvent" or "chemical solvent" to refer to the process that uses either methylene chloride (dichloromethane) or ethyl acetate. There are two ways in which solvents are used to remove caffeine from coffee: a direct process, and an indirect process. The steps are essentially the same whether methylene chloride or ethyl acetate is used.

In the direct process, the beans first are steamed, which causes them to swell and become somewhat more permeable. The beans are then put into contact with the solvent, under pressure, for a specified period of time, which will, by and large, selectively extract the caffeine. The solvent is then processed to remove the caffeine, and can be reused for the next batch. The beans are usually steamed again after treatment in order to remove the remaining solvent.

In the indirect process, the beans are soaked in hot water, which removes almost all of the soluble compounds, including the caffeine. The water is drained off and mixed with the solvent, which bonds with the water. The solvent/caffeine mixture, less dense than the water, floats to the surface where it can be removed. The water and beans are mixed together, and the beans soak up most of the lost flavors.

Ethyl acetate is a substance that occurs naturally in many fruits and other foods, thereby earning the "natural" label, and it is is marketed towards those who are concerned that methylene chloride may have adverse health effects. Note that although ethyl acetate occurs in nature, the substance used for decaffeination likely has an industrial origin, thereby undercutting the "natural" appellation. The US Food and Drug Administration has labeled ethyl acetate as "Generally Recognized as Safe " (GRAS).

The dangers of methylene chloride decaffeination are widely debated: the World Health Organization found the main toxic effects of the chemical itself (without evaluating the decaffeination process) to be reversible central nervous system depression and carboxyhaemaglobin formation. Additional effects reported were liver and renal dysfunctions, hematological effects, and neurophysiological and neurobehavioral disturbances. The studies were not able to make definitive conclusions regarding any links between methylene chloride exposure and cardiovascular disease or cancer. (The WHO Environmental Health Criteria Series, volume 164.)

However, processing virtually eliminates any residual solvent content, and levels cannot exceed regulated levels. Methylene chloride evaporates at 104 degrees F (40 degrees C), and so would not survive the roasting process.Though the chemical itself may be dangerous, there do not appear to be any tests that found residual methylene chloride in decaffeinated coffee, and it is also GRAS for this purpose.