Coffee beans can be decaffeinated by two methods. The water process and the solvent process.
In the “water process” green beans are soaked in hot water for 10 minutes to 2 hours. In addition to leeching out most of the caffeine, this process removes most of the compounds that give coffee its flavour. Manufactures then have to return as much of the lost flavour compounds as possible. After soaking, the caffeine-laced water is drawn off and the caffeine is removed. There are two ways to do this.
The water is mixed with a caffeine-specific solvent such as methylene chloride or ethyl acetate.
WHAT IS METHYLENE CHLORIDE?
Methylene chloride is a highly volatile result of industrial emissions. It can be used as a paint stripper, degreaser, aerosol spray propellant and a blowing agent for polyurethane foams. It is metabolized by the body to carbon monoxide and can potentially lead to carbon monoxide poisoning. Prolonged skin contact can result in dissolving of some of the fatty tissues in skin, resulting in skin irritation or chemical burns. Acute exposure by inhalation has resulted in optic neuropathy and hepatitis. It has been linked to cancer of the lungs, liver and pancreas in laboratory animals. It also crosses the placenta. Fetal toxicity in women who are exposed to it during pregnancy, however, has not been proven. In animal experiments, it was fetal toxic.
WHAT IS ETHYL ACETATE?
Ethyl acetate is a flammable colourless liquid with a fruity odour. It is used as a solvent for varnishes, lacquers, dry cleaning, stains, fats and nitrocellulose. It is released during the production of artificial silk and leather, and during the preparation of photographic films and plates. It is released during the manufacture of linoleum, and “plastic” wood, dyes, pharmaceuticals, drug intermediates, acetic acid, artificial fruit flavourings and essences, and perfumes and fragrances. Ethyl acetate is used as a solvent in nail polish remover, base coats and other manicuring products. Short term exposure to high levels of ethyl acetate results first in irritation of the eyes, nose and throat, followed by headache, nausea, vomiting, sleepiness and unconsciousness. Very high concentrations may cause stupor. Prolonged exposure may cause damage to the lungs and heart, and kidney and liver problems.
The caffeinated water can also pass over acid-treated carbon filters to which the caffeine binds. The liquid is then returned to the beans, which reabsorb some of the favour compounds (and the chemicals in the water). After this step, the beans are dried and shipped to roasters.
So called solvent processing is more direct. The green coffee beans are washed with a caffeine solvent (again either methylene chloride or ethyl acetate) in tubs or rotating drums. The caffeine is then filtered from the liquid solvent. Because this process is relatively fast more of the flavour compounds are usually retained.
After the caffeine-laden solvent is removed, the beans are processed with steam to remove most (but not all) of the residual solvent. In 1985 the Food and Drug administration ruled that there was no risk in drinking solvent-processed decaffeinated coffee.