Ask the Experts; October 2002; Scientific American Magazine; by Staff Editor; 1 Page(s)
Fergus M. Clydesdale, head of the food science department at the University of Massachusetts at Amherst, provides this answer: There are currently three main processes, all of which begin with moistening the green or roasted beans to make the caffeine soluble. Decaffeination is typically carried out at 70 to 100 degrees Celsius.
In the first method, called water processing, the moistened coffee beans are soaked in a mixture of water and green-coffee extract that has previously been caffeine-reduced. Osmosis draws the caffeine from the highly caffeine-concentrated beans into the less caffeine-concentrated solution. Afterward, the decaffeinated beans are rinsed and dried. The extracted caffeinerich solution is passed through a bed of charcoal that has been pretreated with a carbohydrate. The carbohydrate blocks sites in the charcoal that would otherwise absorb sugars and additional compounds that contribute to the coffee's flavor but permits the absorption of caffeine. The caffeine-reduced solution, which still contains compounds that augment the taste and aroma, can then be infused into the beans. The water process is natural, in that it does not employ any harmful chemicals, but it is not very specific for caffeine, extracting some noncaffeine solids and reducing flavor. It eliminates 94 to 96 percent of the caffeine.