"The third approach, supercritical carbon dioxide decaffeination, is very similar to the direct solvent methods, except that in this case the solvent is carbon dioxide. High-pressure vessels (operating at roughly 250 to 300 times atmospheric pressure) are employed to circulate the carbon dioxide through a bed of premoistened, green coffee beans. At such pressures, carbon dioxide takes on unique, 'supercritical' properties that enhance its usefulness as a solvent. Supercritical carbon dioxide has a density like that of a liquid, but its viscosity and diffusivity are similar to those of a gas. These attributes significantly lower its pumping costs. Carbon dioxide is a popular solvent because it has a relatively low pressure critical point, and it is naturally abundant. The caffeine-rich carbon dioxide exiting the extraction vessel is either channeled through a bed of activated charcoal or through a water 'bath' tower to absorb the caffeine. The carbon dioxide is then recirculated back to the extraction vessel. Supercritical carbon dioxide decaffeination is capital-cost intensive, but it offers very good yields. It typically can extract 96 to 98 percent of the caffeine originally present in the beans."