How is coffee decaffeinated?

Decaffeination happens before roasting, while the beans are still green. In solvent methods, beans are steamed or soaked and then rinsed with ethyl acetate or methylene chloride, which bind to caffeine; the solvents are removed and roasting drives off remaining traces. The Swiss Water Process uses only water: flavour-saturated water pulls caffeine out, and carbon filters trap it. The CO2 method uses carbon dioxide under high pressure, which selectively dissolves caffeine. Decaf is not completely caffeine-free, but must typically have at least 97 percent of the caffeine removed.