Decaf coffee is composed of at least 3% of caffeine. Therefore, it is not absolutely caffeine free. Consequently, since it still contains caffeine, researches have discovered that consuming 5-10 cups of decaffeinated coffee is equivalent to drinking 1-2 cups of caffeinated coffee. Additionally, some of the adverse effects of drinking unfiltered coffee can also appear in the decaf ones. Probably because it still contains caffeine and other substances that cannot be removed by decaffeination. Or it can be the other way around, when important substances that are beneficial to the body are removed during the decaffeination process.
But how is coffee decaffeinated in the first place? A process called water decaffeinating removes the caffeine by soaking the beans in water before roasting it. Another method is steaming the coffee beans to dissolve the caffeine. As it rises to the surface, an organic solvent called methylene chloride is added to wash it off. But not all methods and processes are purely organic. There are methods that use chemicals like the solvent formaldehyde to absorb and get rid of caffeine in the coffee.