The Swiss Water Process uses Green Coffee Extract (GCE) for the caffeine extraction mechanism. Green Coffee Extract is a solution containing the water-soluble components of green coffee except for the caffeine.
The process relies on the stability of the soluble components of the GCE and the gradient pressure difference between the GCE (which is caffeine lean) and the green coffee (which is caffeine-rich). This gradient pressure causes the caffeine molecules to migrate from the green coffee into the GCE. Because GCE is saturated with the other water-soluble components of green coffee only the caffeine molecule migrates to the GCE; the other water-soluble coffee elements are retained in the green coffee.
Once the GCE is rich with caffeine it is then percolated through carbon absorbers which attract the caffeine molecule from the GCE while leaving other green coffee elements intact in the GCE. When the GCE is once again lean of caffeine it is then used to remove additional caffeine from the green coffee. This is a continuous batch process that takes 8–10 hours to meet the final residual decaffeinated target.