Water Extraction

As in organic extraction, both the flavour ingredients and the caffeine are extracted in boiling water.  The solution is passed over charcoal and the caffeine is absorbed on to the surface.  Resoaking the beans in the caffeine-free solution can restore the original flavour.

In the “Swiss Water Process”, the beans are placed in caffeine-free “flavour charged water” and only caffeine is extracted from the beans, when passed over charcoal. 

This method is organic solvent free and the flavour is changed by only a small amount. 

Activated carbon filters are extremely porous and have an high surface area.  Raw carbon (e.g. coconut shells) is heated followed by activation, which occurs as oxidising gases are reacted on the surface of the carbon.

Physical adsorption to the pore walls is vital in AC filtration.  The best filtration processes occur when the pore size is only just large enough to accept a caffeine molecule.  Large molecules, which include most organic molecules, are most easily adsorbed.  The size of the pore can be altered to absorb only the caffeine molecule from the solution. 

A chemical interaction also occurs between carbon and the organic molecule.  The chemical properties in the pore can be altered to make a species have a greater cohesion with the carbon.  Organic molecules are similar in structure to the AC and a strong interaction occurs.   The caffeine is attracted to the carbon rather than remaining in the water solution.  The removal of caffeine therefore takes place. 

Organic molecules are adsorbed better at a lower temperature and pH and when the adsorption process occurs over a longer period, the amount of caffeine removed increases.