The Swiss Water process removes caffeine using only water, temperature and activated carbon filters.
How it works
Green coffee is soaked in water, which dissolves caffeine and the flavour compounds. That water is passed through carbon filters sized to trap caffeine molecules while letting flavour compounds through.
The result is green coffee extract saturated with flavour but free of caffeine. New batches of coffee are then soaked in that extract — so caffeine leaves the bean by diffusion, while flavour compounds have nowhere to go because the surrounding liquid is already saturated with them.
Why it matters
It removes around 99.9 per cent of the caffeine while retaining far more flavour than early solvent methods, and it uses no chemical solvents at all.
That makes it compatible with organic certification and the default for specialty decaf.
The alternatives
Mountain Water works on the same principle. CO2 processes use pressurised carbon dioxide. Solvent methods (ethyl acetate, methylene chloride) remain common commercially and are less gentle.
Brewing it
Grind a step coarser — decaffeinated beans are more brittle and extract faster.