Caffeine is the naturally occurring substance in coffee that acts as a stimulant. Decaffeinated coffee has the caffeine removed through extra processing of the green beans and attempts to preserve as much of the original flavour as possible. Decaffeinated coffee needs to be at least 97% caffeine-free to be labelled decaffeinated.

There are four main methods for decaffeination.

Direct Chemical

The beans are steamed for about 30 minutes to open up the pores of the bean. They are then rinsed with a solvent chemical, either methylene chloride or ethyl acetate, for 10 hours to dissolve the caffeine. The caffeine saturated chemical is then drained away and the beans are steamed again to get rid of any solvent left over.

Ethyl acetate naturally occurs in ripening fruit. When this chemical is used, it is known as natural decaffeination.

Indirect Chemical

The beans are soaked in almost boiling water for several hours which extracts the caffeine and other flavour elements and oils from the beans. The beans are then removed and either dichloromethane or ethyl acetate is used to extract the caffeine from the water. The chemical bonds with the caffeine and when the mixture is heated the chemical and caffeine evaporate. The beans are then reintroduced to the liquid to reabsorb all of the flavours and oils.

This method is popular in Europe and is known as the European method.

Carbon dioxide (CO2)

Carbon dioxide decaffeination is a more recently introduced method. The beans are placed in a stainless steel tank which is then sealed and liquid CO2 is pumped in at high pressure. The CO2 dissolves the caffeine and leaves the larger flavour molecules behind. The carbon dioxide is then extracted to another tank where the pressure is released and it becomes a gas leaving behind caffeine particles. The gas is then pumped back into the tank under pressure and the process begins again.

This method is very costly and is used for large commercial quantities.

Swiss Water

The beans are soaked in hot water to dissolve the caffeine. The water is then removed and passed through a charcoal filter to remove the caffeine. The flavourless beans are then discarded and the water with all the flavour and oils is kept and called Green Coffee Extract (GCE).

The next batch of coffee beans is soaked in hot GCE. Because the GCE is saturated with coffee flavours and oils, only the caffeine passes into the GCE. The GCE is then filtered again and the caffeine removed and the process repeated for the next batch of beans.

This method is labelled as the Swiss Water technique and is popular with organic beans since no chemicals are used and 99% of the caffeine is removed.