How is coffee decaffeinated

We continue our theme of coffee . Most coffees contain a large amount of the heterocyclic stimulant caffeine (I). Some people prefer to decrease the amounts of caffeine they ingest for health reasons, or they simply do not like to consume it at all, and they ask for decaffeinated coffee instead. 

The modem method of removing I from coffee resembles the operation of a coffee percolator, in which the water-soluble chemicals giving flavour, colour and aroma are leached from the ground-up coffee during constant irrigation with a stream of boiling water. 

Water is a good choice of solvent in a standard kitchen percolator because it removes all the water-soluble components from the coffee - hence the flavour. Clearly, however, a different solvent is required if only the caffeine is to be removed. Such a solvent must be cheap, have a low boiling point to prevent charring of the coffee and, most importantly, should leave no toxic residues. The presence of any residue would be unsatisfactory to a customer, since it would almost certainly leave a taste and there are also health and safety implications when residues persist. 

C02 is supercritical at temperatures and pressures above the critical point. 

Secondly, solid CO2 is relatively cheap. Finally, after caffeine removal, any occluded CO2 will vaporize from the coffee without the need to heat it or employ expensive vacuum technology. Again, we retain the volatile essential oils of the coffee. Even if some CO2 were to persist within the coffee granules, it is chemically inert, has no taste and would be released rapidly as soon as boiling water was added to the solid, decaffeinated coffee. 

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