[jinz]

Hello I am a first year student in chemical engineering at the danish university; Aalborg Universitet.

I am writing a project about decaffeination of green coffee beans, and have encountered a problem that i cannot resolve.

In solvent decaffeination I know two of the most used solvents are methylene chloride (CH2Cl2) and ethyl acetate. In most of the litterature I have read it states that these solvents will extract caffeine selectively. My problem is why/how it will selectively extract caffeine, without affecting flavoring chemicals in the green coffee beans.

So far I realize that the caffeine molecule has both polar and nonpolar properties, and that the polarity of methylene chloride is limited. I assume this is what makes caffeine more soluble in the solvent, but I find it hard to believe that flavoring chemicals wont be extracted as well.

Any help will be greatly appreciated
Best Regards, Jens

[Arkcon]

You can begin to solve this problem for yourself by trying to understand some of the major flavor components, their structures, and compare them the structure of caffeine.  Briefly, caffeine is an alkaloid -- it has distinct chemical properties caused by its nitrogen containing groups.

I hate to send you an impossible task however, so I have to warn you, you should re-review the literature.  Decaffeination of green coffee beans by solvents definitely depletes them of other flavor compounds.  The industry extracts green coffee beans, removes the caffeine from the solvent, then re-uses the flavor-enhanced, caffeine depleted solvent, to remove caffeine from the next batch.

[jinz]

Thank you for the quick reply 
I know some industrial processes use flavor-charged water to extract only caffeine from the coffee beans, and then uses a solvent to extract the caffeine from the caffeine containing flavor-charged water. I have also read about a direct solvent proces in which the coffee beans are first steamed, and then rinsed in solvent.

As I understand it, some of the most important aromatic compounds in coffee include Guaiacol and Vanillin. When i review their composition, they are similar to caffeine in  terms of polarity.
I suppose that would mean that a solvent that will extract caffeine, will likely extract similar compounds as well? In that case I suppose quite a lot of flavor compounds will be extracted along with caffeine.

Best Regards, Jens