Water decaffeination of coffee beans

Since water is required for pretreating green coffee beans and is a completely innocuous naturally occurring substance, it would at first sight appear to be an ideal solvent to use. in the extraction stage of a decaffeination process for coffee. Unfortunately coffee beans contain many other water-soluble substances (comprising about 20 weight % of the bean) in addition to caffeine and these should be retained as far as possible in the final decaffeinated product. 

In water decaffeination processes the beans (after the preliminary swelling operation) are washed and the aqueous extract is decaffeinated and then either fed back to the beans or reused for decaffeination. By using this decaffeinated solution as extractant a balance is established between the water-soluble substances (apart from caffeine) in the beans and in the extractant solution the extraction of these components is thus inhibited. The decaffeination of the aqueous solution is effected either by washing with suitable organic solvents or by adsorption. 

The adsorption method has in the past suffered from the non-availability of a truly selective adsorbent for caffeine. This difficulty is overcome in a 

Water decaffeination processes in which the aqueous extract is decaffeinated by contacting with an immiscible solvent such as methylene chloride have been in use for some years [12] and are described in the patent literature [16, 17]. 

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