Wednesday, November 12, 2003

or this...

Chemical solvent decaffeination:

Firstly, the green beans are treated with steam, under pressure. This treatment swells the beans, increasing their surface area and making the caffeine easier to remove. The next stage is extraction of the caffeine by a solvent, again under pressure, at a temperature close to the boiling point of the solvent. Ideally, the solvent should remove caffeine selectively, without affecting the coffee in any other way. After decaffeination, only minute traces of the solvent are left in the coffee. Nevertheless, the chemical used must be sage, so that these traces do not affect the health of anyone drinking decaffeinated coffee. The safety of solvents used in decaffeination is tested in animal and human studies and reviewed by government scientific authorities. Solvents in current use which pass these stringent criteria include methylene chloride (dichloromethane) and ethyl acetate.

The caffeine which is removed from the solvent by distillation has many commercial applications, for example in pharmaceuticals and as a flavouring agent. Traces of solvent still adhering to the beans are forced out by further steaming and the coffee is then dried.

Decaffeination by supercritical gas:

At temperatures above their 'critical point' under pressure, gases behave rather like liquids and can be used as solvents. Supercritical carbon dioxide is used as a selective solvent for caffeine. It is applied to previously steamed green coffee at temperatures of about 70 degrees C and at high pressure. The caffeine is separated from the gas by rinsing or by absorption and the gas recirculated. In this method the wax layer of the coffee bean is retained and nothing but the caffeine is removed


Post a Comment

<< Home