There is another method, Stemman says, which involves the use of “super critical carbon dioxide”. Beans that have been soaked in water are put in a stainless-steel extractor which is then sealed, and liquid CO2 blasted in at pressures of up to 1,000lbs per square inch. Like the Swiss Water method, it’s the C02 which binds with the caffeine molecules, drawing them out of the unroasted bean. The gas is then drawn off and the pressure is lowered, leaving the caffeine in a separate chamber.
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