Liquid CO2 decaffeination
In 1989, the Hermsen Company in Germany obtained a patent describing a decaffeination process with liquid CO2. The moisture content of the green beans has to be 45% to 55% and the CO2 has to be saturated with water, then decaffeination can be realised at very low temperatures (20-25°C) and at pressures between 65 and 70 bar. The separation of caffeine takes place by decompression below 60 bar in a separator; the caffeine-water mixture is reported to be very clean. The extraction time is about 60 hours, but due to the extremely low temperature the quality of the decaffeinated beans is said to be close to that of non-treated coffee. Practically all sugar inversions, Maillard and thermal decomposition reactions are avoided, particularly if careful low temperature moisturization and drying conditions complete the scheme.
The decaffeination of roasted ground coffee with liquid CO2 has been published in a patent from HAG. Moistened roast coffee is put in a pressure vessel which is connected in a cycle with another pressure vessel filled with a strong acid ion exchanger. To minimize the extraction of coffee aroma components, the temperature of the circulation CO2 is kept between 15 and 30°C and the pressure between 50 and 80 bar. After 2 to 3 hours the decaffeination is completed; the caffeine is almost selectively absorbed in the ion exchanger. Cleaning of the ion exchanger and recovery of the caffeine can be achieved by a desorption step with supercritical CO2. Remaining roast coffee components in the CO2 steam can be separated at the end by CO2 evaporation and aroma adsorption on the roasted coffee. The perceived quality of the coffee decaffeinated in such a manner is said to be equivalent to non-treated coffee in terms of flavour and aroma.