What is supercritical CO2 decaffeination?

Supercritical CO2 decaffeination is the most precise and aroma-preserving method currently available. It uses carbon dioxide under high pressure and temperature to place it in a 'supercritical' state — neither fully liquid nor fully gaseous — which possesses the remarkable property of selectively dissolving caffeine while leaving the vast majority of the bean's aromatic compounds intact.

To understand supercritical CO2 decaffeination, one must first understand what a supercritical fluid is. When a substance is brought beyond its critical point in temperature and pressure, it enters a supercritical state where it simultaneously possesses the properties of a liquid (high density, dissolving capacity) and a gas (mobility, easy penetration into solid matrices). For CO2, this critical point is reached at 31.1°C and 73.8 bar pressure.

In the decaffeination process, green coffee beans are placed in a sealed chamber under supercritical CO2. The CO2 circulates through the beans and preferentially dissolves caffeine — a polar molecule with a particular affinity for supercritical CO2. Aromatic compounds (essential oils, organic acids, sugar precursors) are left intact because their solubility in supercritical CO2 is much lower than that of caffeine.

After extraction, the caffeine-laden CO2 is depressurised: caffeine precipitates and is recovered (then resold to the pharmaceutical and energy drink industries), and the CO2 is recycled in a closed loop. It is an ecologically clean method, with no solvent residues.

Why is this the most aroma-preserving method? Because it operates at a relatively low temperature (around 40-70°C) and without water or organic solvents. Classical chemical methods (using solvents such as methylene chloride or ethyl acetate) also dissolve aromatic compounds alongside caffeine. Swiss Water and Mountain Water avoid solvents but use water, which inevitably leaches certain soluble compounds.

The main drawback of supercritical CO2 is its very high investment cost (industrial installations cost tens of millions of euros), which limits it to specialist plants. But for decaf enthusiasts who do not want to sacrifice aromatic complexity, it is the method of choice.

Comparison of decaffeination methods