Plate XIX · section 01 of 14

The problem comes down to one sentence of chemistry

THE PROCESS IN MOTION

Caffeine is held as a salt: it has to be freed before it can be extracted

Look at the pairs in the cell: as long as the line holds them together, the solvent passes through without taking anything. Water cuts the line, and the moisture gauge rises. Start the scene or choose a step.

The dry bean: caffeine held as a salt

In a green bean, caffeine does not move around freely. It is attached to chlorogenic acid in the form of a caffeine chlorogenate: a salt, that is, a pair of molecules held together by an electrical attraction. An organic solvent can carry off free caffeine; it cannot pull off caffeine held by a salt.

Read the stages without animation

The dry bean: caffeine held as a saltIn a green bean, caffeine does not move around freely. It is attached to chlorogenic acid in the form of a caffeine chlorogenate: a salt, that is, a pair of molecules held together by an electrical attraction. An organic solvent can carry off free caffeine; it cannot pull off caffeine held by a salt.
Swell: break the salt with waterWater, steam, sometimes acid: the bean goes from 10 to 12% moisture to 30 to 50%. The cell opens and the salt is hydrolyzed, that is, broken down by water. The caffeine becomes mobile.
Extract: carry off the caffeine that has become freeA solvent, charged water or CO₂ under pressure, in renewed baths until exhausted, carries off the caffeine that has become free, and only that if the process is selective. In the United States, at least 97% must be gone; in Europe, less than 0.1% must remain in the roasted bean. Neither text says zero.
Dry: make the bean storableSteam drives off the solvent, then drying brings the bean back to about 10 to 12%, without cooking it along the way. The second step is what sets the processes apart; it is the first and the third that damage the bean.

To remember: All the processes make the same three moves, in the same order: swell, extract, dry. Caffeine is not rinsed out; its salt is broken first.

In history: Ukers already reported it in 1922, based on Gorter's work.

Read the full article and its sources ↓

In a green bean, caffeine does not move around freely. It is attached to chlorogenic acid, the large family of acids in coffee, in the form of a caffeine chlorogenate: a salt, that is, a pair of molecules held together by an electrical attraction. This detail governs everything else. An organic solvent, a liquid able to dissolve fats and alkaloids, is perfectly able to carry off free caffeine; it cannot pull off caffeine held by a salt.

Ukers reported it as early as 1922, based on Gorter's work, and a century later every plant in the world still begins with the same maneuver: breaking this pair before trying to remove anything.

Ukers 1922, ch. XVIII (p. 174-188); professional training document, Caféine et procédés de décaféination, p. 2

Hence a constraint that the first manufacturers took twenty years to understand. Caffeine can be extracted from the roasted bean: it is far less tightly bound there, and the bean, riddled with pores by roasting, lets everything through. But the aromas go with it, and an aroma that has left does not come back. The green bean can be ground before extraction: the solvent reaches everything, but a green powder does not roast uniformly, and the result is a coffee burned on one side and raw on the other.

That leaves the only practicable route, and the most thankless: the whole green bean, whose tight structure resists precisely what one wants to do to it.

All the processes, from the benzene of 1905 to today's supercritical CO₂, therefore come down to the same three steps, in the same order:

Step	What is done	Why
Swell	Water, steam, sometimes acid, up to 30 to 50% moisture against 10 to 12% at the start	Open the cell and hydrolyze the salt, that is, break it down with water, to make the caffeine mobile
Extract	A solvent, or charged water, or CO₂ under pressure, in renewed baths until exhausted	Carry off the caffeine that has become free, and only that if the process is selective
Dry	Steam to drive off the solvent, then drying until the bean returns to about 10 to 12%	Make the bean storable and roastable, without cooking it along the way

It is the second step that sets the processes apart, and it is on this one that the commercial quarrels are played out. But it is the first and the third that damage the bean, and nobody makes a selling point of it. A bean that has been swollen to 40% water and then re-dried is no longer quite the bean it started as, whatever solvent is used in between. We come back to this further down, with figures.

One last constraint, a regulatory one this time, sets the target. In the United States, it is said everywhere that the Food and Drug Administration requires at least 97% of the caffeine to be gone; the text that would set this has not been found. In Europe, the rule concerns what remains and not what has been removed: in France, at most 0.1% caffeine in decaffeinated roasted beans, relative to the dry product, according to decree no. 91-340 of April 3, 1991; throughout the Union, at most 0.3% of the dry matter in an instant coffee extract, according to directive 1999/4/EC. Neither text says “zero,” and neither could: something always remains.

FDA, 97% rule not verified (part 163 of title 21 of the federal code, cited here previously, concerns cocoa); decree no. 91-340 of April 3, 1991, annex; directive 1999/4/EC; Wikipedia, Decaffeination, accessed on 09/18/2026

Coffee regulationCoffee regulation · section 02Names and composition: what may be called coffeeThe word “coffee” is reserved, and the rule that reserves it is French, dating from 1991 and still in force.

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