How does Decaf coffee work? Like isn’t caffeine naturally in the Coffea plant?
In: Biology
Indeed. Caffeine and related chemicals are found in all parts of the coffee plant. They are particularly concentrated in the seeds however the outer fruit containing the seeds also contains some caffeine.
Ripe coffee berries can be pressed for fresh juice which I have heard is pretty good and gives a bit of a kick like tea or coffee. This is a byproduct of some processes used to refine and seperate the seeds.
There are several methods to used to remove caffeine from coffee.
The simplest is to coarsely crush green coffee beans and rinse them in cold water at a few degrees C, then press the grounds to remove the cold solution, then repeating this a few times.
This takes advantage of the fact that caffeine is more soluble in cold water than most of the flavor compounds in coffee. This removes most of the caffeine but leaves most of the flavor. You can then dry and finish roast the coffee.
Another common method is the “Indirect solvent Process.” The green beans are brewed in hot water which is then filtered out, producing essentially a strong coffee, though green coffee isn’t terribly good tasting.
The resulting brew is then chilled and mixed and stirred with a hydrocarbon solvent like dichomethane or xylene. Neither of these are soluble in water and thus float to the surface as an oil layer. Caffeine is a lot more soluble in DCM or other such solvents than water so most of the caffeine is removed fron the brew, which then can be pumped off as a seperate layer.
The brew is then heated which boils out traces of the solvent remaining in the brew which you don’t want introduced into the coffee beans. The hot water is then recycled to brew more green beans. Because the recycled water is still rich in coffee flavors but is only poor in caffeine and a few other compounds, so overall not much flavor is lost from the beans.
Usually the coffee beans go through 2-3 sucessive steeping steps after which about 97-99% of the caffeine is removed.
The discarded solvent which is rich in caffeine but also contains some of the flavors may undergo a third step to selectively remove caffeine from it in turn. After which it can be heated to boil it off in a closed container and remaining flavor compounds can be added back to the coffee.
The solvent vapor is piped into a condenser as a gas then chilled and condensed back into a liquid, so it too can be reused. You don’t want to simply vent that stuff to the atmosphere.
Again, the green beans, caffeine removed, are dried then roasted before being packaged for sale.
Another method uses CO2 at high pressure. When pressurized, CO2 becomes a liquid although at ambient pressure it can only exist as a solid or a gas. By tweaking the pressure and temperature you can control the solubility of caffeine in the liquid CO2. The liquid CO2 is passed through the green coffee then scrubbed with water to remove the caffeine. Once the pressure is reduced the CO2 bubbles out of the water.
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